AMMONIA MOLECULAR BEAM EPITAXY OF AlGaN HETEROSTRUCTURES ON SAPPHIRE SUBSTRATES

Abstract

In order to develop a technology for the growth of Al(Ga)N-based heterostructures, the effect of different molecular beam epitaxy growth conditions on the properties of AlN and AlGaN layers was studied. The optimal conditions for the growth of AlN buffer layers were established, which made it possible to achieve a root mean square roughness as small as 0.7 nm. It was shown that an increase of AlN layer thickness leads to a decrease of density of edge dislocations, while no explicit dependence of the screw dislocation density on the layer thickness was observed. The minimal obtained dislocations density values for 1.25μm-thick AlN layer were n edges = 5.9×10 9 cm -2 and n screw = 2.2×10 7 cm -2 for edge and screw dislocations respectively. As a result of optimization of the AlGaN growth temperature, a series of 0.15μm-thick layers was grown, which showed stimulated emission at wavelengths λ = 330 nm, 323 nm, 303 nm, and 297 nm with threshold power densities of 0.7 MW/cm 2 , 1.1 MW/cm 2 , 1.4 MW/cm 2 and 1.4 MW/cm 2 , respectively. The determined optimal epitaxy conditions for AlN and AlGaN layers were used to grow the AlGaN/GaN high electron mobility transistor structure on a sapphire substrate with two-dimensional electron gas, which had a mobility of 1950 cm 2 /(Vs) at a concentration of 1.15×10 13 cm -2 . The obtained results are important for creating of nitride-based UV-emitting optoelectronic semiconductor devices, as well as high-power and high-frequency electronic devices.