# Fileset

[03-サプリメンタル-entangledLED_supplement_20190425.pdf](https://mdr.nims.go.jp/filesets/1e5b7087-1d3a-4ab2-8882-73e34d6c46c8/download)

## Creator

[Neul Ha](https://orcid.org/0000-0002-7695-2193), [Takaaki Mano](https://orcid.org/0000-0002-6955-260X), [Takashi Kuroda](https://orcid.org/0000-0001-6445-7673), [Yoshiki Sakuma](https://orcid.org/0000-0001-6804-7217), [Kazuaki Sakoda](https://orcid.org/0000-0002-5530-3020)

## Rights

 This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Neul Ha, Takaaki Mano, Takashi Kuroda, Yoshiki Sakuma, Kazuaki Sakoda; Current-injection quantum-entangled-pair emitter using droplet epitaxial quantum dots on GaAs(111)A. Appl. Phys. Lett. 19 August 2019; 115 (8): 083106 and may be found at https://doi.org/10.1063/1.5103217.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Current-injection quantum-entangled-pair emitter using droplet epitaxial quantum dots on GaAs(111)A](https://mdr.nims.go.jp/datasets/b72a5445-a4f0-4f5c-a1be-a87afac4ed6d)

## Fulltext

Supplementary material for “Current-injection quantum-entangled-pairemitter using droplet epitaxial quantum dots on GaAs(111)A”Neul Ha, Takaaki Mano, Takashi Kuroda, Yoshiki Sakuma, and Kazuaki SakodaNational Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan(Dated: 25 April 2019)In this supplementary material, we report an atomic microscope image of the quantum dot surface(Suppl. Fig. 1), the detailed layer sequence of our diode samples (Suppl. Fig. 2), discussion about the de-vice characteristics at low temperatures, and a complete set of coincidence histograms for all polarizationcombinations (Suppl. Fig. 3).Supplementary DiscussionDiode characteristics at low temperatures. Fig-ure 1(c) in the main body of this paper shows the ELintensities of the X and XX spectral lines as a functionof bias current I for temperatures of 10 and 70 K. Theimpact of temperature on the EL intensities is summa-rized as follows: 1) The saturation intensity is roughlyfour times lower at 70 K than 10 K. A similar behavior isalso seen in Fig. 1(b). This is due to the thermal escape ofcharge carriers out of quantum dots. Since our dots havea shallow quantum confinement as low as 50 meV, theEL intensity is affected by carrier escape over the presenttemperature range. 2) With increasing I from zero, theX line at 70 K starts to appear when I ∼ 0.2 mA, and itreaches the saturation value when I ∼ 2 mA. In contrast,the X line at 10 K starts to appear when I ∼ 5 mA, morethan ten times higher than the relevant value at 70 K,and reaches saturation when I ∼ 20 mA, again, ten timehigher than the value at 70 K. Thus, we conclude that, at10 K, we need more than ten times higher injection to ob-tain the EL intensity similar to that at 70 K. This findingcontradicts a common assumption that the probability ofelectron-hole recombination is proportional to injectioncurrent. The mechanism behind this observation is re-lated to the quenching of the free carrier concentrationin the n-doped AlGaAs barrier.It is known that in n-doped III-V alloy semiconduc-tors, which include Si doped AlxGa1−xAs, deep donorlevels, often called DX centers, are formed. It is believedthat the DX level is a state of the isolated substitutionaldonor atom [1]. For Si doped AlxGa1−xAs grown bymolecular beam epitaxy, the donor activation energy EDabruptly increases with AlAs mole fraction x, and reaches150 meV at x = 0.36, which is close to the direct-indirectcrossover point (x = 0.42) [2]. Hence, the free carrier con-centration is expected to be seriously quenched at verylow temperatures. Note, we choose x = 0.25 for the bar-rier layers in order to enhance the electron concentration,though such a small mole fraction leads to shallow quan-tum confinement. Nevertheless, the free electron densityin the n-doped layer is not so high at temperatures aslow as 10 K. In this case we expect that current flowacross the intrinsic region in our p-i-n diode is governedby the conductance of holes, which are injected from thep-doped region, passed through the i -region, and recom-bined with electrons at the interface region between the i -and weakly n-doped regions. Thus, electron-hole recom-bination can hardly occur in dots unless sufficiently largecurrent is injected. At temperatures as high as 70 K, freeelectrons are activated, and recombination occurs in dotseven with a relatively low bias condition.This hypothesis is consistent with the following inde-pendent observations; (i) The X (XX) intensity depen-dence on bias current at 10 K deviates from, and is sig-nificantly lower than, the expected linear (quadratic) de-pendence at the low bias regions. (ii) The EL spectraexhibit a strong X+ line with a negligible X− line, im-plying that charge neutrality is broken in the dots, whichare mostly occupied by holes.[1] P. M. Mooney, “Deep donor levels (DX centers) in III-Vsemiconductors,” J. Appl. Phys. 67, R1 (1990).[2] T. Ishibashi, S. Tarucha, and H. Okamoto, “Si and Sndoping in AlxGa1−xAs grown by MBE,” Jpn. J. Appl. Phys.21, L476 (1982).50 nm03 nmSupplementary Figure 1. Atomic force microscopy imageof a quantum dot grown on GaAs(111)A by droplet epitaxy.The dots have a disk-like shape with an average base diameterof 40 nm and a height of 1.0 nm. They are distributed on a(111)A surface with a density of 4 × 108 cm−2. In the actualsample, the dot layer is embedded in a p-i-n diode structure.2QDs 220nm 200nm 120nm 80nm [111] n+ GaAs (111)A p-AlGaAs i-AlGaAs n-AlGaAs i-AlGaAs p-GaAs n+ GaAs (111)A p-AlGaAs i-AlGaAs n-AlGaAs i-AlGaAs QDs 100nm 100nm 120nm 120nm p-GaAs [111] (a) sample A (b) sample B Supplementary Figure 2. Layer sequence and energy dia-gram of (a) sample A and (b) sample B.�� � ������� � ����� ������������ � ����������������������
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 �� ������� � ����� �������� � ������� � ������� � ����� ������Supplementary Figure 3. Coincidence histograms for allpolarization settings at 10, 30, and 50 K (sample A). Thesedata are used to determine the fidelity to Bell pairs, shown inFig. 4(d) in the main body of this paper.