Structural and electronic properties of Si- and Sn-doped (−201) β-Ga <sub>2</sub> O <sub>3</sub> annealed in nitrogen and oxygen atmospheres
Marko J. Tadjer, Jaime A. Freitas, James C. Culbertson, Marc H. Weber, E. R. Glaser, A. Mock, Nadeemullah A. Mahadik, Kenneth J. Schmieder, Eric M. Jackson, James C. Gallagher, Boris N. Feigelson, Akito Kuramata
Abstract
Abstract Single crystal (−201) β-Ga 2 O 3 substrates doped with Si and Sn have been thermally annealed in N 2 and O 2 atmospheres. Structural and electrical properties evaluation was performed via a number of experimental methods in order to quantify the effects of the doping and annealing ambient on the properties of these samples. All samples annealed in O 2 exhibited significantly lower carrier concentration, as determined by capacitance–voltage measurements. Schottky barrier diodes exhibited excellent rectification when the Ga 2 O 3 was annealed in N 2 , and significantly lower forward current using O 2 -annealed Ga 2 O 3 substrates. Deep level transient spectroscopy revealed four deep trap levels with activation energies in the range of 0.40–1.07 eV. Electron spin resonance showed a decrease in shallow donor concentration, and cathodoluminescence spectroscopy revealed nearly two orders of magnitude lower emission intensity in O 2 -annealed Ga 2 O 3 samples. Raman spectroscopy revealed a carrier concentration dependent Raman mode around 254 cm −1 observed only when the final anneal of (−201) β-Ga 2 O 3 was not done in O 2 . Secondary ion mass spectroscopy measurements revealed diffusion of unintentional Fe towards the surface of the (−201) Ga 2 O 3 samples after annealing in O 2 . Depth resolved positron annihilation spectroscopy showed an increased density of vacancy defects in the bulk region of O 2 -annealed Ga 2 O 3 substrates.