Performance modeling of MWIR InAs/GaSb/B–Al_0.2Ga_0.8Sb type-II superlattice nBn detector

Abstract

This paper reports on the unipolar medium wavelength infrared (MWIR) InAs/GaSb/B-Al 0.2 Ga 0.8 Sb type-II superlattice (T2SL) nBn detector's photoelectrical performance. In our model, the heterojunction barrier-active region (absorber) was assumed to be decisive as the contributing dark current mechanism limiting nBn's detector performance. The voltage drop analysis on the nBn structure was introduced to estimate the bias drop on the heterojunction barrier-active region. It was assumed that the contact n + -barrier heterojunction's layer has an insignificant influence on the electrical properties of the detector. In addition, a bulk-based model with an effective band gap of T2SL material has been assumed in the device modeling. Both current-voltage (I-V) and differential resistance-area product RA(V,T), characteristics of nBn's detector were found to be dominated by diffusion and generation-recombination currents in the zero-bias and the low-bias regions. At medium values of reverse voltages, the dark current was mostly affected by trap-assisted tunneling, whereas the band-to-band tunneling revealed its contribution at high values of reverse bias (V > 0.7 V). The RA(V,T) characteristics' fitting procedure allowed estimation of both diffusion and generation-recombination lifetimes as well as the trap energy level temperature dependence within T2SL energy gap. It was predicted that at T = 77 K, the RA product and detectivity reached values of 1000 cm 2 and 4 × 10 11 cm Hz 1/2 W -1 , respectively. The corresponding values at room temperature were 0.01 cm 2 and D * = 5 × 10 8 cmHz 1/2 W −1 , respectively. Finally, InAs/GaSb/B-Al 0.2 Ga 0.8 Sb T2SLs nBn's state of the art was compared to the performance of InAs/GaSb T2SLs PIN photodiodes and the HgCdTe bulk photodiodes operated at near-room temperature. It was shown that the RA product of the MWIR T2SLs nBn detector has reached a comparable level with the state of the art of the HgCdTe bulk photodiodes.

1/f Noise modeling of InAs/GaSb superlattice mid-wavelength infrared detectors

“…There are several works which deal with dark current modeling of SL-based devices (Ciura et al 2016;Czuba et al 2017;Gopal et al 2008;Martyniuk et al 2012;Nguyen et al 2004;Peng et al 2015). However, there is no electronic transport model, dedicated for superlattice-based devices so far.…”

“…The Varshni formula for the temperature dependence of the band gap E g ðTÞ ¼ 234 À 3:1 Â 10 À4 T 2 =ðT þ 270Þ [meV] is implemented with the coefficients reported for 10 ML/10 ML InAs/GaSb p-i-n detectors (Klein et al 2011). The trap-assisted tunneling I tat and the band-to-band tunneling I btb can be approximated as (Martyniuk et al 2012;Yang et al 2002):…”

“…Therefore, the calculation of detectivity requires noise measurements or at least noise estimation. Usually, in such noise estimation, only the thermal and the shot noise are taken into account if the detector is biased (Callewaert et al 2014;Khoshakhlagh et al 2010;Martyniuk et al 2012Martyniuk et al , 2016Rodriguez et al 2007). The noise consideration of a biased detector should also include the 1/f noise, which can significantly reduce detectivity in the low-frequency regime.…”

Theoretical Modeling of HOT HgCdTe Barrier Detectors for the Mid-Wave Infrared Range

“…Figure 18 shows the simulated J DARK versus the operating temperature for the MWIR BIRD HgCdTe structures (k c = 5.2 lm, T = 200 K) in comparison with experimental dark current densities for the following detectors: InAs/GaSb with AlGaSb barrier T2SL nB p n (k c = 5.4 lm, T = 230 K), InAsSb with AlAsSb barrier (k c = 5.05 lm, T = 200 K), and the HOT HgCdTe nB n n detector (x = 0.3). 17,[28][29][30] The particular significance of the incorporation of the extra barrier for carriers (n + ) in the BIRD nB n nn + structures versus the single barrier (potential majority-carrier blocking) is clearly evident from the J DARK decrease from 3 A/cm 2 to 7 9 10 À3 A/cm 2 and 40 A/cm 2 to 3 A/cm 2 for T = 200 K and T = 300 K, respectively. Proper contact layer arrangement increases the operating temperature by close to 75 K for V = 0.4 V. The absorber's p-type doping (assuming the same level of doping N D = N A = 10 14 cm À3 ) leads to a further decrease of J DARK to the level of 4 9 10 À3 A/cm 2 and 2 A/cm 2 for T = 200 K and T = 300 K, respectively.…”

“…Figure 18 shows the simulated J DARK versus the operating temperature for the MWIR BIRD HgCdTe structures (k c = 5.2 lm, T = 200 K) in comparison with experimental dark current densities for the following detectors: InAs/GaSb with AlGaSb barrier T2SL nB p n (k c = 5.4 lm, T = 230 K), InAsSb with AlAsSb barrier (k c = 5.05 lm, T = 200 K), and the HOT HgCdTe nB n n detector (x = 0.3). 17,[28][29][30] The particular significance of the incorporation of the extra barrier for carriers (n + ) in the BIRD nB n nn + structures versus the single barrier (potential majority-carrier blocking) is clearly evident from the J DARK decrease from 3 A/cm 2 to 7 9 10 À3 A/cm 2 In addition, having taken the difference in the absorber's composition into consideration, we may assume that the presented results coincide with these published by Velicu et al 17,28 Comparing the nB n n and nB n p detectors, it is clearly evident that the SRH contribution is totally suppressed for the n-type absorber structures (diffusion limited), while the p-type absorber architecture exhibits a twoslope behavior with a crossover temperature estimated at the level of T c = 227 K. Both nB n nn + and nB n pn + detectors are diffusion limited (one-slope behavior). Figure 19 compares the R 0 A (k B T/q/J s ; V = 1 mV for BIRD structures) product for nB n n, nB n nn + , and nB n nN + (the N + layer, similarly to the barrier, consists of two sublayers-the very first one fitted with a graded composition to the absorber and the second with x = 0.4) versus the values given by ''Rule 07,'' being a simple means to compare mercury cadmium telluride (MCT) IR detectors.…”