A comprehensive set of simulation tools to model and design high-performance Type-II InAs/GaSb superlattice infrared detectors

Abstract

In this work, the electronic band structure of the InAs/GaSb superlattice (SL) is calculated using a commercial 8-band k⸳p solver and the electrical performance of longwave nBp device structure evaluated with Atlas from Silvaco software. By taking into account an InSb interface layer and the interface matrix (formulated by P.C. Klisptein), the model can predict the measured energy band gap of different InAs/GaSb SLs having different period composition and thickness (7/4, 10/4, 12/4, 14/4 and 14/7 SLs) within an error corresponding to the ± deviation range. The effective mass is then extracted from the electronic band structure calculation and discussed for numerous SL designs. In particular, we compare a 14/7 SL and a 12/2 SL having an energy band gap equal to 0.122 and 0.118 eV at 77K, respectively. The electron-hole wavefunction overlap for the 12/2 SL has been estimated to be ~74%, which is almost twice the value calculated for the 14/7 SL (~40%). This arises from the delocalization of carriers in a thinner SL period also leading to smaller carrier effective masses in the 12/2 SL. The dark-current of a nBp structure has been calculated for both SLs. For the 14/7 SL, the dark-current level has been found to be higher by a factor of over 3 than the Rule07 benchmark, whereas for the 12/2 SL, it is lower by a factor of 0.77, demonstrating that the SL design can be used to improve the device performances.

Carrier localization and miniband modeling of InAs/GaSb based type-II superlattice infrared detectors

“…It is already demonstrated in several earlier works that the interface region can ideally be of InSb or GaAs (or their higher order compounds) type based on the growth condition [28,32]. However, in most of the cases, InSb is the preferred choice as far as the accurate band modeling is concerned [67].…”

“…In our simulation, we assume a fixed interface layer thickness (t int ) of 0.5 ML which is symmetric with respect to the junction. Although a few previous studies considered the interface thickness to be somewhere between 0.5 and 1 ML or within and around 10% of the InAs layer thickness [24,67], it should be kept in mind that the InSb interface cannot be so thick such that it forms a quantum-well region at the junction of the two constituent SL materials or cannot be so thin such that it fails to capture and compensate the strain effects. Thus, a unit cell of the periodic structure as shown in figure 1 is formed with the arrangement {InSb(t int /2)-InAs(t InAs − t int )-InSb(t int )-GaSb(t GaSb − t int )-InSb(t int /2)} which corresponds to the period of thickness d = t InAs + t GaSb .…”

“…Since the tunneling probability has an exponential dependence on the carrier effective masses, the calculation of effective mass as a function of the layer thicknesses holds much significance. In InAs/GaSb SL, effective masses are less influenced by the interaction between the valence and conduction bands as they mainly depend on the electron (hole) wave function overlap between the adjacent InAs (GaSb) layers [67] and m * h with respect to t InAs and t GaSb . It can be seen that for the 8 ML/8 ML configuration, m * e = 0.0245 which is closer to that of the bulk InAs value and m * h = 0.16, way lesser than both bulk InAs and GaSb.…”

“…have been considered [25,26,67]. Here, the interface parametersα and β have been set to 0.2 eVÅ and the diagonal fitting parameters Ds, Dx, Dz are respectively taken as 3 eVÅ, 1.3 eVÅ and 1.1 eVÅ [24].…”

Flexibility of Ga-containing Type-II superlattice for long-wavelength infrared detection

“…The material parameters for InAs, GaSb and InSb binaries used for the k⸳p band structure calculation are given in Table 1 of Ref. [33].…”