Emission properties of Ga2O3 nano-flakes: effect of excitation density

G Pozina,C Hemmingsson,M Forsberg,M A Kaliteevski

doi:10.1038/srep42132

Abstract

In the quest of developing high performance electronic and optical devices and more cost effective fabrication processes of monoclinic β-Ga2O3, new growth techniques and fundamental electronic and optical properties of defects have to be explored. By heating of dissolved metallic Ga in HCl in a NH3 and N2 atmosphere, nano-flake films of monoclinic β-phase Ga2O3 were grown as confirmed by XRD. From optical measurements, we observe two strong emissions. A red band peaking at ~2.0 eV and a UV band at ~3.8 eV. The band at ~2.0 eV is attributed to donor-acceptor pair recombination where the donor and acceptor level is suggested to be related to VO and nitrogen, respectively. By studying the dependence of the intensity of the UV band at 3.8 eV versus excitation density, a model is suggested. In the model, it is assumed that local potential fluctuations forming minima (maxima), where the carriers would be localized with a summarized band offset for conduction and valence band of 1 eV. The origin of the fluctuations is tentatively suggested to be related to micro-inclusions of different phases in the film.

Highlights

In the quest of developing high performance electronic and optical devices and more cost effective fabrication processes of monoclinic β-Ga2O3, new growth techniques and fundamental electronic and optical properties of defects have to be explored
The obtained Ga2O3 films were crystalized in β-phase, which was confirmed by X-ray diffraction (XRD) measurements
A typical XRD pattern is presented in Fig. 1(a), where different diffraction peaks can be well attributed to the monoclinic β-phase Ga2O3 (PDF # 41-1103)

Summary

Introduction

In the quest of developing high performance electronic and optical devices and more cost effective fabrication processes of monoclinic β-Ga2O3, new growth techniques and fundamental electronic and optical properties of defects have to be explored. One of the major bottlenecks with SiC and III-nitrides is related to very complicated and expensive processes for fabrication of large area bulk substrates[2,3,4]. This explains a huge recent interest to another wide band gap semiconductor, gallium oxide (Ga2O3), since it is possible to produce rather cheap high-quality single crystal substrates from a melt, which is a significant advantage for industrial applications. For the use as transparent electrodes, Ga2O3 films could have polycrystalline structure, which makes the synthesis processes less demanding and significantly cheaper than, for example, epitaxial growth, but the material shows usually a high level of point defects. Possible recombination mechanisms based on luminescence properties obtained by cathodoluminescence (CL) and time-resolved photoluminescence (PL) are suggested for both emission lines

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Results

Conclusion