Growth of millimeter wave AlN/GaN heterostructures by MOCVD

Abstract

The influences of growth temperature on crystalline quality and electrical properties of thin barrier AlN/GaN heterostructures were studied by metal organic chemical vapor deposition (MOCVD). It is found that the high growth temperature (≥1100 °C) is beneficial to improve the crystalline quality of the AlN barrier layer, but increases the defect density in the GaN buffer layer. The AlN/GaN hetero-interface quality was deteriorated when high-temperature AlN barrier layer was grown upon low-temperature GaN buffer layer, resulting in a reduction of electron mobility. In addition, the growth temperature of the GaN cap layer affects the stress evolution of wafer during the cooling process, which influences the wafer bowing and electrical properties. By optimizing the growth temperature of each functional layer, the GaN/AlN/GaN heterostructure with a low defect density and a smooth surface is obtained. The electron mobility at room temperature is 1549 cm2/(V·s) with a sheet resistance value of 504.8 Ω/□, and the root mean square (RMS) of surface roughness is 0.322 nm. Based on the as-grown GaN/AlN/GaN heterostructure, a GaN power MMIC was fabricated, offering an output power of 15 dBm (31.6 mW) and power added efficiency (PAE) of 9.3% at 146 GHz.