Top-down Fabrication of Indium Arsenide Antimonide Pillars for Infrared Detection

Abstract

InSb and InAsSb pillars, which are large diameter nanowires (NWs), were investigated as an alternative infrared (IR) detector technology to HgCdTe (MCT) for tunable multispectral IR detection with optical properties manipulated by pillar diameter and pitch. Undoped InSb and InAsSb thin films were grown on undoped Si (100) substrates by molecular beam epitaxy (MBE) with a thin AlSb buffer layer. A top-down etching method was used to fabricate pillars of diameters ranging from 300 nm to 1500 nm for InSb, and 1700 nm to 4000 nm for InAsSb. Pillar arrays were analyzed optically by Fourier transform IR spectroscopy (FTIR). The InSb and InAsSb pillars produced narrow absorption peaks with wavelength ranging from 1.61 μm to 6.86 μm for InSb and 8.1 μm to 16.2 μm for InAsSb. A 100 nm increase in pillar diameter corresponded to a 0.495 μm increase in peak absorption wavelength. InSb thin films were also grown on n-type (As doped, ≤ 0.005 Ω cm) Si (100) substrates to create a p-i-n junction, with an initial 2 μm thick undoped InSb region grown directly on the substrate, and a 0.5 μm thick p-type (Be doped, 2x1019 cm-3) InSb top layer. These films were used to create two devices; an interdigitated contact photoconductor with varying finger geometry, and a photovoltaic device with square top contacts of varying area. I-V characterization demonstrated trends in current with varying finger geometry. Photocurrent measurements were obtained for both the photoconductor and photovoltaic devices under IR and solar illumination. The photocurrent values were orders of magnitude higher for the photoconductive device compared to the photovoltaic device, indicative of potential photoconductive gain. Photocurrent generation in the InSb p-i-n structure introduces the possibility of diameter-dependent photocurrent generation in etched pillar devices.