First-Principles Studies for Electronic Structure and Optical Properties of p-Type Calcium Doped α-Ga2O3.

Abhay Kumar Mondal,Mohd Ambri Mohamed,Mohd Hazrie Samat,Loh Kean Ping,Raihana Bahru,Muhammad Aniq Shazni Mohammad Haniff,Mohamad Fariz Mohamad Taib

doi:10.3390/ma14030604

Abhay Kumar Mondal, Mohd Ambri Mohamed + Show 5 more

Open Access

https://doi.org/10.3390/ma14030604

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Abstract

Gallium oxide (Ga2O3) is a promising wide-band-gap semiconductor material for UV optical detectors and high-power transistor applications. The fabrication of p-type Ga2O3 is a key problem that hinders its potential for realistic power applications. In this paper, pure α-Ga2O3 and Ca-doped α-Ga2O3 band structure, the density of states, charge density distribution, and optical properties were determined by a first-principles generalized gradient approximation plane-wave pseudopotential method based on density functional theory. It was found that calcium (Ca) doping decreases the bandgap by introducing deep acceptor energy levels as the intermediate band above the valence band maximum. This intermediate valence band mainly consists of Ca 3p and O 2p orbitals and is adequately high in energy to provide an opportunity for p-type conductivity. Moreover, Ca doping enhances the absorptivity and reflectivity become low in the visible region. Aside, transparency decreases compared to the pure material. The optical properties were studied and clarified by electrons-photons interband transitions along with the complex dielectric function’s imaginary function.

Highlights

Gallium oxides (Ga2O3) are entitled to five different polymorphs, namely α, β, γ, ε, and δ
The ultra-wide bandgap semiconductor α-Ga2O3 enables high temperature and high voltage device operation such as field-effect transistor (FET) and Schottky barrier diode (SBD). α-Ga2O3 is privillaged of superior properties such as a smaller electron effective mass, higher breakdown field, and larger Baliga figure of merit [5,6,7] which have capabilities to go beyond existing technologies to 4H–SiC (3.26 eV) [8] and GaN (3.44 eV) in the power industry [9]
Tang et al reported that the same alkaline earth metal group, calcium (Ca), plays a deep acceptor element and studied the electronic structures and optical properties of p-type Ca doped on a β-Ga2O3 first-principle calculation [17]

Summary

Introduction

Gallium oxides (Ga2O3) are entitled to five different polymorphs, namely α, β, γ, ε, and δ. The theoretically predicted Gr-I and Gr-II metals shows p-type nature by doping on Ga2O3 as reported by Tang et al [17]. In 2019, Dong et al investigated the magnesium (Mg) element substitute at the gallium site that had proven to be a good p-type conductivity in α-Ga2O3 through first-principles studies [18]. Tang et al reported that the same alkaline earth metal group, calcium (Ca), plays a deep acceptor element and studied the electronic structures and optical properties of p-type Ca doped on a β-Ga2O3 first-principle calculation [17]. Gr-IIA alkaline metal Ca doping α-Ga2O3 had reported the electronic structure and optical properties by the first-principles studies based on density functional theory (DFT). The optical absorption spectra have shown a redshift of the absorption edge towards the visible-infrared region

Computational Details

Geometrical Structures

Electron Charge Density

Band Structure and Density of States

Theoretical Description and Optical Properties

Conclusions