Vapor-liquid-solid (VLS) growth of lead chalcogenide thin films for infrared sensing applications

Abstract

Infrared sensors are used in a variety of applications, from gas and moisture analysers, to human body detection to spectrophotometers. Available IR technology falls on two ends of the spectrum: state-of-art photon detectors are high-quality but expensive and cumbersome due to the need for cryogenic cooling, while thermal detectors are inexpensive but not very sensitive. The goal of this project is to develop materials for uncooled IR sensors with improved performance. Lead selenide (PbSe) detectors are direct narrow band gap materials that have shown promise for relatively inexpensive IR sensing with modest cooling requirements. Adapting the vapour-liquid-solid (VLS) growth mechanism traditionally used for growing nanowires to growing PbSe thin films circumvents the very slow adsorption of a gas phase into a solid surface by introducing a catalytic liquid alloy phase, while simultaneously retaining the stoichiometric control, simplicity, and economy of vapor phase growth. We have set the stage for further experimentation by demonstrating that we can attain a single phase PbSe thin film via VLS growth on an epitaxially matched substrate. We have explored the effects of VLS growth vs. vapor growth on crystal quality as well as the factors that influence diffusion and nucleation rates, such as film thickness, growth temperature, and the presence of a capping layer.