Carrier removal rates in 1.1 MeV proton irradiated α-Ga₂O₃ (Sn)

Abstract

Films of α-Ga2O3 (Sn) grown by Halide Vapor Phase Epitaxy (HVPE) on sapphire with starting net donor densities in the range 5×1015- 8.4×1019 cm-3 were irradiated at room temperature with 1.1 MeV protons to fluences from 1013 -1016 cm-2. For the lowest doped samples, the carrier removal rate was ~35 cm-1 at 1014 cm-2 and ~1.3 cm-1 for 1015 cm-2 proton fluence. The observed removal rate could be accounted for by the introduction of deep acceptors with optical ionization energies of 2 eV, 2.8 eV and 3.1 eV. For doped samples doped at 4x1018 cm-3, the initial electron removal rate was 5×103 cm-1 for 1015 cm-2 proton fluence and ~300 cm-1 for 1016 cm-2 proton fluence. The same deep acceptors were observed in photocapacitance spectra, but their introduction rate was orders of magnitude lower than the carrier removal rate. For the heaviest doped samples, an electron removal rate could be measured only after irradiation with the highest proton fluence of 1016 cm-2 and was close to that measured for the 4×1018 cm-3 sample after exposure to the same fluence. Possible reasons for the observed behavior are discussed and radiation tolerances of lightly doped α-Ga2O3 films is higher than for similarly doped β-Ga2O3 layers.

Proton damage effects in double polymorph γ/β-Ga2O3 diodes

“…Interestingly, the spectral dependence of photocapacitance is not all that different from the spectral dependence in β-Ga 2 O 3 . 9,32,34,36 Mind also that the peak photocurrent value at −3 V after irradiation decreased only by about 2 times (Fig. 4).…”

“…For comparison, for Si and SiC diodes having similarly low carrier concentrations in the active diode region, degradation was already present for ∼5 × 10 11 and ∼7 × 10 12 cm −2 1 MeV proton fluences, respectively. 34 The present demonstration of the radiation tolerance of γ/β-Ga 2 O 3 samples paves the way for further detailed studies of double polymorph γ/β-Ga 2 O 3 diodes, which are certainly necessary to shed the light on the mechanisms of the donor activation upon the hydrogenation in γ-Ga 2 O 3 as well as to explain the evolution and interplay between shallow and deep levels upon the irradiation.…”

“…9,32 Similar centers are observed in other Ga 2 O 3 polymorphs. 9,30,34–36 The optical threshold for these persistent transitions is around 2 eV. After 2.3 eV the contribution of persistent capacitance centers becomes less pronounced.…”

“…33 One also has to perform C – V measurements under monochromatic illumination to detect and characterize very deep donors and acceptors throughout the width of the bandgap, and to complement DLTS/ODLTS measurements with their current CDLTS/PICTS counterparts. 32,34–36…”

“…Detailed descriptions of the electrical measurements setups and proton irradiation setup can be found elsewhere. 33–37…”