Indium doping of CdTe and Cd1-xZnxTe by molecular-beam epitaxy: Uniformly and planar-doped layers, quantum wells, and superlattices

Abstract

CdTe and Cd1-xZnxTe layers and microstructures were doped with indium donors during their growth at low temperatures (200-220°C) by molecular-beam epitaxy under Cd overpressure. Uniform and planar doping of layers and local doping of quantum wells and superlattices are presented. Characterization techniques include secondary-ion mass spectroscopy (SIMS), capacitance-voltage and Hall-effect measurements, optical spectroscopy, x-ray double diffraction, and x-ray photoelectron spectroscopy. In the range of indium concentrations 2×1016-1×1018 cm-3, the donor activation efficiency is 100% for uniform doping. A low-temperature carrier mobility of up to 5300 cm2/V s is obtained. The highest measured carrier concentration is 1.3×1018 cm-3; at a higher doping level, strong compensation occurs, related to dopant migration and cadmium vacancy formation. Planar doping also yields ≊100% activation efficiency for moderate values of sheet density (≊1011 cm -2) but has the same limit of about 1018 cm-3 for total carrier concentration. High-structural-quality planar-doped quantum wells and superlattices are obtained. Good localization of dopant is demonstrated by SIMS at low sheet density but at high concentration substantial migration of indium occurs.