# The Formation of an Interface and Its Energy Levels Inside a Band Gap in InAs/GaSb/AlSb/GaSb M-Structures

## TL;DR

The paper explores how interface energy levels in InAs/GaSb/AlSb/GaSb M-structures affect optical absorption in materials for infrared applications.

## Contribution

The study identifies a novel energy level within the band gap caused by InSb-like interfaces in M-structures.

## Key findings

- An additional energy level within the band gap is found to originate from InSb-like interfaces.
- Optical absorption increases significantly under optimized interface thickness and temperature.
- HRXRD confirms the high crystal quality of the fabricated M-structures.

## Abstract

We studied specially designed InAs/GaSb/AlSb/GaSb M-structures, a type-II superlattice (T2SL), that can serve as active materials for short-wavelength infrared (SWIR) applications. To obtain the dispersion relation of the investigated M-structures, k·p perturbation theory based on the eight-band model implemented in the nextnano++ v1.18.1 (nextnano GmbH, Munich, Germany) software was used. Numerical band-gap engineering and dispersion calculations for the investigated M-structures (composed of 6/1/5/1 monolayers, with InSb interfaces included) revealed the presence of an additional energy level within the energy gap. This energy level originates from the InSb-like interfaces and does not appear in structures with different layer or interface thicknesses. Its properties strongly depend on interface thickness, temperature, and strain. Numerical calculations of the probability density function |Ψ|2, absorption coefficients, and optical absorption spectra at varying temperatures demonstrate that, under specific conditions, such as an optimised interface thickness and temperature, optical absorption increases significantly. These theoretical results are based on structures fabricated using molecular-beam epitaxy (MBE) technology. High-resolution X-ray diffraction (HRXRD) measurements confirm the high crystallographic quality of these M-structures.