Homoepitaxial growth of GaN thin film using radical assist sputter epitaxy method at low temperature

Abstract

We investigated unintentionally doped-gallium nitride (GaN) thin films grown on GaN template substrates at a substrate temperature of 600 °C using our developed radical assist sputter epitaxy (RaSE) method. To achieve GaN thin films with minimal defects and a smooth surface at low temperatures, it was necessary to utilize a slightly higher Ga supply compared to that in the intermediate conditions. However, the process margin for obtaining droplet-free, high-quality films using the RaSE method was notably narrow due to the formation of Ga droplets in Ga-rich conditions. These findings highlight the need to expand the process margins for effective film growth. Additionally, a significant amount of O impurities was incorporated into the GaN thin films produced by the RaSE method, a specific challenge associated with low-temperature growth. Nonetheless, these impurities could be advantageous for fabricating n-type GaN thin films and may also be useful in creating contact layers for GaN devices that require high doping concentrations but cannot withstand high temperatures. By contrast, addressing these impurities concentration in the films will expand the applications of GaN sputter technology and realize systems such as p-GaN films.