Advancement of optoelectronic and high-power devices is tied to the development of wide band gap materials with excellent transport properties. However, bipolar doping (n-type and p-type doping) and realizing high carrier density while maintaining good mobility have been big challenges in wide band gap materials. Here P-type and n-type conductivity was introduced in β-Ga2O3, an ultra-wide band gap oxide, by controlling hydrogen incorporation in the lattice without further doping. Hydrogen induced a 9-order of magnitude increase of n-type conductivity with donor ionization energy of 20 meV and resistivity of 10 -4 Ω.cm. The conductivity was switched to p-type with acceptor ionization energy of 42 meV by altering hydrogen incorporation in the lattice. Density functional theory calculations were used to examine hydrogen location in the Ga2O3 lattice and identified a new donor type as the source of this remarkable n-type conductivity. Positron annihilation spectroscopy confirmed this finding and the interpretation of the results. This work illustrates a new approach that allows a tunable and reversible way of modifying the conductivity of semiconductors and it is expected to have profound implications on semiconductor field. At the same time it demonstrates for the first time p-type and remarkable n-type conductivity in Ga2O3 which should usher in the development of Ga2O3 devices and advance optoelectronics and high-power devices.

Electronic defects with shallow and deep levels in β-Ga2O3 single crystals were investigated by thermoluminescence (TL) spectroscopy. Undoped, Fe-doped, Sn-doped, and Mg-doped β-Ga2O3 single crystals grown by different methods were studied, and thermal activation energies of defects were calculated using the initial rise method. Hall-effect measurements and optical absorption spectroscopy were performed to determine the electrical transport properties and optical bandgaps. It was found that the dopants do not have any effect on the bandgap energy, which is important for comparing the trap levels in the samples. Three deep trap levels were found in the undoped crystals; the activation energy, ED, and concentration of defect centers for all of them have slightly changed after doping with Fe and Mg. Fe doping induced an additional defect center with activation energy of 0.62 eV. The measurements revealed the absence of TL emission in Sn doped crystals indicating that Sn doping may quench luminescence centers or modified some original electronic defects to inactive electron traps. The second interpretation “decrease of traps” may align with the successful incorporation of Sn as a donor and the high conductivity of Sn doped crystals revealed from Hall-effect measurements. This work also illustrates that the semi-insulating characteristics of Fe and Mg doped Ga2O3 are associated with the increase of the concentration of original traps in the crystal as well as the formation of new electron traps acting as deep acceptors. Recombination centers in all crystals are assumed to be associated with iron impurities.

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Intrinsic and extrinsic point defects often act as electron traps in oxide-based semiconductors and significantly impact their electrical and optical properties. Here, we show how to measure the density, energy level, and trapping cross section of the compensating acceptors that act as electron traps in Ga2O3 films, and we introduce the sheet trap number or the sheet compensating acceptor number as an essential parameter to fully describe the electrical transport properties of semiconductors. Si-doped β-Ga2O3 thin films were fabricated homoepitaxially by metalorganic chemical vapor deposition and studied by thermally stimulated luminescence spectroscopy, temperature dependent Hall-effect measurements, and secondary ion mass spectroscopy to investigate the compensating acceptor defects responsible for suppressing conductivity in the films. A deep level defect of energy in the range of 0.50–0.65 eV was identified as a compensating acceptor. The correlation between the electrical properties and its concentration and characteristics was established. This work shows how to quantify the density of compensating acceptors in semiconductors and directly relate it to the electrical transport properties, which should significantly advance the development of semiconductors and devices.

Monoclinic gallium oxide (β-Ga2O3) is attracting intense focus as a material for power electronics, thanks to its ultra-wide bandgap (4.5–4.8 eV) and ability to be easily doped n-type. Because the holes self-trap, the band-edge luminescence is weak; hence, β-Ga2O3 has not been regarded as a promising material for light emission. In this work, optical and structural imaging methods revealed the presence of localized surface defects that emit in the near-UV (3.27 eV, 380 nm) when excited by sub-bandgap light. The PL emission of these centers is extremely bright—50 times brighter than that of single-crystal ZnO, a direct-gap semiconductor that has been touted as an active material for UV devices.