Deep trap spectra of Sn-doped α-Ga2O3 grown by halide vapor phase epitaxy on sapphire

A Y Polyakov,K D Shcherbachev,S J Pearton,A A Vasilev,N B Smirnov,A V Chernykh,S I Stepanov,I V Shchemerov,A S Shikoh,A Kochkova,V I Nikolaev,A I Pechnikov,E B Yakimov

doi:10.1063/1.5094787

Abstract

Epitaxial layers of α-Ga2O3 with different Sn doping levels were grown by halide vapor phase epitaxy on sapphire. The films had shallow donor concentrations ranging from 1017 to 4.8 × 1019 cm−3. Deep level transient spectroscopy of the lowest doped samples revealed dominant A traps with level Ec − 0.6 eV and B traps near Ec − 1.1 eV. With increasing shallow donor concentration, the density of the A traps increased, and new traps C (Ec − 0.85 eV) and D (Ec − 0.23 eV) emerged. Photocapacitance spectra showed the presence of deep traps with optical ionization energy of ∼2 and 2.7 eV and prominent persistent photocapacitance at low temperature, surviving heating to temperatures above room temperature. The diffusion length of nonequilibrium charge carriers was 0.15 µm, and microcathodoluminescence spectra showed peaks in the range 339–540 nm, but no band-edge emission.

Highlights

Ga2O3 and related ternary solid solutions are promising nextgeneration materials for use in high-power devices
Pulsed halide vapor phase epitaxy (HVPE) growth of α-Ga2O3 on sapphire produces films with screw dislocation densities of (2–4) × 105 cm−2 and edge dislocations on the order of 109 cm−2.14 Doping with Sn donors in MIST CVD produced n-type material with shallow donor densities controlled from 1017–1019 cm−310,11 while undoped films prepared by either MIST CVD or by different versions of HVPE were highly resistive
We present deep trap and minority carrier transport studies for Sn-doped α-Ga2O3 films grown by HVPE on basal plane sapphire

Summary

INTRODUCTION

Ga2O3 and related ternary solid solutions are promising nextgeneration materials for use in high-power devices. Pulsed HVPE growth of α-Ga2O3 on sapphire produces films with screw dislocation densities of (2–4) × 105 cm−2 and edge dislocations on the order of 109 cm−2.14 Doping with Sn donors in MIST CVD produced n-type material with shallow donor densities controlled from 1017–1019 cm−310,11 while undoped films prepared by either MIST CVD or by different versions of HVPE were highly resistive.14 These developments have made it possible to demonstrate α-Ga2O3-based power rectifiers with attractive performance: low on-resistance of 0.1–0.4 mΩ cm and breakdown voltage of 531–855 V,10,11 the authors had to use lift-off and transfer of the grown device structures to overcome the heat control problems. Little is known about the deep traps, diffusion lengths of nonequilibrium charge carriers, and luminescence spectra of doped and undoped α-Ga2O3 films, in contrast to abundant data for the β-polytype. In undoped semi-insulating (SI) α-Ga2O3 films, deep traps near Ec − 1 eV pinning the Fermi level, deep traps with levels near Ev + 1.4 eV, and shallower electron traps near Ec − 0.3 eV and Ec − 0.6 eV, were reported. In this article, we present deep trap and minority carrier transport studies for Sn-doped α-Ga2O3 films grown by HVPE on basal plane sapphire

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSIONS