Reactive molecular beam epitaxy of wurtzite GaN: Materials characteristics and growth kinetics

Abstract

High quality GaN layer growth by reactive molecular beam epitaxy employing ammonia gas as a nitrogen source and with high growth rates (∼2 μm/h) is described. The high crystalline quality of the layer is evidenced by our recently reported modulation‐doped field‐effect transistors, GaN/AlGaN separate confinement heterostructures, GaN/AlGaN quantum wells, high quality Schottky contacts, long excitonic lifetime, and GaN epitaxial layers that exhibit only intrinsic transitions even with the second excited states of excitonic transitions visible in the emission spectra. The dependence of background carrier concentration and resistivity on substrate temperature is studied. The hexagonal nature of wurtzite GaN manifests itself as hexagonal features on the film, becoming as large as ∼5 μm with facets at high growth temperatures (e.g., 800 °C). For low V/III ratios, large hexagonal hillocks, with highly strained regions on them, are formed due to the localized preferential growth. The photoluminescencecharacteristics of the filmsgrown with various V/III ratios are also studied. The PL spectra were analyzed to uncover the effect of substrate temperature on the crystalline quality, as well as on electrical and optical properties of films. The ground and excited state excitons were seen from the layer grown at 800 °C with a growth rate of 1.2 μm/h. The influence of two competing factors, viz., thermal activation of ammonia and thermal desorption of Ga from the surface, on the growth kinetics was investigated.