Design and calculation of type-II superlattice resonant cavity-enhanced photodetector with high quantum efficiency and low dark current
Introduction
Type-II superlattice (T2SLs) is one of the alternative materials for HgCdTe because of its suppression of Auger recombination, reduction of tunneling current and the band engineering [1]. Different from the intraband transition of GaAs/AlAs quantum well materials [[2], [3], [4]], the T2SLs belong to the interband transition of minibands. Therefore, the T2SL infrared detectors belong to photovoltaic type, and the calculation of device performance parameters follows the theoretical model of photovoltaic devices. Although it has many advantages, T2SLs infrared detector still has the defects of relatively large dark current and low quantum efficiency, which limits its application in practice. The dark current of narrow-band gap semiconductor infrared detector is mainly composed of three parts: the generation-recombination (GR) dark current related to Shockley-Read-Hall (SRH) process, diffusion current related to Auger recombination, and surface leakage current [5]. The surface dark current can be reduced by passivation process. Therefore, SRH dark current is the main source of dark current in T2SLs conventional p-i-n devices, which mainly occurs in the depletion region. The device with unipolar barrier structure (such as nBn or pBp structure) consists of lightly doped absorption layer, barrier layer and heavily doped contact layer with the same doping type as the absorption layer. Because the voltage drop is mainly in the barrier layer, the SRH dark current of the absorption layer is reduced [6]. In addition, the unipolar barrier structure has self-passivation effect [6].
T2SLs infrared detector belongs to broadband detection. By adding DBR mirror, the resonant cavity-enhanced photodetector (RCE PD) can control the detection of specific wavelength to achieve narrow-band detection, and the quantum efficiency at specific wavelength is greatly improved due to the effect of resonator. The specific wavelength detection applications include CO (~4.6 μm), N2O (~4.5 μm), methane (~3.3 μm) [7]. In this paper, the infrared wavelength range of methane is studied. Theoretically, other gas detectors can be realized by changing the composition of DBR period.
At present, there are few studies on the addition of DBR mirror to T2SLs devices. These include the N-structure RCE PD proposed by Wu et al. [8], RCE PD with DBR mirror in the middle wavelength AlAsSb/GaSb T2SLs by Veronica Letka et al. [7], and DBR mirror added between the two channels of dual color long wave InAs/InAs1-xSbx/AlAs1-xSbx - based T2SLs to reduce spectral crosstalk by Yiyun Zhang et al. [9]. In this work, we first studied the photoelectric properties of nBn and pBp structure RCE PD with conventional InAs/GaSb materials. The photoelectric parameters of nBn photodetector (nBn PD), pBp photodetector (pBp PD), nBn RCE PD and pBp RCE PD are calculated. We further derived the applicable formulas of quantum efficiency and dark current in unipolar barrier structures. Compared with the devices without DBR mirror, RCE PD can significantly increase the quantum efficiency and detectivity. In Section 2, the theoretical basis of band engineering design, DBR mirror design and device parameter calculation are introduced. The device performance parameters are analyzed in Section 3. Summarize in Section 4.
Section snippets
Device design
7 ML InAs/4 ML GaSb T2SLs in middle wavelength is selected as the absorption layer and upper contact layer on account of the better properties that InAs-rich material has. According to the experimental data in Ref. [10], 100% cutoff wavelength of 7 ML InAs/4 ML GaSb T2SLs is 5 μm, and 50% cutoff wavelength is about 4 μm. The 50% cut-off wavelength of 7 ML InAs/4 ML GaSb T2SLs calculated by 8-band k·p theory is 4 μm, which is in good agreement with the reference [10]. Because of the advantage of
Results and discussion
Firstly, the performance parameters of nBn PD and pBp PD are calculated, and the influence of the thickness change of absorption region on these parameters is discussed. As the thickness of the absorption layer increases, the quantum efficiency, dark current, R0A and specific detectivity are calculated, as shown in Fig. 4, Fig. 5, Fig. 6, Fig. 7. It can be seen from Fig. 4 that the quantum efficiency of nBn and pBp devices increases gradually with the increase of the thickness of the absorption
Conclusions
In this paper, the unipolar barrier structures nBn and pBp, and the DBR mirror added to the unipolar barrier structure are designed. The quantum efficiency, dark current and specific detectivity of nBn PD, pBp PD, nBn RCE PD and pBp RCE PD are studied. At the target wavelength, the quantum efficiency and specific detectivity increase significantly, and at other wavelengths, the quantum efficiency and specific detectivity are significantly higher than those of the conventional unipolar barrier
Author statement
Yanan Du: Conceptualization, Methodology, Software, Validation, Formal analysis, Investigation, Data curation, Writing – original draft, Writing – review & editing, Visualization, Lei Wang: Same contribution as Yanan Du. Yun Xu: Resources, Writing – review & editing, Supervision, Project administration, Funding acquisition. Guofeng Song: Resources.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by National Key Research and Development Plan (No.2016YFB0402402 and No.2016YFB0400601). National Basic Research Program of China (973 Program) (No. 2015CB351902). Strategic Priority Research Program of Chinese Acacdemy of Sciences (Grant No. XDB43010000). National Science and Technology Major Project (2018ZX01005101-010). National Natural Science Foundation of China (Grant No. 61835011). National Natural Science Foundation of China (Grant No. U1431231). Key Research
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