Two-Step Deposition of an Ultrathin GaN Film on a Monolayer MoS Template.

Ultrathin gallium nitride (GaN) application can be profoundly influenced by its quality, especially the issue of amorphous interfacial layers formed on conventional substrates. Herein, we report a two-step deposition of an ultrathin GaN film via the plasma-enhanced atomic layer deposition (PEALD) technique on a mono-MoS template over a SiO/Si substrate for quality improvement, by starting the deposition temperature at 260 °C and then ramping it to 320 °C. It was found that a lower initiating deposition temperature could be conducive to maintaining the mono-MoS template to support the subsequent growth of GaN. Compared to the control group of one-step high-temperature deposition at 320 °C, ideal layer-by-layer film growth is achieved at the low temperature of the two-step method instead of island formation, leading to the direct crystallization of GaN on the substrate with a rather sharp interface. Structural and chemical characterizations show that this two-step method produces a preferred [0001] orientation of the film originating from the interface region. Additionally, the improved two-step ultrathin GaN displays a smooth surface roughness as low as 0.58 nm, a low oxygen impurity concentration of 3.6%, and a nearly balanced Ga/N stoichiometry of 0.95:1. Our work paves a possible way to the feasible fabrication of ultrathin high-quality PEALD-GaN, and it is promising for better performance of relevant devices.