Liquid-Metal-Enabled Synthesis of Aluminum-Containing III-Nitrides by Plasma-Assisted Molecular Beam Epitaxy

TL;DR

This paper introduces a liquid-metal-enabled molecular beam epitaxy method to grow high-quality, highly doped aluminum-containing nitride films, overcoming previous challenges in crystalline quality and doping efficiency for optoelectronic applications.

Contribution

It presents a novel liquid-metal-assisted MBE technique that improves the growth of aluminum-rich nitride films with high crystalline quality and doping levels, distinct from conventional liquid epitaxy.

Findings

Achieved high p-type doping up to 6×10^{17} cm^{-3} in AlGaN films.

Demonstrated high crystalline quality and atomically smooth heterostructures.

Enabled growth of aluminum-rich nitrides with improved properties for device applications.

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 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 \times 10$$^{17}$ cm$^{-3}$ and n-type doping of up to $1 \times 10$$^{20}$ cm$^{-3}$ in Al$_{0.7}$Ga$_{0.3}$N 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.