Growth of undoped ZnSe on (100) GaAs by molecular-beam epitaxy: An investigation of the effects of growth temperature and beam pressure ratio

Abstract

Thin (1.5–2.5 μm thick) ZnSe films have been grown on (100) GaAs substrates by molecular-beam epitaxy to investigate the effects of growth conditions on film properties. A ‘‘growth matrix’’ was generated by systematically adjusting the growth temperature (TG) through 250, 300, 350 and 400 °C while setting the Zn-to-Se beam pressure ratio at 1/4:1, 1/2:1, 1:1, and 2:1. Reflection high-energy electron diffraction (RHEED) patterns monitored during growth showed surface reconstructions which were characteristic of either Zn- or Se-stabilized growth. In addition to the transition between the two surface reconstructions, a transition from streaky to spotty RHEED patterns was discovered. Both transition lines were mapped onto growth parameter space and their intersection provides a unique reference point in growth space. Low-temperature photoluminescence, optical microscopy and Hall measurements were used to characterize the samples in this growth matrix study and these results were found to be related to the RHEED transitions. One narrow region of growth space was found to produce samples with intense, narrow near-band-edge peaks and small deep-level intensity. Although it was still n type, one of the samples with growth conditions in this region was measured to have a carrier concentration less than 5.6×1015 cm−3 and a peak mobility greater than 7150 cm2/V s.