Defects at the surface of β-Ga2O3 produced by Ar plasma exposure

A Y Polyakov,N B Smirnov,P H Carey,S J Pearton,E B Yakimov,A V Chernykh,F Ren,A I Kochkova,David J Smith,In-Hwan Lee,I V Shchemerov,A A Vasilev

doi:10.1063/1.5109025

Abstract

Films of β-Ga2O3 grown by halide vapor phase epitaxy on native substrates were subjected to Ar inductively coupled plasma treatment. As a result, the built-in voltage of Ni Schottky diodes deposited on the plasma treated surfaces decreased from 1 V to −0.02 V due to the buildup of deep trap concentration in the near surface region. Deep level spectra measurements indicate a strong increase in the top ∼200 nm of the plasma treated layer of the concentration of E2* (Ec − 0.8 eV) and especially E3 (Ec − 1.05 eV) deep electron traps. Capacitance-voltage profiling with monochromatic illumination also indicated a large increase in the upper ∼100 nm of the film in the concentration of deep acceptors with optical threshold for an ionization of ∼2.3 eV and 3.1 eV. Such defects at the surface led to a significant increase in reverse current, an increase in the ideality factor in forward current, and a dramatic decrease in the diffusion length of nonequilibrium charge carriers from 450 nm to 150 nm.

Highlights

Combined with availability of excellent crystalline quality native substrates prepared by solution growth techniques,1 high quality epitaxial films, and existence of wide-bandgap ternaries of (AlxGa1−x)2O3 that can be used as barrier layers in modulation doped field effect transistors (MODFETs),1,12 there is clearly a basis for optimism about the technological prospects
We present the results of a study of deep trap spectra, persistent photocapacitance, and minority carrier diffusion length in Ga2O3 films grown by halide vapor phase epitaxy (HVPE) and exposed to Ar plasmas
Electrical characterization of the near-surface region of the samples consisted of capacitance vs frequency (C-f) at frequencies from 20 Hz to 1 MHz, capacitance-voltage (C-V) profiling at different frequencies in the dark and under illumination with high-power light emitting diodes with peak wavelengths ranging from 365 nm to 940 nm, current-voltage (I-V), microcathodoluminescence (MCL) at 300 K, and deep level transient spectroscopy (DLTS)

Summary

Introduction

The β-polytype of Ga2O3 is emerging as a potential candidate for generation high-power/high-temperature devices and solarblind UV photodetectors.1–11 The excellent intrinsic properties of this material include a wide bandgap of ∼4.8 eV, a high electrical breakdown field of ∼8 MV/cm, and a high electron saturation velocity of ∼107 cm/s.1–8 Combined with availability of excellent crystalline quality native substrates prepared by solution growth techniques,1 high quality epitaxial films, and existence of wide-bandgap ternaries of (AlxGa1−x)2O3 that can be used as barrier layers in modulation doped field effect transistors (MODFETs),1,12 there is clearly a basis for optimism about the technological prospects. Electrical characterization of the near-surface region of the samples consisted of capacitance vs frequency (C-f) at frequencies from 20 Hz to 1 MHz, capacitance-voltage (C-V) profiling at different frequencies in the dark and under illumination with high-power light emitting diodes with peak wavelengths ranging from 365 nm to 940 nm, current-voltage (I-V), microcathodoluminescence (MCL) at 300 K, and deep level transient spectroscopy (DLTS).29 The diffusion length (Ld) of nonequilibrium charge carriers at room temperature was extracted from fitting the experimentally observed dependence of the collection efficiency of the electron beam induced scitation.org/journal/apm current (EBIC) on the probing electron beam energy of the scanning electron microscope (SEM).30 Detailed descriptions of experimental setups can be found elsewhere.31,32

Results

Conclusion