Liquid-metal-enabled synthesis of aluminum-containing III-nitrides by plasma-assisted molecular beam epitaxy

Abstract

Nitride films are promising for advanced optoelectronic and electronic device applications. However, some challenges continue to impede development of high aluminum-containing devices. The two major difficulties are growth of high crystalline quality films with aluminum-rich compositions, and efficiently doping such films p-type. These problems have severely limited the use of aluminum-rich nitride films grown by molecular beam epitaxy. A way around these problems is through use of a liquid-metal-enabled approach to molecular beam epitaxy. Although the presence of a liquid metal layer at the growth front is reminiscent of conventional liquid phase epitaxy, this approach is different in its details. Conventional liquid epitaxy is a near-thermodynamic equilibrium process which liquid-metal assisted molecular beam epitaxy is not. Growth of aluminum-rich nitrides is primarily driven by the kinetics of the molecular vapor fluxes, and the surface diffusion of adatoms through a liquid metal layer before incorporation. This paper reports on growth of high crystalline quality and highly doped aluminum-containing nitride films. Measured optical and electrical characterization data show that the approach is viable for growth of atomically smooth aluminum-containing nitride heterostructures. Extremely high p-type doping of up to 6 × 1017 cm−3 and n-type doping of up to 1 × 1020 cm−3 in Al0.7Ga0.3N films was achieved. Use of these metal-rich conditions is expected to have a significant impact on high efficiency and high power optoelectronic and electronic devices that require both high crystalline quality and highly doped (Al,Ga)N films.