REACTIVE MOLECULAR-BEAM EPITAXY OF WURTZITE GAN - MATERIALS CHARACTERISTICS AND GROWTH-KINETICS

High quality GaN layer growth by reactive molecular beam epitaxy emplo ying ammonia gas as a nitrogen source and with high growth rates (simi lar to 2 mu m/h) is described. The high crystalline quality of the lay er is evidenced by our recently reported modulation-doped field-effect transistors, GaN/AlGaN separate confinement heterostructures, GaN/AlG aN quantum wells, high quality Schottky contacts, long excitonic lifet ime, and GaN epitaxial layers that exhibit only intrinsic transitions even with the second excited states of excitonic transitions visible i n the emission spectra. The dependence of background carrier concentra tion and resistivity on substrate temperature is studied. The hexagona l nature of wurtzite GaN manifests itself as hexagonal features on the film, becoming as large as similar to 5 mu m with facets at high grow th temperatures (e.g., 800 degrees C). For low V/III ratios, large hex agonal hillocks, with highly strained regions on them, are formed due to the localized preferential growth. The photoluminescence characteri stics of the films grown with various V/III ratios are also studied. T he PL spectra were analyzed to uncover the effect of substrate tempera ture on the crystalline quality, as well as on electrical and optical properties of films. The ground and excited state excitons were seen f rom the layer grown at 800 degrees C with a growth rate of 1.2 mu m/h. The influence of two competing factors, viz., thermal activation of a mmonia and thermal desorption of Ga from the surface, on the growth ki netics was investigated. (C) 1996 American Institute of Physics.