Characterization of HgCdTe Films Grown on Large-Area CdZnTe Substrates by Molecular Beam Epitaxy

Abstract

Recent advances in growth of Hg_1−x Cd _x Te films on large-area (7 cm × 7.5 cm) CdZnTe (CZT) substrates is presented. Growth of Hg_1−x Cd _x Te with good uniformity on large-area wafers is achieved using a Riber 412 molecular beam epitaxy (MBE) tool designed for growth of Hg_1−x Cd _x Te compounds. The reactor is equipped with conventional CdTe, Te, and Hg sources for achieving uniform exposure of the wafer during growth. The composition of the Hg_1−x Cd _x Te compound is controlled in situ by employing a closed-loop spectral ellipsometry technique to achieve a cutoff wavelength (λ _co) of 14 μm at 78 K. We present data on the thickness and composition uniformity of films grown for large-format focal-plane array applications. The composition and thickness nonuniformity are determined to be <1% over the area of a 7 cm × 7.5 cm wafer. The films are further characterized by Fourier-transform infrared spectroscopy, optical microscopy, and Hall measurements. Additionally, defect maps show the spatial distribution of defects generated during the epitaxial growth of the Hg_1−x Cd _x Te films. Microdefect densities are in the low 10³ cm⁻² range, and void defects are below 500 cm⁻². Dislocation densities less than 5 × 10⁵ cm⁻² are routinely achieved for Hg_1−x Cd _x Te films grown on CZT substrates. HgCdTe 4k × 4k focal-plane arrays with 15 μm pitch for astronomical wide-area infrared imagers have been produced using the recently developed MBE growth process at Teledyne Imaging Sensors.