# Fileset

[Materials Science in Semiconductor Processing-Manuscript -20230901-.pdf](https://mdr.nims.go.jp/filesets/d00db24e-f563-4262-a8f9-05bef49d77b6/download)

## Creator

Zilong Zhang, Keyun Gu, Tianyu Zou, Jian Huang, Ke Tang, Yue Shen, Haitao Ye, [Meiyong Liao](https://orcid.org/0000-0003-1361-4266), Linjun Wang

## Rights

[Creative Commons BY-NC-ND Attribution-NonCommercial-NoDerivs 4.0 International](https://creativecommons.org/licenses/by-nc-nd/4.0/)

## Other metadata

[Regulation of Te oxide layer on a CdZnTe film for adjusting surface contact of a CdZnTe-based device](https://mdr.nims.go.jp/datasets/90717eb9-7351-401c-8ac1-444f145e331e)

## Fulltext

1  Regulation of Te oxide layer on a CdZnTe film for adjusting 1 surface contact of a CdZnTe-based device 2  3 Zilong Zhang1, 2, *, Keyun Gu1, Tianyu Zou1, Jian Huang1, 3 *, Ke Tang1, Yue Shen1, 4 Haitao Ye4, Meiyong Liao2, and Linjun Wang1, 3 5  6 1 School of Materials Science and Engineering, Shanghai University, Shanghai 200444, 7 PR China. 8 2 Research Center for Functional Materials, National Institute for Materials Science 9 (NIMS), Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan. 10 3 Zhejiang Institute of Advanced Materials, SHU, Jiashan 314113, PR China. 11 4 School of Engineering, The University of Leicester, Leicester, LE1 7RH, United 12 Kingdom 13  14 Corresponding authors: Zilong Zhang (ZHANG.Zilong@nims.go.jp or 15 zlzhang16@hotmail.com) and Jian Huang (jianhuang@shu.edu.cn)  16  17 Abstract 18     The control of the interface states between the electric contacts and semiconductor 19 is a key issue to develop high-performance functional devices. The polishing, 20 passivation, and oxidation processes can optimize the surface states of the CdZnTe 21 (CZT) film to improve the contact characteristics with the electrode and tailor the 22 resistivity to control the electrical performance. In this work, a serial of surface 23 treatments including mechanical polishing (MP) + chemical polishing (CP) + surface 24 passivation (SP) were conducted to improve the surface states of the CZT film. A 25 transparent Ga-doped Zinc oxide (GZO) was used as the electrode to fabricate the 26 metal-semiconductor-metal (MSM) CZT-based device. The surface treatments of MP, 27 CP, and SP greatly improved the surface contact between CZT films and GZO 28 electrodes. By controlling the thickness of Te oxide layers on CZT film surfaces through 29 mailto:meiyong.liao@nims.go.jpmailto:zlzhang16@hotmail.commailto:jianhuang@shu.edu.cn2  the atmospheric oxidation (AO) and the no-atmospheric oxidation (NAO), the 30 thicknesses of oxide layers on CZT film surfaces were adjusted. The X-ray 31 photoelectron spectroscopy (XPS) was used to observe the oxidation sate of the Te 32 oxide layer. The thickness of the Te oxide layer of CZT film surface in atmosphere 33 environment was evaluated as 18~20 nm through the in-situ XPS measurement, while 34 that of the CZT film in insolated atmosphere was 5~7 nm. In contrast, the CZT film-35 based device under the combination treatments of MP + CP + SP + AO exhibit a surface 36 roughness of ~4 nm, leading to a significant reduction in the leakage current. The 37 present work provides a strategy to control the thickness of Te oxide layer of the CZT 38 film surface and fabricate a device with a lower current. 39  40 Keywords：CdZnTe film; GaZnO film; Surface contact; Oxide layer; XPS technique 41  42  43  44  45  46  47  48  49  50  51 3  1. Introduction 52 Cadmium zinc telluride (CdZnTe, CZT) has a wide and adjustable band gap (1.45-53 2.26), high average atomic number, high resistivity and facile fabrication process, 54 which make it as a promising material in the applications of particle radiation detectors, 55 health caring diagnosis and photodetectors [1-3]. Ultraviolet (UV) photodetectors have 56 garnered significant interest due to their widespread applications in industrial, 57 environmental, and biological fields [4-10]. Particularly, the CZT-based detectors have 58 recently attracted increasing attention for UV photodetection due to its high quantum 59 efficiency, high chemical stability, high mobility-lifetime product and simple growth 60 process [2, 3, 11-13]. Furthermore, the performance of a MSM CZT-based 61 photodetector depends not only on its film quality but also on the interface condition 62 between the film and the electrode [14-16]. In fact, the existence of high concentration 63 of interface states between the CZT film and the electrodes and the poor thermal 64 mismatch between the CZT film and the substrate hamper the development of CZT-65 based device with high performance [3, 12]. In order to circumvent the mismatch of 66 thermal dissipation between the as-deposited CZT film and substrate, a serial of 67 materials including fluorine-doped tin oxide (FTO) glass, indium-doped tin oxide (ITO) 68 glass, GaN, AlN, GaAs and Si were utilized as the substrates to grow CZT films [11, 69 17-20]. Furthermore, the surface treatments, including mechanical polishing (MP), 70 chemical polishing (CP) and surface passivation (SP) were developed to tailor the 71 surface morphology, roughness, and surface passivation layer. Zhang et al. used 72 4  MP+CP+SP treatments to obtain a CZT-based UV detector with a high photocurrent-73 to-dark current ratio of ~100 [3]. Tari et al. investigated that CP significantly altered the 74 surface morphology, roughness and structure of CZT [14]. Marchini et al. studied that 75 leakage currents can be reduced and contact stability improved by SP [21]. Park et al. 76 reported that SP could affect the metal-semiconductor contact, and in return, enhance 77 the peak-to-valley ratio of the energy spectrum [22]. Sang et al. proposed a novel two-78 step CP leads to a lower surface leakage current [23]. In order to achieve high electrical 79 performance through reducing the CZT surface roughness to enhance the adhesion with 80 electrodes and increasing the resistance to reduce the leakage current, the combination 81 of MP, CP, and SP treatments were usually adopted [3, 14, 24]. 82 Alternatively, the high-quality contact with little interface states and high barrier 83 height between the CZT film and the electrode is essential for CZT film-based detectors 84 with high performances. Through surface treatments, the interface state of the 85 electrode/CZT interface is greatly reduced. Furthermore, the barrier height of the 86 electrode/CZT is determined by the thickness of surface oxide layer of the CZT film. 87 Recently, a serial of researches pay more attention on the contact characteristics 88 including the enhancement of the geometric contact and the improvement of the contact 89 resistance between metal electrodes and CZT films [3, 11, 13, 25]. In addition, electrode 90 materials are usually opaque Au, Al, Pt, etc. However, the optical reflection in the metal 91 electrodes reduce the light exposure area and photo-response quantum efficiency. 92 Transparent conductive oxide (TCO) thin films are promising candidates for 93 5  photodetector to reduce the optical reflection by the electrodes. Ga-doped ZnO (GZO) 94 thin film, a transparent conductive film, hosts the merits of good conductivity, similar 95 thermal expansion coefficient, low cost, as well as facile fabrication process [26, 27]. 96 These merits afford GZO as a promising material to fabricate an electrode for CZT film-97 based devices [1, 28]. The oxidation behavior at interface between the GZO film and 98 the CZT film plays a critical role in determining the interface states of a CZT film-99 based device.  100 In this work, the CZT-based devices with the MSM structure were fabricated on 101 the glass substrates by the close-spaced sublimation (CSS) system and the magnetron 102 sputtering technique to investigate the oxidation of CZT film with and without the 103 atmospheric oxidation (AO). The XPS technique was utilized to investigate the 104 oxidation behavior. The CZT film with the GZO electrodes in lateral view was designed 105 to examine the electrical performance. Furthermore, I-V characteristics of CZT film-106 based devices under various surface treatments were examined. As a result, the CZT 107 film exposed to atmosphere environment produces the oxide layer with a thickness of 108 18~20 nm, while that of the CZT film in isolated atmosphere environment is 5~7 nm. 109 The CZT-based device under the surface combination treatments involving MP + CP + 110 SP + AO exhibits a low dark current as low as 9.3×10-8 A @1 V due to its adaptive 111 thickness of oxide layer and less surface defects. The regulation of the thickness of 112 oxide layer between the CZT and the electrode by surface treatments provides a useful 113 approach to enhance the electrical performance of the CZT-based devices. 114 6  2. Experimental 115 2.1 Films deposition and device fabrication 116 In this work, CZT films were deposited on 2 × 2 cm2 (L × W) fluorine-doped tin 117 oxide (FTO) glass substrates by CSS methods. The growth process for the CZT film 118 was discussed in detail in our pervious works [1, 29, 30]. Before the deposition of the 119 CZT films, the FTO glass substrates were sequentially cleaned in acetone, ethanol, and 120 deionized water for 5 min each. Then, they were dried by using a N2-gun in a clean-121 room. The CZT films were grown on the FTO glass substrates with a working pressure 122 of 4 Pa, a substrate temperature of 400℃, a target source temperature of 600℃, and a 123 growth duration of 3 h. The composition of the CZT target was Cd0.9Zn0.1Te, purchased 124 from Hefei Kejing Materials Technology Co.,Ltd, China. After the deposition of CZT 125 film, the CZT/glass sample was exposed in atmospheric condition for 12 h to produce 126 the natural oxidation. This sample was utilized to examine the oxidation behavior of 127 CZT film with AO treatment. Furthermore, another CZT/glass sample was kept in the 128 vacuum chamber to avoid the atmospheric oxidation. Then, GZO films were grown on 129 CZT/glass substrates through the RF magnetron sputtering system (MSP-300B). The 130 composition of the GZO ceramic target is Ga2O3: ZnO=2: 98 (wt%). The basic pressure 131 before the growth process was lower than 10-4 Pa. The growth parameters are: a 132 working pressure of 0.9 Pa, a sputtering power of 50 W, a substrate temperature of 300℃ 133 and a growth duration of 70 min. The formation of the GZO/CZT interface was 134 proposed to observe the oxidation of the CZT film without the atmosphere oxidation. 135 7  Alternatively, the mechanical polishing (MP) was carried out on the as-deposited CZT 136 films by using 50 nm-size Al2O3 particles for 3 h. The polishing particles were 137 uniformly dispersed in a polishing cloth with fluff. The same process of MP treatment 138 for the CZT film was utilized in our previous work [3, 30]. Then, the as-MP treated 139 CZT film was subjected to the chemical polishing (CP) under 2 vol% Br-MeOH 140 solution with the etching duration of 1 min. Furthermore, a surface passivation (SP) 141 layer was produced by the passivating treatment in NH4F (10 wt%) + H2O2 (10 wt%) 142 for 10 min. The GZO electrodes were produced on the as-surface treated CZT films 143 with and without the AO treatment via the magnetron sputtering technique. The various 144 kinds of samples treated by different surface treatments are shown in Table 1. The 145 GZO/CZT/GZO structure in the lateral view was utilized to examine the electrical 146 performance. The GZO electrode structure is characterized as an interdigitated finger 147 width of 0.5 mm, length of 10 mm and an interval of 1 mm. The thicknesses of the GZO 148 electrode and the CZT film are 180 nm and 220 nm. 149 Table 1 Various samples treated by different surface treatments 150 Samples Surface treatments T1 Mechanical polishing (MP)+ Atmospheric oxidation (AO) T2 MP+ Chemical polishing (CP)+AO T3 MP+ Surface passivation (SP)+AO T4 MP+CP+SP+AO T5 MP+ non-atmospheric oxidation (NAO) 8  T6 MP + CP + NAO  151 2.2 Characterization 152 The surface morphologies of the CZT films with various surface treatments were 153 examined by atomic force microscope (AFM) and scanning electron microscope (SEM, 154 JSM-7500F). The phase structures of the CZT films were analyzed via X-ray diffraction 155 (XRD) system by using Cu Ka radiation (λ = 1.54 Å). The composition and film quality 156 of CZT films were measured by Raman spectrometer (Horiba Jobin Yvons, HR800UV) 157 system, which is excited by 514.5 nm Ar+ wavelength laser with a spot diameter of 2 158 μm and a power of 1 W. X-ray photoelectron spectroscopy (XPS) analysis was 159 performed by using Thermo ESCALAB 250Xi X-ray photoelectron spectroscopy 160 equipped with Al Kα radiation (hν = 1486.6 eV) at a power of 150 W and a beam spot 161 diameter of 500 μm. The electrical properties of these detectors were measured by using 162 a Keithley 4200A-SCS (Semiconductor Characterization System) Parameter Analyzer.  163 3. Results and discussion 164 3.1 Microstructures of CZT films under various surface treatments 165 The AFM profiles of surface morphologies and roughness of CZT films under 166 different surface treatments are shown in Fig. 1(a-d). The CZT films are named as 167 T1~T4, as shown in Table 1. Some scratches appear on T1 surface as shown in Fig. 1(a) 168 due to the MP treatment. It can be seen that the preferential etching is occurred for T2 169 sample with a relative high roughness value compared to that of T1 sample, as depicted 170 9  in Fig. 1(b). The appearance of the increasing in surface roughness is effectively 171 eliminated by a layer produced from the SP treatment. For the T3 sample, although it is 172 subjected to the SP treatment, the surface morphology is similar to that of T1 sample, 173 as shown in Fig. 1(c). The surface scratches of T4 sample are basically removed, 174 resulting in the good surface condition with a small roughness value, as shown in Fig. 175 1(d). Fig. 1(e) shows the XRD patterns of the CZT films with different surface 176 treatments, demonstrating the main (111)-orientation of these CZT films. T4 sample 177 exhibits good surface quality due to the higher diffraction intensity. The crystal 178 structure parameters of various samples are listed in Table S1 (Supplementary material). 179 The 2θ of (111)-orientation shift with the various surface treatment. It is disclosed that 180 this shift shows weak dependence on the surface treatments. It can be seen that the full 181 width at half maximum (FWHM) of the CZT film under CP treatment is larger than that 182 of CZT film under merely MP treatment. The SP treatment is beneficial for reducing 183 FWHM after the CP treatment. The Raman spectra of CZT films are show in Fig. 1(f). 184 The peak at 123 cm-1 corresponds to Te element-related A1 mode, and the peak at 140 185 cm-1 corresponds to CZT-related TO1 (The transverse phonon oscillates) and Te 186 element-related E1 mode [29, 31-33]. The peaks at around 100 cm-1 and after 200 cm-1 187 represent the ETO (Te) mode and the LO2 (ZnTe) mode, respectively. No peaks of CdTe 188 and ZnTe and other impurities are observed, indicating the good quality for as-grown 189 CZT film. As we know, the peak intensity of Raman spectrum can be utilized to indicate 190 the content of vibrating groups of materials [34, 35]. It can be seen that the peak 191 10  intensities of T3 and T4 samples are significantly higher than that of T1 and T2 samples, 192 which demonstrates that these dense oxide films with high activity and content of 193 vibrating groups are formed on CZT film surfaces through the SP treatment. 194 Furthermore, T1 and T2 samples appear the peak at 166 cm-1 with weak intensity, 195 corresponding to the CZT-related LO1 (the longitudinal phonon oscillates) [31, 33]. 196  197 Fig. 1. (a-d) AFM images of CZT films after different surface treatments. T1 sample: 198 under mechanical polishing (MP) + atmospheric oxidation (AO). T2 sample: under MP 199 + chemical polishing (CP) + AO. T3 sample: MP + surface passivation (SP) + AO. T4 200 sample: under MP + CP + SP + AO. (e-f) XRD and Raman spectra of the CZT films 201 after different surface treatments. 202  203 3.2 Observation of oxidation behavior of CZT films through XPS tests 204 In this work, the XPS technique was applied for examining the existence and 205 thickness of surface oxide layer of the CZT film exposed to the atmosphere condition. 206 The fabrication of the GZO/CZT interface was also proposed to observe the oxidation 207 11  of the CZT film without the atmosphere oxidation. Before the XPS measurement, the 208 CZT film was subjected to the MP treatment. The SEM image of the cross-section of 209 GZO/CZT structure is shown in Fig. 2(a). It can be seen that the GZO film exhibits a 210 uniform and dense columnar morphology. An abrupt interface was observed in the 211 GZO/CZT contact interface. Fig. 2(b) depicts the schematic diagram of Ar ion etching 212 treatment of the GZO/CZT structure for the XPS measurement. The Ar ion is utilized 213 to etch the GZO film and the CZT film. The etching process was carried out on the 214 sample surface with an etching rate of 0.7 nm/s, which was checked by the standard 215 sample of tantalum pentoxide. The etching process and obtaining spectrum were 216 performed alternately. The binding energies of the elements involved in the XPS 217 measurement are listed in Table S2, which was utilized to judge the chemical states of 218 the elements [36]. To some extent, the contents and valence states of different elements 219 from different depths can be utilized to distinguish the materials in the certain area of 220 the GZO/CZT structure. 221 Figure 2(c) shows the photoelectron spectra of Te elements at three etching 222 positions of as-MP CZT film, which is exposed in the atmosphere. Due to the different 223 chemical environments of Te atoms, two peaks of Te 3d5/2 and Te3d3/2 with binding 224 energies of 572.6 eV and 583.1 eV, respectively, are appeared for Te element in the form 225 of CZT. It can be seen that this peak intensity at 572.6 eV and 583.1 eV increases with 226 the etching depth increasing from 120 s to 180 s, which confirms that the content of Te 227 element in the form of CZT is increased. Alternatively, two peaks of Te 3d5/2 and Te 228 12  3d3/2 (oxidation state) with binding energies of 576.2 eV and 586.6 eV, respectively, 229 emerge in the XPS spectrum as the etching time of 120 s. According to Table S2, these 230 two above peaks with higher binding energies are from the Te oxide. Moreover, these 231 two oxide peaks basically disappear when the etching time reached 135 s and 180 s. 232 Therefore, a native Te oxide was confirmed to be formed in atmosphere condition. 233 Based on the etching rate, the thickness of the atmospheric oxide layer of the CZT film 234 is evaluated to be 18~20 nm with the etching durations of 120~130 s. 235 Furthermore, in order to explore the existence of the oxide layer on this CZT film 236 surface, the photoelectron spectra of O elements with the etching time of 120 s and 180 237 s were analyzed, respectively, as shown in Fig. 2(d). When the etching time is 120 s, 238 the O 1s spectrum shows two separated peaks, namely, O1s scanA and O1s scanB [37, 239 38]. It is indicated that there are two different electron states in the 1s orbital of O 240 element. The binding energies of O1s scanA and O1s scanB are fitted to be 529.8 eV 241 and 531.3 eV, respectively. From Table S2, scanA and scanB represent the 1s electron 242 peak of O element in the Te oxide and the electron peak from the OH-/H2O, respectively. 243 The fitted higher binding energy of the O1s spectrum is close to that of scanA, which 244 is mainly from the Te oxide. The binding energy of O1s peak at the longer etching time 245 of 180 s is 530.3 eV, indicating the binding energy of adsorbent containing oxygen, 246 which may be formed in the chamber. The peak intensity decreased with increasing the 247 binding energy, indicating the content of Te oxide is higher than that of the adsorbent 248 containing oxygen. It illustrates that the content of Te oxide in the CZT film decreases 249 13  with the etching depth increasing, which is consistent with the photoelectron spectrum 250 of Te element in Fig. 2(c). 251  252 Fig. 2. (a) SEM image of cross-section of the GZO film grown on the CZT film. Scale 253 bar: 80 nm. (b) Schematic diagram of in-stiu XPS test of as-MP CZT surface under the 254 Ar ion etching. Depth imaging XPS spectra of (c) Te photoelectron and (d) O 255 photoelectron of as-MP CZT film under various etching durations. 256  257 Based on the existence of the Te oxide on the CZT film surface with AO treatment 258 through the photoelectron spectra of Te and O elements, the depth distributions of full 259 elements with the etching duration were analyzed by the XPS system, as shown in Fig. 260 GlassCZTAr+ etching(b)(a)GZO565 570 575 580 585 590 595 600Te3d3/2 of TeO2      586.6 eVTe3d5/2 of TeO2      576.2 eVTe3d3/2 of CZT       583.1 eV180 s135 s  Intensity (arb. units)Binding Energy (eV)120 sTe3d5/2 of CZT      572.6 eV528 532 536531.3 eV530.3 eVIntensity (arb. units)Binding Energy (eV) O1s 120 s O1s scanA 120 s O1s scanB 120 s O1s 180 s529.8 eV(c) (d)CZT14  3(a). Furthermore, in order to examine the existence of oxide layer and its thickness of 261 the GZO/CZT contact interface, the composition and characteristics of each element at 262 the GZO/CZT interface were analyzed via the Ar ion etching. The etching rate for GZO 263 film can be calculated based on the etching rate of standard sample, which is utilized to 264 estimate the thickness of contact interface. Fig. 3(a) exhibits the schematic diagram of 265 XPS test of the GZO/CZT interface through Ar ion etching. The depth distributions of 266 full elements of the GZO/CZT interface were also analyzed by the XPS system, as 267 shown in Fig. 3(b). It can be observed that there are co-existences of Zn, Ga and O 268 elements as the etching duration lower than 360 s. During the etching duration of 360 s 269 to 400 s, the Cd element begins to appear and its relative proportion increases with the 270 etching duration. The relative proportion of Ga element maintains weak change. The 271 relative proportions of Zn and O elements decrease with the etching duration. 272 Furthermore, the relative proportion of Te element (oxidation state) first increases and 273 then decreases to zero with the etching duration increasing. During the etching 274 durations from 390 s to 400 s, the Te element (bulk state) begins to appear and its 275 relative proportion increases with the etching duration. The relative proportion 276 variations of elements amongst the etching duration from 360 s to 400 s indicates that 277 the etching thickness in this etching interval is the thickness of oxide layer, which is 278 estimated to be about 5~7 nm based on the etching rate. According to the variations of 279 elements, Fig. 3(c) schematically shows the distribution of substances on the GZO/CZT 280 interface. 281 15  In order to further analyze the reason of the existence of Te oxide at the GZO/CZT 282 interface, the XPS spectra of Te element at this interface are depicted in Fig. 3(d). It 283 shows that at the etching duration of 360 s, the electron peaks of Te elements (oxidation 284 state and bulk state) exhibit weak intensities, which illustrates this examined area is in 285 GZO film. With the etching duration increasing, the electron peaks of Te elements with 286 the oxidation state of 571.4 eV and the bulk state of 581.7 eV appear during the etching 287 durations of 375~400 s. As the etching duration larger than 400 s, the electron peak of 288 Te element (oxidation state) basically disappears, while the peak intensity of Te element 289 (bulk state) is significantly enhanced, which demonstrates this examined area is in the 290 CZT film. In overall, in view of the XPS spectra of Te elements, it can be obtained that 291 the existence of weak permeation diffusion and chemical reaction in GZO/CZT 292 interface, which is consistent with the result in Fig. 3(b).  293 16   294 Fig. 3. (a) Schematic diagram of XPS test of the GZO/CZT structure under the Ar ion 295 etching. (b) Dependences of atomic percentage of full elements in the GZO/CZT 296 interface on different etching durations. (c) Schematic diagram of element distribution 297 inthe GZO/CZT structure. (d) Depth profiling XPS spectra of Te element in the 298 GZO/CZT structure with different etching durations. 299  300 3.3 Electrical performance of GZO/CZT/GZO structure device  301 As discussed in 3.2 chapter, it can be obtained that the CZT film exposed to the 302 atmosphere environment produced the oxide layer with a thickness of 18~20 nm, while 303 that of the CZT film in the GZO/CZT structure is significantly limited due to the weak 304 EtchingCZT (bulk)TeO2, CZT (bulk), GaTeO2, GZO, CdGZO120 180 240 300 360 420 480 540010203040506070  Atomic percentage (%)Etching time (s) Zn2p Ga2p O1s O1s (contamination) Cd3d Te3d (oxide) Te3d (bulk)Te-OExtendedInterface(a) (b)560 565 570 575 580 585 590 595 600585.4 eV581.7 eV576.2eVTe 3d3/2 of TeO2Te 3d5/2 of TeO2Te 3d3/2 of CdZnTe450 s405 s390 s375 s  Intensity (arb. units)Binding Energy (eV)360 sTe 3d5/2 of CdZnTe571.4 eVGlassCZTGZOAr+ etching(c) (d)17  interaction at interface, showing the thickness is 5~7 nm. In the CZT-based device, the 305 thicknesses of the GZO electrode and the CZT film are 180 nm and 220 nm. In general, 306 the electrical performance of a GZO/CZT/GZO device is determined by the GZO/CZT 307 interface states. The interface states and barrier height between the CZT film and the 308 electrode show strong relationship with the thickness of oxide layer of CZT film. The 309 GZO film exhibits a bright promising to act as an electrode material for a CZT film-310 based device due to the controlled thickness of oxide film in the GZO/CZT structure. 311 The aim of these electrical measurements is to figure out the suitable surface treatments 312 to fabricate the UV CZT-based photodetector with a low dark current, which is in favor 313 of achieving high photodetection performance. In our previous work, the surface state 314 of the CZT film can be tailored through the surface treatments [3]. Here in this study, 315 the influence of the oxide layer on electrical performance of CZT film-devices after 316 various surface treatments was examined. Furthermore, after these surface treatments, 317 two CZT films were kept in the vacuum chamber to avoid the atmosphere, as called T5 318 sample (subjected to MP+ non-atmospheric oxidation (NAO)) and T6 sample 319 (subjected to MP + CP + NAO). Fig. 4(a) exhibits the schematic diagram of a CZT-320 based devices with the interdigital GZO electrodes. The photo image of a CZT-based 321 detector is shown in Fig. S1. In addition, Fig. 4(b) depicts the I-V plots of CZT film- 322 devices with different surface treatments, demonstrating that the dark-currents vary 323 with the applied voltage. The dark current is utilized to reflect the contact performance 324 for these devices after various surface treatments. The low dark current indicates the 325 18  good contact in the interface with low defects. For T1 sample, the device has a low dark 326 current. The I-V curve of T2 sample has good symmetry feature. The dark current is 327 obviously larger than that of T1 sample due to the enrichment of Te element on the CZT 328 surface after CP treatment [3]. T3 sample also has a large dark current. The T4 sample 329 possesses low dark current od ~9.3×10-8 A @1 V. Compared with the dark currents of 330 T3 sample and T4 sample, it can be obtained that the SP on the CZT film surface after 331 MP + CP treatments is more beneficial to reduce the surface states. This is due to that 332 the CP treatment can smooth the CZT film surface, remove surface damage, and form 333 the stable oxide layer. Furthermore, the I-V plot of T5 sample exhibits a high dark 334 current. It indicates the existence of weak interaction between the GZO electrode and 335 as-MP CZT film with the NAO treatment. The more capture energy levels caused by 336 interface defects lead to the dark current increasing. The dark current of T6 sample 337 sharply increases due to an obvious decrease in surface resistance. After MP + CP + 338 NAO treatments, the CZT film exhibits a very poor interface state, which results in the 339 serious deterioration of stoichiometry. Thus, the CZT film suffered from the NAO 340 treatment is not suitable for fabricating the CZT-device with a low dark current. 341 19   342 Fig. 4. (a) Schematic setup of a CZT-based UV device. (b) Dependences of dark current 343 on the applying voltage at dark conditions. 344  345 Based on the I-V plots of the CZT film-based detectors under various surface 346 treatments, it can be seen that the existence of the Te oxide layer and its thickness play 347 a critical influence on the electrical performance. The Te oxide layer is in favor of 348 limiting the dark current. For the T1 sample with MP + AO treatments, it can produce 349 the adequate oxide layer on film surface, which results in the highest barrier height and 350 the lowest dark current. The thickness of the oxide layer under the AO treatment is 351 evaluated as a value of 18~20 nm. The SP treatment can circumvent the issue of the Te 352 enrichment on the film surface due to the CP treatment (see IT3 < IT2). The T4 sample 353 with the combination of surface treatments involving MP + CP + SP + AO treatments 354 exhibits the low dark current due to its adaptive thickness of oxide layer and good 355 surface state. These T5 and T6 samples with the NAO treatment have limited thickness 356 of oxide layer and the low barrier height, which leads to the large dark current. The AO 357 treatment is beneficial for the CZT film to obtain the suitable thickness of oxide layer 358 -10 -5 0 5 1010-310-210-1100101102103104105Current (A)Voltage (V) T1  T4 T2  T5 T3  T6Keithley4200-SCS(a) (b)Glass CZT GZO20  and optimal barrier height. 359  360 4. Conclusion 361 In summary, CZT films were grown on FTO glass substrates by the CSS system. 362 The oxidation behaviors of these CZT films with and without the AO treatment were 363 observed through the XPS technique. The results show that the thickness of oxide layer 364 of the CZT film surface exposed to atmosphere environment is evaluated as 18~20 nm, 365 while that of the CZT film in the GZO/CZT structure with NAO treatment was 5~7 nm. 366 The surface treatments, including MP, CP and SP are utilized to reduce the surface 367 roughness and improve the surface condition to obtain a better adhesion and contact 368 between the GZO and the CZT. Furthermore, the large thickness of oxide insulating 369 layer is in favor of increasing the resistance and reducing dark current. The CZT-based 370 device with surface combination treatments of MP + CP + SP + AO exhibits a low dark 371 current of 9.3×10-8 A @1 V, which is essential for the fabrication of devices with high 372 signal-to-noise ratio. The regulation of oxide layer on the CZT film surface offers a 373 promising strategy for fabricating CZT-based devices with high electrical performance.  374  375 Declaration of Competing Interest 376 The authors declare that they have no known competing financial interests or 377 personal relationships that could have appeared to influence the work reported in this 378 paper. 379 21   380 Acknowledge 381 This work was funded by National Science Foundation of China (No. 11875186 382 and No. 11905121, No. 11775139). 383  384 References 385 [1] T. Zou, J. Huang, Y. Hu, K. Tang, Z. Zhang, X. Zhou, Y. Shen, J. Zhang, L. Wang, 386 Y. Lu, CdZnTe thick film radiation detectors with B and Ga co-doped ZnO contacts, 387 Surf. Coat. Technol., 360 (2019), 64-67. 388 [2] S.N. Moger, M. Mahesha, Investigation on ZnTe/CdxZn1-xTe heterostructure for 389 photodetector applications, Sens. Actuator A Phys., 315 (2020), 112294. 390 [3] Z. Zhang, K. Gu, F. Yang, J. Huang, K. Tang, Y. Shen, J. Zhang, M. Liao, L. Wang, 391 Enhanced UV detection performance of a CdZnTe-based photodetector through surface 392 polishing treatments, J. Mater. Chem. C, 9(10) (2021), 3601-3607. 393 [4] H. Yang, S. Cai, Y. Zhang, D. Wu, X. Fang, Enhanced electrical properties of 394 lithography-free fabricated MoS2 field effect transistors with chromium contacts, The 395 J. Phys. Chem. Lett., 12(11) (2021), 2705-2711. 396 [5] Z. Li, T. Yan, X. Fang, Low-dimensional wide-bandgap semiconductors for UV 397 photodetectors, Nat. Rev. Mater., (2023), 1-17. 398 [6] X. Xu, J. Chen, S. Cai, Z. Long, Y. Zhang, L. Su, S. He, C. Tang, P. Liu, H. Peng, 399 X. Fang, A real-time wearable UV-radiation monitor based on a high-performance p-400 CuZnS/n-TiO2 photodetector, Adv. Mater. 30(43) (2018), 1803165. 401 [7] Y. Chen, L. Su, M. Jiang, X. Fang, Switch type PANI/ZnO core-shell microwire 402 heterojunction for UV photodetection, J. Mater. Sci. Technol., 105 (2022) 259-265. 403 [8] M. Deng, Z. Li, X. Deng, Y. Hu, X. Fang, Wafer-scale heterogeneous integration of 404 self-powered lead-free metal halide UV photodetectors with ultrahigh stability and 405 homogeneity, J. Mater. Sci. Technol., 164 (2023), 150-159. 406 [9] M. Liao, Progress in semiconductor diamond photodetectors and MEMS sensors, 407 Functional Diamond 1(1) (2022), 29-46. 408 [10] M. Imura, M. Togawa, M. Miyahara, H. Okumura, J. Nishinaga, M. Liao, Y. Koide, 409 Highly tolerant diamond Schottky barrier photodiodes for deep-ultraviolet xenon 410 excimer lamp and protons detection, Functional Diamond 2(1) (2022), 167-174. 411 [11] Y. Shen, Y. Xu, J. Sun, Z. Zhang, J. Huang, M. Cao, F. Gu, L. Wang, Interface 412 regulation and photoelectric performance of CdZnTe/AlN composite structure for UV 413 photodetector, Surf. Coat. Technol. 358 (2019), 900-906. 414 [12] J. Sun, Y. Shen, R. Chen, J. Huang, M. Cao, F. Gu, L. Wang, J. Min, Effect of ZnTe 415 22  transition layer to the performance of CdZnTe/GaN multilayer films for solar-blind 416 photodetector applications, J. Phys. D: Appl. Phys. 53(41) (2020), 415105. 417 [13] M. Shkir, M.T. Khan, I. Ashraf, A. Almohammedi, E. Dieguez, S. AlFaify, High-418 performance visible light photodetectors based on inorganic CZT and InCZT single 419 crystals, Sci. Rep., 9(1) (2019), 1-9. 420 [14] S. Tari, F. Aqariden, Y. Chang, C. Grein, J. Li, N. Kioussis, Impact of surface 421 treatment on the structural and electronic properties of polished CdZnTe surfaces for 422 radiation detectors, J. Electron. Mater., 42(11) (2013), 3252-3258. 423 [15] S. Del Sordo, L. Abbene, E. Caroli, A.M. Mancini, A. Zappettini, P. Ubertini, 424 Progress in the development of CdTe and CdZnTe semiconductor radiation detectors 425 for astrophysical and medical applications, Sensors, 9(5) (2009), 3491-3526. 426 [16] A. Brovko, A. Adelberg, L. Chernyak, S. Gorfman, A. Ruzin, Impact of polishing 427 on crystallinity and static performance of Cd1-xZnxTe, Nucl. Instrum. Meth. A, 984 428 (2020), 164568. 429 [17] S. Chander, M. Dhaka, Optimization of structural, optical and electrical properties 430 of CdZnTe thin films with the application of thermal treatment, Mater. Lett., 182 (2016), 431 98-101. 432 [18] S. Chander, M. Dhaka, Enhanced structural, electrical and optical properties of 433 evaporated CdZnTe thin films deposited on different substrates, Mater. Lett., 186 434 (2017), 45-48. 435 [19] S. Chander, A. Purohit, S. Patel, M. Dhaka, Effect of substrates on structural, 436 optical, electrical and morphological properties of evaporated polycrystalline CdZnTe 437 thin films, Physica E Low Dimens. Syst. Nanostruct., 89 (2017), 29-32. 438 [20] J. Gao, W. Jie, Y. Yuan, T. Wang, Y. Xie, Y. Wang, Y. Huang, J. Tong, H. Yu, G. 439 Pan, One-step fast deposition of thick epitaxial CdZnTe film on (001) GaAs by close-440 spaced sublimation, CrystEngComm, 14(5) (2012), 1790-1794. 441 [21] L. Marchini, A. Zappettini, E. Gombia, R. Mosca, M. Lanata, M. Pavesi, Study of 442 surface treatment effects on the metal-CdZnTe interface, IEEE Trans. Nucl. Sci., 56(4) 443 (2009), 1823-1826. 444 [22] S. Park, J. Ha, Y. Cho, H. Kim, S. Kang, Y. Kim, J. Kim, Surface passivation effect 445 on CZT-metal contact, IEEE Trans. Nucl. Sci., 55(3) (2008), 1547-1550. 446 [23] S. Wenbin, W. Kunshu, M. Jiahua, T. Jianyong, Z. Qi, Q. Yongbiao, A novel two-447 step chemical passivation process for CdZnTe detectors, Semicond. Sci. Technol., 20(5) 448 (2005), 343. 449 [24] M. Duff, D. Hunter, A. Burger, M. Groza, V. Buliga, D.R. Black, Effect of surface 450 preparation technique on the radiation detector performance of CdZnTe, Appl. Surf. 451 Sci., 254(9) (2008), 2889-2892. 452 [25] R. Chen, Y. Shen, T. Li, J. Huang, F. Gu, X. Liang, M. Cao, L. Wang, J. Min, 453 Interface optimization of free-standing CdZnTe films for solar-blind ultraviolet 454 detection: Substrate dependence, Vacuum, 193 (2021), 110484. 455 [26] T. Nam, C.W. Lee, H.J. Kim, H. Kim, Growth characteristics and properties of Ga-456 doped ZnO (GZO) thin films grown by thermal and plasma-enhanced atomic layer 457 23  deposition, Appl. Surf. Sci., 295 (2014), 260-265. 458 [27] S.H. Chang, H.-M. Cheng, C.-L. Tien, S.-C. Lin, K.-P. Chuang, Optical, electrical 459 and mechanical properties of Ga-doped ZnO thin films under different sputtering 460 powers, Opt. Mater., 38 (2014), 87-91. 461 [28] Y. Shen, J. Huang, Q. Gu, H. Meng, K. Tang, Y. Shen, J. Zhang, L. Wang, Y. Lu, 462 The investigation of Ga-doped ZnO as an interlayer for ohmic contact to Cd1-xZnxTe 463 films, Appl. Surf. Sci., 425 (2017), 176-179. 464 [29] J. Huang, Q. Gu, F. Yang, K. Tang, S. Gou, Z. Zhang, Y. Shen, J. Zhang, L. Wang, 465 Y. Lu, Growth and properties of CdZnTe films on different substrates, Surf. Coat. 466 Technol., 364 (2019), 444-448. 467 [30] F. Yang, J. Huang, T. Zou, K. Tang, Z. Zhang, Y. Ma, S. Gou, Y. Shen, L. Wang, Y. 468 Lu, The influence of surface processing on properties of CdZnTe films prepared by 469 close-spaced sublimation, Surf. Coat. Technol., 357 (2019), 575-579. 470 [31] G.A. Kulkarni, V. Sathe, K. Rao, D. Muthu, R. Sharma, Micro-Raman imaging of 471 Te precipitates in CdZnTe (Zn∼ 4%) crystals, J. Appl. Phys., 105(6) (2009), 063512. 472 [32] H. Xu, R. Xu, J. Huang, J. Zhang, K. Tang, L. Wang, The dependence of Zn content 473 on thermal treatments for Cd1-xZnxTe thin films deposited by close-spaced 474 sublimation, Appl. Surf. Sci., 305 (2014), 477-480. 475 [33] J. Min, X. Liang, J. Chen, D. Wang, H. Li, J. Zhang, Investigation of Te inclusions 476 in CdZnTe crystalline material using Raman spectroscopy and IR techniques, Vacuum, 477 86(7) (2012), 1003-1006. 478 [34] A.K. Yadav, P. Singh, A review of the structures of oxide glasses by Raman 479 spectroscopy, RSC Adv., 5(83) (2015), 67583-67609. 480 [35] P. Colomban, A. Slodczyk, Raman intensity: An important tool to study the 481 structure and phase transitions of amorphous/crystalline materials, Opt. Mater., 31(12) 482 (2009), 1759-1763. 483 [36] J.F. Moulder, Handbook of X-ray photoelectron spectroscopy, Physical electronics  484 (1995) 230-232. 485 [37] C. Zhang, J. Sunarso, S. Liu, Designing CO2-resistant oxygen-selective mixed 486 ionic–electronic conducting membranes: guidelines, recent advances, and forward 487 directions, Chem. Soc. Rev., 46(10) (2017), 2941-3005. 488 [38] L. Wu, Y. Li, S. Li, Z. Li, G. Tang, W. Qi, L. Xue, X. Ge, L. Ding, Method for 489 estimating ionicities of oxides using O1s photoelectron spectra, AIP Adv., 5(9) (2015), 490 097210. 491  492