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Activation of implanted donors into a highly-resistive, nitrogen-doped homoepitaxial β-Ga2O3 has been investigated. Nitrogen acceptors with the concentration of ∼1017 cm−3 were incorporated during epitaxial growth yielding low-doped (net donor concentration <1014 cm−3) films subsequently implanted with Si, Ge, and Sn. Upon Ohmic contact formation to the implanted regions, sheet resistance values of 314, 926, and 1676 Ω/sq were measured at room temperature for the Si-, Ge-, and Sn-implanted samples, respectively. Room temperature Hall measurements resulted in sheet carrier concentrations and Hall mobilities of 2.13 × 1014 /93, 8.58 × 1013/78, and 5.87 × 1013/63 cm2/(V s), respectively, for these three donor species. Secondary ion mass spectroscopy showed a volumetric dopant concentration of approximately 2 × 1019 cm−3 for the three species, resulting in carrier activation efficiencies of 64.7%, 40.3%, and 28.2% for Si, Ge, and Sn, respectively. Temperature-dependent Hall effect measurements ranging from 15 to 300 K showed a nearly constant carrier concentration in the Si-implanted sample, suggesting the formation of an impurity band indicative of degenerate doping. With a bulk carrier concentration of 1.3 × 1019 cm−3 for the Si implanted sample, a room temperature mobility of 93 cm2/(V s) is among the highest reported in Ga2O3 with a similar carrier concentration. The unimplanted Ga2O3:N regions remained highly resistive after the surrounding areas received implant and activation anneal. These results open the pathway for fabricating Ga2O3 devices through the selective n-type doping in highly resistive epitaxial Ga2O3. [ABSTRACT FROM AUTHOR]

GaN and its alloys with InN and AlN are of technological importance for a variety of optical, electronic, and optoelectronic devices due to its high thermal conductivity, wide band gap, high breakdown voltage and high saturation velocity. GaN-based devices now provide superior performance for a variety of high power, high frequency, high temperature, and optical applications. The major roadblock for the full realization of Nitride semiconductor potential is still the availability of affordable large-area and high-quality native substrates with controlled electrical properties. Despite the impressive accomplishments recently achieved by techniques such as hydride vapor phase epitaxy and ammonothermal for GaN growth, much more must be attained before establishing a fully satisfactory bulk growth method for this material. Recent results suggest that ammonothermal GaN wafers can be successfully used as seeds to grow thick freestanding GaN wafers by hydride vapor phase epitaxy. A brief review of defect-sensitive optical and paramagnetic spectroscopy techniques employed to evaluate structural, optical, and electronic properties of the state-of-the-art bulk and thick-film (quasi-bulk) Nitride substrates and homoepitaxial films is presented. Defects control the performance of devices and feeding back knowledge of defects to growth efforts is key to advancing technology. [ABSTRACT FROM AUTHOR]

The ultra-wide bandgap semiconductor gallium oxide (Ga2O3) offers substantial promise to significantly advance power electronic devices as a result of its high breakdown electric field and maturing substrate technology. A key remaining challenge is the ability to grow electronic-grade epitaxial layers at rates consistent with 20–40 μm thick drift regions needed for 20 kV and above technologies. This work reports on extensive characterization of epitaxial layers grown in a novel metalorganic chemical vapor deposition tool that permits growth rates of 1.0–4.0 μm h−1. Specifically, optical, structural and electrical properties of epilayers grown at ∼1 μm h−1 are reported, including employment in an operating MOSFET. The films demonstrate relatively smooth surfaces with a high degree of structural order, limited point defectivity (Nd − Na ≈ 5 × 1015 cm−3) and an optical bandgap of 4.50 eV. Further, when employed in a MOSFET test structure with an n+ doped channel, a record high mobility for a transistor structure with a doped channel of 170 cm2 V−1 s−1 was measured via the Hall technique at room temperature. This work reports for the first time a β-Ga2O3 MOSFET grown using Agnitron Technology's high growth rate MOCVD homoepitaxial process. These results clearly establish a significant improvement in epilayer quality at growth rates that can support future high voltage power device technologies. [ABSTRACT FROM AUTHOR]

This paper presents the homoepitaxial growth of phase pure (010) β-Ga2O3 thin films on (010) β-Ga2O3 substrate by low pressure chemical vapor deposition. The effects of growth temperature on the surface morphology and crystal quality of the thin films were systematically investigated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O2) as precursors for gallium and oxygen, respectively. The surface morphology and structural properties of the thin films were characterized by atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. Material characterization indicates the growth temperature played an important role in controlling both surface morphology and crystal quality of the β-Ga2O3 thin films. The smallest root-mean-square surface roughness of ~7 nm was for thin films grown at a temperature of 950 °C, whereas the highest growth rate (~1.3 lm/h) with a fixed oxygen flow rate was obtained for the epitaxial layers grown at 850 °C. [ABSTRACT FROM AUTHOR]

Thick freestanding GaN substrates with low background free-carrier concentrations were subjected to 6MeV beam proton irradiations. The beam penetration depth, incident perpendicularly to the c-axis, and the change in the carrier concentrations were accessed by monitoring the phonon-plasmon coupled mode by micro-Raman spectroscopy. Reduction of the Raman shift of the A1(LO)-plasmon coupled mode confirmed that the free-carrier concentrations decreased after proton irradiations. The penetration depth of 6MeV protons was inferred from the point where phonon-plasmon coupled mode frequencies changed abruptly. The carrier concentrations in the GaN templates before irradiations were 4×1016 cm-3. However, after proton irradiation, the concentration decreased to less than 1×1015 cm-3 resulting from the incorporation of defects trapping free carriers. It was estimated from the lowest phonon frequencies that most of the irradiated protons stop near 180 μm, which was consistent with the results of Monte Carlo numerical simulations (SRIM). Most of the irradiation-induced lattice damage was recovered after 2 minutes of thermal annealing at 900 °C, as verified by the spectra of the A1(LO)-plasmon coupled mode. [ABSTRACT FROM AUTHOR]

A striking feature of the Hope Diamond is its long-lasting orange-red phosphorescence (see, e.g., figure 5 in Crowningshield, 1989). Other than visual and photographic observation, this luminescence has not been studied. Our experiments employed a technique not often used in gemology, phosphorescence spectroscopy, which was performed on 60 natural blue diamonds from the Aurora Butterfly and Aurora Heart collections, in addition to the Hope Diamond and the Blue Heart diamond. The data were collected using an Ocean Optics deuterium lamp, a fiber-optic assembly to transmit the light, and a USB 2000 spectrometer to record the phosphorescence spectra. Because of the risk of damaging these unique gems, we could not perform several scientifically desirable experiments (such as spectroscopy at liquid nitrogen temperatures). Most luminescence measurements were taken at room temperature, so the majority of the spectra showed broad peaks and no sharp lines. Nearly all spectra of the blue diamonds examined showed a combination of greenish blue (500 nm) and red (660 nm) phosphorescence. The intensities and the half-lives of each luminescence peak differed for each diamond, which would account for the variety of phosphorescence colors (blue to red) reported by previous researchers. The peak shapes were not significantly different between diamonds, and the peak maxima did not shift with time after the first second. Blue diamonds are typically type IIb and contain boron impurities. For comparison, we tested four blue HPHT-grown, type IIb synthetic diamonds. These stones exhibited a phosphorescence peak at 500 nm (and also at 575 nm in one diamond), but not at 660 nm. Prior research has demonstrated that donor-acceptor pair recombination is a likely cause of several bands observed by laser-induced photoluminescence and phosphorescence in synthetic diamonds (see, e.g., Watanabe et al., 1997). In this scenario, holes that are trapped on acceptors (such as boron) and electrons trapped on donors recombine and emit light equivalent to the difference in energy that they possess while separated. This is the first study of natural type lib diamonds that demonstrates a similar mechanism operating in natural stones. [ABSTRACT FROM AUTHOR]

Oxygen is a common substitutional impurity in both AlN and GaN crystals. In the wurtzite 2H phase it can be present in AlN up to concentrations of 1×1021/cm3 while in GaN it can reach concentrations of 3×1022/cm3. These high concentrations of oxygen affect the luminescence, the optical absorption, the thermal conductivity, and the crystal perfection. The effects are somewhat similar in AlN and GaN. Representative experimental data will be presented to demonstrate the similarities, and to show how the oxygen content may be estimated from these property measurements. [Copyright &y& Elsevier]