The growth and characterization of nominally undoped Al1−<i>x</i>In<i>x</i>As grown by molecular beam epitaxy

Abstract

Al1−xInxAs films have been grown by molecular beam epitaxy (MBE) on InP substrates. Unintentionally doped material had a free electron concentration of the order of 1×1016 cm−3 when grown above 560 °C but was semi-insulating when grown below 520 °C. The effects of substrate temperature and the group V to group III flux ratio during growth on the electrical properties and on the 4 K cathodoluminescence are reported. The Auger electron spectroscopy (AES) profiles through the films show that loss of indium is detectable only at temperatures in excess of 600 °C for As4/group III flux ratios of 15–20:1. The optimum MBE growth temperature for Al1−xInxAs on InP is 580 °C. Cathodoluminescence spectroscopy was used to measure the band gap of the epitaxial layers as a function of In content for values of x between 0.46 and 0.55. Over this range, at room temperature the band gap energy was found to vary as Eg(300 K)=1.450+2.29(0.523−x) eV, while at 4 K the relation was measured to be Eg(4 K)=1.508+2.22(0.523−x) eV. The effect of strain on the band gap due to lattice mismatch between the epilayer and substrate is also considered.