Ultimate Performance of IB CID T2SLs InAs/GaSb and InAs/InAsSb Longwave Photodetectors for High Operating Temperature Condition

Journal of ELECTRONIC MATERIALS, Vol. 48, No. 10, 2019 https://doi.org/10.1007/s11664-019-07398-x  2019 The Author(s) U.S. WORKSHOP ON PHYSICS AND CHEMISTRY OF II-VI MATERIALS 2018 Ultimate Performance of IB CID T2SLs InAs/GaSb and InAs/ InAsSb Longwave Photodetectors for High Operating Temperature Condition P. MARTYNIUK ,1,3 K. HACKIEWICZ,1 J. RUTKOWSKI,1 and J. MIKOłAJCZYK2 1.—Institute of Applied Physics, Military University of Technology, 2 Gen. Sylwestra Kaliskiego St., 00-908 Warsaw, Poland. 2.—Institute of Optoelectronics, Military University of Technology, 2 Gen. Sylwestra Kaliskiego St., 00-908 Warsaw, Poland. 3.—e-mail: The highest performance of interband cascade detectors optimized for the longwave range of infrared radiation is investigated in this work to include decisive electric gain contribution. Presently, AIIIBV-type-II superlattice systems exhibit short carrier lifetimes limited by Shockley–Read–Hall generation–recombination processes. The maximum reported carrier lifetimes at 77 K for the InAs/GaSb and InAs/InAsSb type-II superlattices in longwave range correspond to  200 ns and  400 ns, respectively. We estimated theoretical detectivity of interband cascade detectors versus high operating temperatures, number of stages, absorber thickness, absorption coefficient and carrier lifetime; carrier lifetime were varied up to the reported value of MCT  1 ls. It has been shown that for room temperature the utmost performance–detectivity  1010 cmHz1/2/W for the optimized detector operating in the longwave range  10 lm and assuming electric gain effect could be reached. Key words: HOT, T2SLs, InAs/GaS, InAs/InAsSb, FSO INTRODUCTION Among the methods to reach higher operating temperature (HOT) conditions the proper selection of the active layer exhibiting the highest absorption coefficient and thermal generation rate ratio (a/G) must be numbered. Currently, except MCT, both type-II superlattices (T2SLs) InAs/GaSb and InAs/ InAsSb must be added to the list of the materials characterized by the highest a/G ratio. T2SLs exhibit short carrier lifetimes related to the Shockley–Read–Hall (SRH) generation–recombination (GR) mechanism. Improvement in that field was theoretically and experimentally proved by ‘‘Gafree’’ T2SLs InAs/InAsSb in comparison with T2SLs InAs/GaSb. (Received December 4, 2018; accepted June 25, 2019; published online July 16, 2019) In terms of extremely HOT conditions (up to 400 K and high frequencies 1.3 GHz) the interband cascade infrared detectors (IB CIDs) have been proving to be suitable candidates to that temperature and longwave (LWIR) range and could be implemented into free-space optical communication (Free Space Optics, FSO).1–4 IB CID contains multiple discrete absorbers designed with a thickness being thinner than the carrier diffusion length and separated by electron and hole barriers where adjacent stages are electrically connected by interband tunneling. Figure 1 shows a IB CID band structure with absorber based on the T2SLs InAs/GaSb. In an absorber, electrons are optically excited from state H1 in the valence band to state C1 in the conduction band, and then move to the left through intraband relaxation. The relaxation region is constructed with graded multiple quantum wells with discrete energy levels. Electrons return to the valence band 6093 6094 state in the adjacent absorber through interband tunneling. In terms of FSO the LWIR range is mostly explored due to the limited scattering and atmospheric turbulence in comparison to the commonly used k  1550 nm range. Currently, FSO in LWIR is dominated by MCT being temperature unstable due to the weak Hg bonds reducing the material strength, resulting in a weak mechanical properties and major difficulties in a material processing (detectivity for MCT LWIR, k  10 lm should stay within range  9 9 109–3 9 1010 Jones, while time constant 4–0.3 ns to fulfill requirements of the FSO system–detectivity and time constant stay in contradiction in optimization process).5,6 That issue could be circumvented by the IB CID with T2SLs AIIIBV active layers. In the paper the utmost detectivity of IB CID for LWIR range (k = 10 lm, Eg = 0.124 eV) and HOT conditions are discussed. Moreover, IB CID exhibits electrical gain exceeding unity that is why an influence of electrical gain on the utmost detectivity is shown.7–10 Electrical gain allows to operate with improved performance without current matching. Martyniuk, Hackiewicz, Rutkowski, and Mikołajczyk The comparison of the T2SLs: InAs/GaSb and InAs/InAsSb, assuming the characteristic parameters–absorption coefficients (a), carrier lifetimes (s) and carrier mobility (l) and dependence of the Johnson-noise limited detectivity on the absorber thickness for a different number of stages at HOT is reported. According to the calculations, the cascade detectors based on ‘‘Ga-free’’ T2SLs exhibit higher performance. Lei et al. claims that LWIR IB CID architecture has not been optimized yet but cascade detector can operate at 300 K with D* > 108 cmHz1/ 2 /W exceeding the reported values of the LWIR HgCdTe operating without cooling.11,12 ULTIMATE PERFORMANCE IB CID FOR LWIR In the simulations, the IB CID architecture for LWIR, kcut-off = 10 lm (corresponding bandgap, Eg 0.124 eV) was assumed and utmost D* was calculated. Since IB CID was proved to operate above room temperature, the utmost D* was assessed within the range 200–400 K. The detailed active layer parameters assumed in simulations include absorption coefficient, carrier lifetime, carrier Fig. 1. Schematic drawing of an IB CID photodetector with T2SLs InAs/GaSb absorber. Fig. 2. LWIR utmost detectivity for IB CID T2SL InAs/GaSb (a) and T2SL InAs/InAsSb (b) versus temperature for selected number of stages: Ns = 2, 6, 10, 20, 30. Ultimate Performance of IB CID T2SLs InAs/GaSb and InAs/InAsSb Longwave Photodetectors for High Operating Temperature Condition 6095 Table I. The nominal T2SLs InAs/GaSb and InAs/InAsSb active layers simulation parameters T2SLs Absorption coefficient (cm21) Carrier lifetime (ns) Electron effective mass Hole effective mass Electron mobility (m2/Vs) Hole mobility (m2/Vs) 3000 2000 200 400 mII = 0.0235; m^ = 0.0275 mII = 0.016; m^ = 0.018 mII = 0.0342; m^ = 79.8 mII = 0.033; m^ = 5.6 0.1 0.1 0.01 0.01 InAs/GaSb InAs/InAsSb Fig. 3. LWIR utmost detectivity for IB CID T2SL InAs/GaSb (a) and T2SL InAs/InAsSb (b) versus number of stages for selected temperatures T = 200 K, 230 K, 300 K and 380 K. mobilities and carrier effective masses (presented in Table I). Assuming equal absorber, d = 150 nm and gain contribution (see Eq. 2), the utmost detectivity reaches  5 9 109 (active layer T2SLs InAs/GaSb) and  9 9 109 Jones (T2SLs InAs/InAsSb) at 200 K while for 400 K, D*  1 9 109 and  2 9 109 Jones was estimated, which are presented in Fig. 2a and b for a selected number of stages (Ns = 2–30). lowering the external quantum efficiency. As c (...truncated)