Study of wet etching on long-wavelength InAs/GaSb Type-II superlattices

Abstract

In the specialized arena of long-wave infrared (LWIR) detectors, the InAs/GaSb type-II superlattice (T2SL) has risen in prominence, capturing the keen interest of researchers and engineers. This is primarily because of its unique set of superior properties that contribute to its effectiveness in sensing and detecting long-wave infrared radiation. The current study delves into the realm of wet chemical etching for fast and cost-effective InAs/GaSb type-II superlattice LWIR detectors. The procedure involved a meticulous and systematic variation of the concentrations of key chemicals like citric acid, hydrogen peroxide, and phosphoric acid. The aim of this study was to perform single-variable experiments to elucidate the influence of different component ratios on the etching rate, surface roughness, device sidewall morphology, and the characteristics of surface deposits in etched long-wave nBn structure device. To visually capture the changes in the mesa's sidewall morphology, scanning electron microscopy (SEM) was employed. Energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) were utilized to analyze the reaction products on the sidewall and surface. The results from these experiments were compelling. They revealed that when the ratio of H₂O₂ to H₃PO₄ was 1: 1, the surface roughness of the devices after etching was approximately 10 nm, which is considered ideal. Moreover, the sidewall etch angle in this condition approached nearly 70°, suggesting a well-defined etching pattern. An interesting phenomenon is that when the same H₂O₂: H₃PO₄ = 1:1, most of the insoluble Sb₂O₃ deposits can be dissolved with citric acid well. This process resulted in a relatively ideal mesa morphology, meaning the mesa structures were clean and well-defined, which is crucial for efficient detection.