Donors and deep acceptors in β-Ga2O3

Abstract

We have studied the properties of Si, Ge shallow donors and Fe, Mg deep acceptors in β-Ga2O3 through temperature dependent van der Pauw and Hall effect measurements of samples grown by a variety of methods, including edge-defined film-fed (EFG), Czochralski (CZ), molecular beam epitaxy (MBE), and low pressure chemical vapor deposition (LPCVD). Through simultaneous, self-consistent fitting of the temperature dependent carrier density and mobility, we are able to accurately estimate the donor energy of Si and Ge to be 30 meV in β-Ga2O3. Additionally, we show that our measured Hall effect data are consistent with Si and Ge acting as typical shallow donors, rather than shallow DX centers. High temperature Hall effect measurement of Fe doped β-Ga2O3 indicates that the material remains weakly n-type even with the Fe doping, with an acceptor energy of 860 meV relative to the conduction band for the Fe deep acceptor. Van der Pauw measurements of Mg doped Ga2O3 indicate an activation energy of 1.1 eV, as determined from the temperature dependent conductivity.

Electrical properties of bulk semi-insulating β-Ga2O3 (Fe)

“…The 2.3 eV optical threshold is close to the one observed in deep level optical spectroscopy (DLOS) 19 and in photocapacitance/light C-V spectra of lightly doped ntype samples 19,21,25 and was attributed to unidentified deep acceptor states near E c À2 eV. 19 These Schottky diodes displayed a measurable capacitance at low frequencies, and the C-f characteristics showed a plateau for frequencies up to 100 Hz at 460 K [ Fig. 3(a)].…”

“…[16][17][18] The respective levels in the bandgap are expected to be close to each other and located in the vicinity of E c À0.6 eV. 16 High temperature Hall measurements on Ga 2 O 3 (Fe) showed an acceptor level at E C À0.86 eV, 19 with the material remaining weakly n-type at 400 K and not all the Fe being electrically active. Deep level transient spectroscopy (DLTS) of bulk Czochralski grown b-Ga 2 O 3 crystals revealed dominant electron traps with levels near E c À(0.74-0.82) eV, so-called E2 traps believed to be major compensating centers in the bulk material.…”

“…Deep level transient spectroscopy (DLTS) of bulk Czochralski grown b-Ga 2 O 3 crystals revealed dominant electron traps with levels near E c À(0.74-0.82) eV, so-called E2 traps believed to be major compensating centers in the bulk material. [18][19][20] For Halide Vapor Phase Epitaxy (HVPE) films, a good correlation was observed between the density of the E2 traps and the concentration of Fe, while the E2 concentration did not change upon proton irradiation. 21 This suggested that the E2 traps could correspond to the charge transfer level Fe 2þ /Fe 3þ in b-Ga 2 O 3 .…”

“…21 This suggested that the E2 traps could correspond to the charge transfer level Fe 2þ /Fe 3þ in b-Ga 2 O 3 . 20 In contrast, the density of other traps with levels close to E2, so called E2* traps, rapidly increased with proton irradiation, 19,20 indicating that native defects participate in their formation. Once the concentration of Fe doping in edge-defined film-fed grown (EFG) bulk crystals exceeded the concentration of residual donors ($2 Â 10 17 cm À3 ), the material becomes semi-insulating (SI), with a room temperature resistivity of $10 12 X cm.…”

“…These are in good agreement with the reported signature of the E2 electron trap assigned to Fe. 19 The space charge in capacitance measurements on these high-resistivity Schottky diodes is due to the difference in occupation of the E2 traps in the quasi-neutral region (these deep acceptors are partly filled with electrons coming from the shallow donors) and in the space charge region where the E2 traps are empty. The step in capacitance appears as a result of electrons on the traps not being able to follow the probing frequency.…”