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[色川 芳宏](https://orcid.org/0000-0002-6531-4356), [大井 暁彦](https://orcid.org/0000-0003-4638-0099), [生田目 俊秀](https://orcid.org/0000-0002-5973-0230), [小出 康夫](https://orcid.org/0000-0001-8321-9822)

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[Pt/GaN Schottky barrier height lowering by incorporated hydrogen](https://mdr.nims.go.jp/datasets/68dbabce-5659-480d-a9d9-9b9d8472847b)

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Pt/GaN Schottky Barrier Height Lowering by Incorporated HydrogenECS Journal of Solid StateScience and Technology     OPEN ACCESSPt/GaN Schottky Barrier Height Lowering byIncorporated HydrogenTo cite this article: Yoshihiro Irokawa et al 2024 ECS J. Solid State Sci. Technol. 13 045002 View the article online for updates and enhancements.You may also likeAmbient-hydrogen-induced changes in thecharacteristics of Pt/GaN Schottky diodesfabricated on bulk GaN substratesYoshihiro Irokawa, Tomoko Ohki,Toshihide Nabatame et al.-Impact of graphene interlayer onperformance parameters of sandwichstructure Pt/GaN Schottky barrier diodesJ X Ran, B Y Liu, X L Ji et al.-Dilute Hydrogen Sulfide SensingCharacteristics of a Pt/GaN SchottkyDiodeJian-Feng Xiao, Chen-Pin Hsu and Yu-LinWang-This content was downloaded from IP address 144.213.253.16 on 09/04/2024 at 23:20https://doi.org/10.1149/2162-8777/ad3959https://iopscience.iop.org/article/10.35848/1347-4065/ac0260https://iopscience.iop.org/article/10.35848/1347-4065/ac0260https://iopscience.iop.org/article/10.35848/1347-4065/ac0260https://iopscience.iop.org/article/10.1088/1361-6463/ab9a9bhttps://iopscience.iop.org/article/10.1088/1361-6463/ab9a9bhttps://iopscience.iop.org/article/10.1088/1361-6463/ab9a9bhttps://iopscience.iop.org/article/10.1149/MA2015-01/22/1427https://iopscience.iop.org/article/10.1149/MA2015-01/22/1427https://iopscience.iop.org/article/10.1149/MA2015-01/22/1427https://pagead2.googlesyndication.com/pcs/click?xai=AKAOjssdXrEeUiRdzknhoDtFGVKFLPoEsTeALOXpP3BLN8mPDp7-UOcgZA6BZP1Y5b1wKsnMcMh_kZSS_xrMDMYsc-rzBeCnSExXQqvPEgHh8J5Z5moUy8pwZ2diJsB7M0VeXny5xg4Wx4Kw83Kb-l81MBo1NwQA2cg0TEB8RgalsY3o_kWu2JM6UJigFeBq-eYMDU2389Prh8WHxH4JE_yIaO5dcudwq8XwkUf13fRY5AImc8yJNDXmu-Y5hz4C9l2ZQ2NDEF17AdHD7pqPro1jcGcmwDtvDH0u6VvZbkG5VPiG_hfobkESiKlpabYQjYvC3kEM_A9D8vfliH5j3eC_bNQ&sig=Cg0ArKJSzGCcAInsJeli&fbs_aeid=%5Bgw_fbsaeid%5D&adurl=https://www.el-cell.com/products/pat-battery-tester/pat-tester-i-16/%3Fmtm_campaign%3Diop%2520pdf%2520advert%26mtm_kwd%3Dpat-tester-i-16%26mtm_source%3Dpdf%26mtm_cid%3D2024Pt/GaN Schottky Barrier Height Lowering by IncorporatedHydrogenYoshihiro Irokawa,z Akihiko Ohi, Toshihide Nabatame, and Yasuo KoideNational Institute for Materials Science, Tsukuba, Ibaraki 305-0044, JapanChanges in the hydrogen-induced Schottky barrier height (ΦB) of Pt/GaN rectifiers fabricated on free-standing GaN substrates wereinvestigated using current–voltage, capacitance–voltage, impedance spectroscopy, and current–time measurements. Ambienthydrogen lowered the ΦB and reduced the resistance of the semiconductor space–charge region while only weakly affecting theideality factor, carrier concentration, and capacitance of the semiconductor space–charge region. The changes in the ΦB werereversible; specifically, the decrease in ΦB upon hydrogen exposure occurred quickly, but the recovery was slow. The results alsoshowed that exposure to dry air and/or the application of a reverse bias to the Schottky electrodes accelerated the reversioncompared with the case without the applied bias. The former case resulted in fast reversion because of the catalytic effect of Pt. Thelatter case, by contrast, suggested that hydrogen was incorporated into the Pt/GaN interface oxides as positive mobile charges.Moreover, both exposure to dry air and the application of a reverse bias increased the ΦB of an as-loaded sample from 0.91 to1.07 eV, revealing that the ΦB of Pt/GaN rectifiers was kept lower as a result of hydrogen incorporation that likely occurred duringdevice processing and/or storage.© 2024 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open accessarticle distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2162-8777/ad3959]Manuscript received March 17, 2024. Published April 9, 2024.Gallium nitride (GaN) has been extensively used in optical andelectronic devices because of its advantages,1 which include a wide(3.4 eV) direct bandgap, easy fabrication of heterostructures usingnitride-based materials such as AlGaN and InGaN, and a highsaturation velocity (e.g., 1.9 × 107 cm s−1 at a sheet charge densityof 7.8 × 1011 cm−2 at room temperature).2 As the commercializationof high-quality free-standing bulk GaN substrates proceeds, re-searchers are dramatically improving the performance of GaNelectronic devices by exploiting the advantages of substrates witha low dislocation density; consequently, a wide variety of GaN-based devices, including Schottky barrier diodes (SBDs),3 p–njunction diodes,4 junction-barrier Schottky diodes,4,5 and metal-oxide-semiconductor field-effect transistors (MOSFETs),3,6,7 haverecently attracted much attention. Nonetheless, knowledge of thereliability of these devices remains limited and little is known aboutthe suitability of these devices for use in real electronic structuressuch as power conversion systems. Among factors affecting thedevice reliability, hydrogen incorporation into devices can causeserious complications in device characteristics because hydrogenubiquitously exists in semiconductor processing and in the storageenvironment and easily penetrates into the device materials, chan-ging the device characteristics unintentionally.8–11 In the case ofMOSFETs, the effects of ambient hydrogen on Si and SiC deviceshave long been studied; hydrogen-induced dipole layers have beenproposed to be the primary factor leading to changes in the thresholdvoltages of these devices.12 With respect to GaN metal-oxide-semiconductor (MOS) capacitors, by contrast, we recently reportedthat ambient hydrogen was incorporated into dielectric layers aspositively charged mobile ions, leading to flatband voltage shifts ofthe devices.13 In that report, we revealed that oxide layers in MOSdevices played a critical role in the flatband voltage shifts; that is, wespeculated that the flatband voltage shifts originated from trappedhydrogen at oxygen vacancies (VOs) in the oxide layers.13 Inaddition, even for GaN SBDs, we found that the formation ofoxides at the Pt/GaN interface might be responsible for the reductionof the Schottky barrier height (ΦB) as a result of hydrogenexposure.14,15 That is, we hypothesized that hydrogen trapped atVOs in the Pt/GaN interface oxide changed the resistivity of theoxide layers, resulting in the ΦB reductions.In our previous study involving GaN MOS capacitors, theapplication of a reverse gate bias during the reversion revealed thecharging state of hydrogen in the oxide layers.13 For GaN SBDs,however, the charging state of hydrogen is unknown. In the presentstudy, we used current–voltage (I–V), capacitance–voltage (C–V),impedance spectroscopy, and current–time (I–t) measurements toinvestigate the charging state, along with the hydrogen response andreversion characteristics, of Pt/GaN SBDs. As a result, we found thathydrogen can be incorporated into the native oxide at the Pt/GaNinterfaces as positive mobile charges, as previously observed in GaNMOS capacitors. In addition, we found that the ΦB of Pt/GaNrectifiers is kept lower because of the hydrogen incorporation at thePt/GaN interface oxides, which likely occurs during device proces-sing and/or storage, where the incorporated hydrogen does notdesorb under conventional conditions such as room temperature andhumid ambient air.ExperimentalFigure 1 shows a schematic cross-section of the Pt/GaN SBDstructure investigated in the present study. The devices wereprepared as follows: 5 μm-thick GaN layers were epitaxially grownon free-standing bulk n+-GaN(0001) substrates via metal-organicvapor-phase epitaxy. The grown GaN layers were doped with Si at aconcentration of 2 × 1016 cm−3, and the substrates had a dislocationdensity on the order of approximately 106 cm−2 and a carrierconcentration of 1 × 1018 cm−3. After the surface was cleanedwith a mixture of sulfuric acid and hydrogen peroxide (H2SO4:H2O2= 1:1) to remove organic residues, Ti (20 nm)/Al (100 nm)/Pt(40 nm)/Au (100 nm) back Ohmic contacts were patterned viaelectron-beam deposition. The patterned substrates were thenannealed at 750 °C for 30 s under a flowing N2 atmosphere in arapid thermal annealing system. After formation of the Ohmiccontacts, circular Pt (25 nm) Schottky contacts with a diameter of100 μm were formed through a lift-off process. Notably, weconfirmed that this surface cleaning method led to the generationof crystalline native gallium oxide layers with a thickness of ∼1 nmon their surfaces; the in-plane lattice constant of the oxide matchedthat of GaN.16,17The reaction of the fabricated devices to ambient hydrogen gaswas studied at room temperature in a stainless-steel chamber equippedwith tungsten probes. After the chamber was evacuated by a dry scrollvacuum pump, flowing pure N2 gas was introduced at a rate of100 mLmin−1 and a total pressure of 10.0 kPa; I–V, C–V, andimpedance spectroscopy measurements were then conducted underpure N2 gas. Next, in place of pure N2 gas, flowing 1% H2 + N2zE-mail: IROKAWA.Yoshihiro@nims.go.jpECS Journal of Solid State Science and Technology, 2024 13 045002https://orcid.org/0000-0002-6531-4356http://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/https://doi.org/10.1149/2162-8777/ad3959https://doi.org/10.1149/2162-8777/ad3959mailto:IROKAWA.Yoshihiro@nims.go.jphttps://crossmark.crossref.org/dialog/?doi=10.1149/2162-8777/ad3959&domain=pdf&date_stamp=2024-04-09mixture gas was introduced at the same flow rate and same totalpressure and the devices in pure N2 gas were measured using the samemethods after saturation of the device characteristics. For somedevices, the hydrogen reaction transient was also recorded using theI–t method. Finally, the flowing gas was changed from 1% H2 + N2mixture gas to either pure N2 gas or dry air gas at the same flow rateand same total pressure; the recovery transients for some of thedevices were then measured using the I–t technique. All the I–V andC–V measurements were performed with a delay time of 1 s, and thefrequency of the C–V measurements was 100 kHz.Results and DiscussionFigure 2 shows the I–V characteristics for a Pt/GaN SBD in pureN2 gas and their changes when the device was exposed to the 1% H2+ N2 mixture gas. The SBD displayed an excellent on/off ratiounder both environments; the current in the device under the 1% H2+ N2 mixture gas was enhanced compared with that in the deviceunder pure N2 gas, consistent with previous reports.14,15,18 In Fig. 2,the current in the SBD under ambient H2 gas is approximately 104times greater than that in the device under pure N2 gas. This currentgain was previously explained by the dipole model in which theapparent ΦB reduction originated from the hydrogen-induced dipolelayer formed at the metal/semiconductor interfaces;12,19 however,we have proposed a different model in which hydrogen induceschanges in the Pt/GaN interface oxide properties, resulting in theobserved increases in current in the devices under an ambienthydrogen atmosphere.14,15 The ideality factor (n) and Schottkybarrier height determined from I–V characteristics (ΦB′) werecalculated from the forward I–V curves on the basis of thethermionic emission theory (Table I).20 We then conducted C–Vmeasurements to compare the net donor concentration ND − NA ofGaN under pure N2 gas with that of GaN under 1% H2 + N2 mixturegas, where ND and NA are the donor and acceptor densities,respectively.Figure 3 shows the 1/C2 versus V data obtained from the C–Vcharacteristics for a Pt/GaN SBD under pure N2 gas and theirchanges when the device was exposed to 1% H2 + N2 mixture gas.As shown in Fig. 3, all the data are plotted on two parallel straightlines with different intercepts; that is, the line corresponding to thedata for the device under the 1% H2 + N2 mixture gas has a smallerintercept than the line corresponding to the data for the device underpure N2 gas, as we previously reported.14,15 The results in Fig. 3suggest the following two points: First, the ND − NA of the Pt/GaNSBD under 1% H2 + N2 mixture gas is the same as that under pureN2 gas because the two lines have the same slope.20 Second, theSchottky barrier height determined from the C–V characteristics(ΦB″) of the Pt/GaN SBD under 1% H2 + N2 mixture gas is smallerthan that of the device under pure N2 gas.20 We calculated the ND −NA and ΦB″ values on the basis of the data in Fig. 3; the results arereported in Table I, together with the n and ΦB′ values acquired fromFig. 2.The values in Table I are similar to those reported in our previouspaper except for the ΦB′ and ΦB″ values for the Pt/GaN SBD underpure N2;15 the reason for this discrepancy is discussed later. As notedin our previous paper,15 the data in Table I suggest the followingthree issues: First, both the ΦB′ and ΦB″ values for the Pt/GaN SBDunder 1% H2 + N2 mixture gas are lower than those for the deviceunder pure N2 gas; we assume that changes in the Pt/GaN interfaceoxide properties brought about by hydrogen reduce the ΦB′ and ΦB″values. Second, the ND − NA value for the Pt/GaN SBD under 1%H2 + N2 mixture gas is the same as that for the device under pure N2gas, as evidenced by the two parallel 1/C2 vs V curves in Fig. 3; thisvalue is roughly consistent with the doping concentration of Si intoGaN. Thus, hydrogen does not alter the electrical properties of theGaN layers, implying that hydrogen instead changes the Pt/GaNinterface oxide properties. Third, the n does not change after thedevice is exposed to 1% H2 + N2 mixture gas, meaning that thecurrent transport mechanism is the same under both of theinvestigated ambient environments. Next, we used impedancespectroscopy to investigate whether the previously proposed hy-drogen-induced dipole layer exists.Figure 4 shows Nyquist plots for a Pt/GaN SBD at 0 V in pure N2gas and in 1% H2 + N2 mixture gas. The result is consistent with ourprevious report in which hydrogen exposure was found to result in aFigure 1. Schematic of Pt/GaN SBD structure investigated in the presentstudy.Figure 2. I–V characteristics for a Pt/GaN SBD in pure N2 and the changes of the characteristics when the devices were exposed to 1% H2 + N2. Here, bluecircles represent data corresponding to pure N2 gas and red inverted triangles represent data corresponding to 1% H2 + N2 mixture gas.ECS Journal of Solid State Science and Technology, 2024 13 045002striking reduction of the radius of the semicircle in the Nyquistplot;14,15 these semicircle shapes can be explained according toequivalent RC parallel circuits representing the semiconductorspace–charge region, where R and C are the resistance andcapacitance of the semiconductor space–charge region, respectively.Table II shows the R and C values calculated from the Nyquistplots in Fig. 4. As reported previously,14,15 exposure to hydrogendrastically reduced the R value: the R value for a Pt/GaN SBD in 1%H2 + N2 mixture gas was approximately 104 times smaller than thatof the device under pure N2 gas, whereas the C value remainedalmost constant. We assume that this result is attributable tohydrogen-induced reduction of the Pt/GaN interface oxide resistancefor the following three reasons: First, as shown in Fig. 4b, a newsemicircle attributable to the hydrogen-induced dipole layer is notobserved after the Pt/GaN SBD was exposed to hydrogen; therefore,the previously proposed model does not appear to justify the data.Second, as discussed previously (Fig. 3 and Table I), the ND − NAvalue for the Pt/GaN SBD in 1% H2 + N2 mixture gas is the same asthat for the device in pure N2 gas; therefore, hydrogen exposure doesnot change the electrical properties of the GaN layers. According toour previous study involving GaN MOS capacitors,13 oxide layersbetween Pt and GaN are the most likely origin of the change in thePt/GaN interface oxide resistance because hydrogen was found to beabsorbed into the oxide layers as positive mobile charges. Third,hydrogen-induced property changes in oxides have been reported forvarious oxides, including TiO2,21 Ta2O5,22 HfO2,23 Pb(Zr,Ti)O3,24SrBi2Ta2O9,25 SrTiO3,26 and BaTiO3;27 hydrogen is known toreduce the resistance of these oxides. Hydrogen is ionized in theoxides, and electrons emitted from hydrogen contribute to thelowering of the resistance.24,26,28 We assume that the same phenom-enon occurs in the Pt/GaN interface oxide. We subsequentlyinvestigated the reaction timeframe of a Pt/GaN SBD under ahydrogen ambient atmosphere.Figure 5 shows the current for a Pt/GaN SBD at 0.15 V as afunction of time after the sample was exposed to 1% H2 + N2mixture gas. As shown in Fig. 5, the current drastically increasesafter hydrogen exposure and saturates at ∼10−8 A within a fewminutes; therefore, we recorded all of the data for the devices under1% H2 + N2 mixture gas (Figs. 2–4, and 8) after 30 min of exposureso that the hydrogen reaction had completed. Note that the saturationtime for the Pt/GaN SBD is within the same timeframe as that forpreviously reported GaN MOS capacitors.13 Next, we investigatedthe recovery characteristics of a Pt/GaN SBD after hydrogenreaction.Figure 6 shows the recovery characteristics for a Pt/GaN SBD.Note that the current at 0 min is the value in 1% H2 + N2 mixturegas after saturation (Fig. 5). When the ambient atmosphere waschanged from hydrogen to either pure N2 gas or dry air gas, thecurrent gradually reverted to its initial value observed under pure N2gas. Figure 6 shows that the nature of the ambient gas plays a criticalrole in the recovery velocity; that is, dry air gas leads to a muchfaster recovery than pure N2 gas, consistent with our previouslyreported results.14,15 This fast recovery under ambient dry air gas isattributable to the catalytic function of Pt in which hydrogen andoxygen chemically react on Pt surfaces, resulting in rapid desorptionof hydrogen from the Pt/GaN interface oxides, as previouslyreported.29,30 Next, we investigated the effect of applying a reversebias during the reversion in order to reveal the charging state ofhydrogen in oxide layers and to compare the effect of the ambientatmosphere and the bias application on the recovery rate.Figure 7 shows the recovery characteristics for a Pt/GaN SBD,where the reversion after hydrogen exposure was compared betweenan SBD under pure N2 gas and an SBD under pure N2 gas with areverse bias of −2 V applied. Note that the measurements wereTable I. Summary of n and ΦB′ values obtained from the data inFig. 2 and the ND − NA and ΦB″ values based on the data in Fig. 3.Property Value under pure N2 Value under 1% H2 + N2n 1.02 1.02ΦB′ 1.01 0.76ND − NA 2.3 × 1016 2.3 × 1016ΦB″ 1.22 0.86Figure 3. 1/C2 vs V curves for a Pt/GaN SBD under pure N2 and theirchanges when the device was exposed to 1% H2 + N2. Here, blue circlesrepresent data corresponding to pure N2 gas and red inverted trianglesrepresent data corresponding to 1% H2 + N2 mixture gas.Figure 4. Nyquist plots for a Pt/GaN SBD at 0 V (a) under pure N2 gas and (b) under 1% H2 + N2 mixture gas.ECS Journal of Solid State Science and Technology, 2024 13 045002performed six times in total for three different devices; the standarderrors are shown as the error bars with the mean values.31 Wepreviously reported that applying a reverse gate bias accelerated thereversion of GaN MOS capacitors with Al2O3 and Hf0.57Si0.43Oxgate dielectrics after hydrogen exposure.13,29 We explained thisacceleration as follows:13,29 Hydrogen absorbed into the dielectricsas positive mobile charges, and these mobile charges were driventoward the gate electrodes by the applied electric field, leading tofaster hydrogen desorption. In the case of a Pt/GaN SBD, ∼1 nm-thick crystalline native gallium oxide layers exist at the Pt/GaNinterfaces, as described earlier, instead of gate dielectrics; we assumethat hydrogen absorbed into the native gallium oxide layers inducedthe property changes in the Pt/GaN interface oxides. As shown inFig. 7, the application of a −2 V bias slightly enhanced therestoration of the device, suggesting that hydrogen can be absorbedinto the interface oxide layers as positive mobile charges, as in theoxides of MOS devices.13,29 However, the effect of the biasapplication is less prominent than in the case of the MOS devices.A possible reason for this difference might be that an electric fieldsufficiently strong to desorb hydrogen was not applied to the oxide,likely because of the poor quality of the oxide at the Pt/GaNinterfaces.17 As a result, changing the ambient atmosphere is foundto be much more effective for faster restoration. Next, we studied thechanges in the ΦB′ values of as-loaded samples using the hydrogendesorption method developed here.Figure 8 shows forward I–V characteristics for a Pt/GaN SBD inthe as-loaded condition, as measured in vacuum, and the changes inthe characteristics when the device was exposed to either 1% H2 +N2 mixture gas or dry air gas under a reverse bias of −2 V. The ΦB′values were calculated on the basis of thermionic emission theory foreach case. As shown in Fig. 8, the as-loaded Pt/GaN SBD has a ΦB′value of 0.91 eV, consistent with our previously reported results.14,15Note that the ΦB′ value of a Pt/GaN SBD in the as-loaded conditionmaintained a similar value when the ambient atmosphere waschanged from vacuum to pure N2 gas. The key issue that emergesfrom Fig. 8 is that exposing the device to dry air gas under a reversebias of −2 V increased the ΦB′ substantially compared with the ΦB′under the as-loaded condition. As shown in Fig. 8, the as-loaded Pt/GaN SBD has a ΦB′ value of 0.91 eV; thereafter, the ΦB′ valueincreases to 1.07 eV as incorporated hydrogen desorbs under the dryair gas ambient atmosphere and applied bias, suggesting thathydrogen was already absorbed into the Pt/GaN interface oxidelayers to some extent before the experiment, likely during processingand/or storage. We previously studied the hydrogen interaction ofGaN MOS capacitors with various oxides, revealing that the numberof VOs in oxides might be related to hydrogen absorption.13 In thecase of a Pt/GaN SBD, hydrogen might be trapped at VOs in theoxide layers because these oxides were found to be defective in ourprevious study.17 The data in Fig. 8 show that the ΦB′ varies in therange 0.76–1.07 eV depending on the amount of absorbed hydrogenand that this fluctuation range of ΦB′ can depend on the quality ofthe Pt/GaN interface oxides. Therefore, this method can be a usefulTable II. Summary of R and C values extracted from the Nyquistplots in Fig. 4.Parameter Value under pure N2 Value under 1% H2 + N2R [Ω] 2.2 × 1011 7.2 × 107C [pF] 3.2 3.9Figure 5. Current at 0.15 V for a Pt/GaN SBD, plotted as a function of timeafter exposure to hydrogen.Figure 6. Recovery characteristics for a Pt/GaN SBD. Here, blue circles andgreen triangles represent data corresponding to pure N2 and data corre-sponding to dry air, respectively.Figure 7. Recovery characteristics for a Pt/GaN SBD. Here, blue circlesrepresent data corresponding to pure N2 and orange triangles represent datacorresponding to pure N2 under a reverse bias of −2 V. Measurements wereperformed six times in total for three different devices; the standard errorsare shown as the error bars with the mean values.ECS Journal of Solid State Science and Technology, 2024 13 045002tool to evaluate Pt/GaN interface oxides. Moreover, as shown inTable I, the ΦB′ and ΦB″ values of Pt/GaN SBDs in pure N2 gas areslightly higher than those in our previous reports (typically approxi-mately 0.93 ⩽ ΦB′ ⩽ 0.95 and 1.17 ⩽ ΦB″ ⩽ 1.19) 14,15 because thedevice was exposed to dry air gas before the ΦB′ and ΦB″measurements in the experiment; thus, the interface oxide lackedhydrogen compared with that in the device in the as-loadedcondition. That is, the exact determination of ΦB is generally noteasy because of the nature of the incorporated hydrogen. ReportedΦB′ values of Pt/GaN SBDs, for instance, are largely scattered (0.65⩽ ΦB′ ⩽ 1.43),32–53 which might be related to the incorporatedhydrogen.ConclusionsHydrogen-induced ΦB changes of Pt/GaN SBDs fabricated onfree-standing GaN substrates were investigated using I–V, C–V,impedance spectroscopy, and I–t measurements. Ambient hydrogenwas found to lower the ΦB and reduce the R while only weaklyaffecting the n, ND − NA, and C values; these results might beattributable to changes in the properties of the Pt/GaN interfaceoxides as a result of hydrogen absorption. The changes in the ΦBvalues were reversible; specifically, the ΦB values rapidly decreasedupon exposure of the Pt/GaN SBDs to hydrogen; however, therecovery was slow. The application of a reverse bias to the Schottkyelectrodes accelerated the reversion compared with the case withouta reverse bias, suggesting that hydrogen was absorbed into theoxides as positive mobile charges. In addition, both exposure to dryair and the application of a reverse bias were found to increase theΦB′ value of the as-loaded sample from 0.91 to 1.07 eV, revealingthat the ΦB value of Pt/GaN rectifiers was kept lower as a result ofhydrogen incorporation that likely occurred during processing and/orstorage. The crystal quality of the Pt/GaN interface oxides might berelated to the amount of absorbed hydrogen, and the methoddescribed in this report might be a useful tool for evaluating theinterface oxide quality.AcknowledgmentsThis research was supported in part by JSPS KAKENHI GrantNumbers 23K03949. The authors are also grateful to the members ofthe nanofabrication facility at the National Institute for MaterialsScience.ORCIDYoshihiro Irokawa https://orcid.org/0000-0002-6531-4356References1. T. Kachi, Jpn. J. Appl. Phys., 53, 100210 (2014).2. S. Bajaj, O. F. Shoron, P. S. Park, S. Krishnamoorthy, F. Akyol, T. H. Hung,S. Reza, E. M. Chumbes, J. Khurgin, and S. Rajan, Appl. Phys. Lett., 107, 153504(2015).3. T. Oka, Jpn. J. Appl. Phys., 58, SB0805 (2019).4. S. R. Stein et al., IEEE Trans. Electron Devices (Early Access), 71, 1494 (2024).5. M. Matys, K. Kitagawa, T. Narita, T. Uesugi, J. Suda, and T. Kachi, Appl. Phys.Lett., 121, 203507 (2022).6. Y. Ichikawa, K. Ueno, T. Kondo, R. Tanaka, S. 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