From Amorphous to β-Gallium Oxide: Practical Implementation of Energetics Considerations in Process Design and Optimization

Abstract

Gallium oxide (Ga2O3) is a wide bandgap material (bandgap ~4.0 eV – 5.2 eV) with a large breakdown field that has considerably high figures of merit (FOM) in power handling compared to other wide bandgap semiconductor materials in use today (such as GaN and SiC) [1, 2]. Gallium oxide is also expected to expand the operating spectral range of optoelectronic devices to deep UV.Properties of gallium oxide depend on its crystal structure; amorphous [3, 4] as well as different crystalline forms [5] of this material have been used in electronic and optoelectronic devices. Among gallium oxide crystalline polymorphs, β-Ga2O3 has attracted the most attention because it is the most stable gallium oxide polymorph and, therefore, can ultimately be obtained by heating other gallium oxide polymorphs (and even amorphous gallium oxide) at sufficiently high temperatures (ca. 550°C and above); this polymorph can also be obtained from the melt at high temperatures (ca. 1800°C) using bulk crystal growth techniques [1, 6]. In the thin film form, growing high quality β-Ga2O3 is only possible on very limited substrates (e.g., β-Ga2O3 native substrate and sapphire) while having to carefully choose very specific process conditions based on each process and the instrument being used.In this work, we present strategies and guidelines, based on energetics considerations, that make it possible to design epitaxial deposition processes that achieve β-Ga2O3 thin films at low temperatures (< 300°C). We use the atomic layer deposition (ALD) technique to achieve dense and pinhole-free films of amorphous gallium oxide. Then, we revise the deposition process conditions step-by-step so that the energetics of the process can lead us to obtain high quality epitaxial β-Ga2O3 at low temperatures while not being limited to β-Ga2O3 native substrates or very specific (or instrument-dependent) process conditions. The results presented in this work facilitate the implementation of Ga2O3 in next generation wide bandgap electronic devices.