Analysis of AlGaAs/GaAs/InGaAs n-type step multiple quantum wells for the optimization of normal incident absorption

Abstract

The response to normal incident radiation in n-type Γ square quantum wells (QWs) is generally expected to be very small because, in the framework of the effective mass model, the parity selection rule of the envelope wavefunctions essentially forbids intersubband transitions induced by transverse electric polarized radiation. This problem can be overcome by employing an asymmetrical QW. In this paper, the effect of asymmetry, and the result of band mixing with the p-like valence and conduction bands due to the truncation of bulk crystal periodicity, of an n-type AlGaAs/GaAs/InGaAs step multiple QW, are analysed using a new 14-band k · p model with envelope function approximation. The structural and material parameters of the device are varied to study the probability density distributions of the ground state and first excited state wavefunctions, and their effect on the response of the device to transverse electric (TE) and transverse magnetic (TM) excitations. From the analysis, it is found that a step multiple QW optimized for absorption of TE mode radiation should have a wide GaAs step and a deep InGaAs well, subjected to the constraints of the material growth and fabrication process of the device. It is also found that, despite the efforts of improving the normal incidence absorption via step well optimization, the TE absorption as predicted using the 14-band k · p model remains less than 1% of the TM absorption.