Structural and electronic properties of Si- and Sn-doped (−201) β-Ga₂O₃ annealed in nitrogen and oxygen atmospheres

Abstract

Single crystal (−201) β-Ga2O3 substrates doped with Si and Sn have been thermally annealed in N2 and O2 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 O2 exhibited significantly lower carrier concentration, as determined by capacitance–voltage measurements. Schottky barrier diodes exhibited excellent rectification when the Ga2O3 was annealed in N2, and significantly lower forward current using O2-annealed Ga2O3 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 O2-annealed Ga2O3 samples. Raman spectroscopy revealed a carrier concentration dependent Raman mode around 254 cm−1 observed only when the final anneal of (−201) β-Ga2O3 was not done in O2. Secondary ion mass spectroscopy measurements revealed diffusion of unintentional Fe towards the surface of the (−201) Ga2O3 samples after annealing in O2. Depth resolved positron annihilation spectroscopy showed an increased density of vacancy defects in the bulk region of O2-annealed Ga2O3 substrates.

Raman Spectroscopic Characterization of Chemical Bonding and Phase Segregation in Tin (Sn)-Incorporated Ga2O3

“…The Raman spectra were analyzed for crystal structure and crystal symmetry to further understand the chemical purity and bonding within Ga–Sn–O. For x = 0.0, the sample exhibits the characteristic Raman peaks related to intrinsic monoclinic β-Ga 2 O 3 . , As Sn concentration increases, the Raman data show the peak evolution and intensity variation, which is fully dependent on the Sn-content. It appears that a secondary Sn-alloyed β-Ga 2 O 3 phase (Ga–Sn–O) forms, where Ga atoms are partially substituted by Sn atoms, while Ga–Sn–O + SnO 2 composite formation occurs at higher values of Sn­( x ).…”

Impact of electron irradiation on semi-insulating and conductive β-Ga2O3 single crystals

“…In addition, a mode around 258 cm −1 was also observed in Si-doped samples, which has been correlated to the presence of a sufficient concentration of donors such as Si and Sn, and to the sample having undergone thermal annealing in a non-O 2 atmosphere. 27 Although previous literature suggested this mode is carrier concentration dependent, 27 no obvious change of the peak intensity was found before and after the electron irradiation.…”

“…In addition, a mode around 258 cm À1 was also observed in Si-doped samples, which has been correlated to the presence of a sufficient concentration of donors such as Si and Sn, and to the sample having undergone thermal annealing in a non-O 2 atmosphere. 27 Although previous literature suggested this mode is carrier concentration dependent, 27 no obvious change of the peak intensity was found before and after the electron irradiation. In b-Ga 2 O 3 , three ESR peaks with g factors of approximately 1.96, 1.99, and 2.003 can be expected, and these have been assigned to shallow donors, singly ionized oxygen vacancy, and free electron/V Ga , respectively.…”

Ga vacancies in β-Ga2O3: split or not?

“…17,31,32) Another approach is to make a detailed analysis of the positron diffusion lengths in slow positron experiments. [33][34][35] This gives the possibility to interpret the changes in terms of defect concentrations, but also there the anisotropy needs to be acknowledged. It is not yet known whether the quasi-one-dimensional positron state in the β-Ga 2 O 3 lattice causes anisotropy in positron diffusion as well.…”