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We present data on mobility lifetime τ[sub t], quantum lifetime τ[sub q], and cyclotron resonance lifetime τ[sub CR], of a sequence of high-mobility two-dimensional electron gases in the AlGaN/GaN system, covering a density range of 1 to 4.5×10[sup 12] cm[sup -2]. We observe a large discrepancy between τ[sub q] and τ[sub CR](τ[sub q]∼τ[sub CR]/6), and explain it as the result of density fluctuations of only a few percent. Therefore, only τ[sub CR]—and not τ[sub q]—is a reliable measure of the time between electron-scattering events in these specimens. The ratio τ[sub t]/τ[sub CR] increases with increasing density in this series of samples, but scattering over this density range remains predominantly in the large-angle scattering regime. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Describes a technique based on photoelectrochemical wet etching that enables efficient and accurate evaluation of dislocation densities in n-type GaN thin films. Use of dilute aqueous KOH solutions and Hg arc lamp illumination by the etching process to produce GaN whiskers.

Examines the gallium nitride/sapphire interface using temperature-dependent Hall-effect measurements. Impact of the degenerate interfacial region on electrical properties; Role of the region in the false appearance of a second donor; Determination of the bulk mobility and carrier concentration of the interface using a two layer Hall model.

Reports the growth of blue-violet gallium nitride light emitting p-n junctions by the method of electron cyclotron resonance-assisted molecular beam epitaxy. Reports on the fabrication of p-n junction light emitting diodes; Use of electron cyclotron resonance-plasma activated nitrogen gas; Observation of magnesium luminescence characteristics.

Examines the intensity dependence of photoluminescence in gallium nitride films. Use of electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy; Identification of linear and nonlinear luminescence dependency on light intensity; Difference in recombination center voltage density between data and recombination model.

Examines electron transport mechanism in gallium nitride. Analysis of the temperature dependence of Hall coefficient and resistivity on samples; Determination of the activation energy; Decrease of the concentration of the autodoping centers.

Examines the epitaxial growth of zinc blende and wurtzitic gallium nitride thin films on (001) silicon by electron cyclotron resonance microwave plasma-assisted molecular beam epitaxy. Components of the deposition system; Discussion on the film two-step growth process; Influence of the buffer layer on the film growth.

Using several scanning probe techniques to investigate local electronic properties, we show that the GaN/sapphire interfacial region contains >= ten times higher electron density but with the Fermi level being 50-100 meV deeper in the band gap compared to the less-conducting bulk film. This anomalous behavior cannot be explained by transport in the intrinsic conduction band of GaN. Rather, it points to the existence of a partially filled donor impurity band. We relate the presence of this impurity band conduction to excess oxygen in the region and the defective microstructure at the GaN/sapphire interface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report on the growth and transport properties of high-mobility two-dimensional electron gases (2DEGs) confined at the AlGaN/GaN interface grown by plasma-assisted molecular-beam epitaxy on GaN templates prepared by hydride vapor phase epitaxy. We have grown samples over a broad range of electron densities ranging from n[sub s]=6.9x10[sup 11] to 1.1x10[sup 13] cm[sup -2], and at T=4.2 K, observe a peak mobility of 53 300 cm[sup 2]/V s at a density of 2.8x10[sup 12] cm[sup -2]. Magnetotransport studies on these samples display exceptionally clean signatures of the quantum Hall effect. Our investigation of the dependence of 2DEG mobility on carrier concentration suggests that the low-temperature mobility in our AlGaN/GaN heterostructures is currently limited by the interplay between charged dislocation scattering and interface roughness. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron beam and optical depth profiling of thick (5.5-64 μm) quasibulk n-type GaN samples, grown by hydride vapor-phase epitaxy, were carried out using electron beam induced current (EBIC), microphotoluminescence (PL), and transmission electron microscopy (TEM). The minority carrier diffusion length, L, was found to increase linearly from 0.25 μm, at a distance of about 5 μm from the GaN/sapphire interface, to 0.63 μm at the GaN surface, for a 36-μm-thick sample. The increase in L was accompanied by a corresponding increase in PL band-to-band radiative transition intensity as a function of distance from the GaN/sapphire interface. We attribute the latter changes in PL intensity and minority carrier diffusion length to a reduced carrier mobility and lifetime at the interface, due to scattering at threading dislocations. The results of EBIC and PL measurements are in good agreement with the values for dislocation density obtained using TEM. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Photon counting, utilizing Geiger-mode avalanche response, has been demonstrated at 300 K in avalanche photodiodes fabricated in GaN grown by hydride vapor-phase epitaxy. Measurements have been made using both passive-quench and time-gated modes of operation. The two important figures of merit for photon-counting applications, photon detection efficiency (PDE) and dark count rate, were measured. A maximum PDE of 13% was measured at 325 nm with a dark count rate of 400 kHz. Typical mesa-etched devices exhibit a parasitic shunt leakage current of less than 20 nA at 90% of breakdown voltage. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]