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InGaN epitaxial films grown by metalorganic chemical vapor deposition using trimethylgallium and triethylgallium as precursors exhibited different optical and electrical properties. The films were characterized by x-ray diffraction, photoluminescence, secondary ion mass spectroscopy, and atomic force microscopy. Impacts of unactivated Mg-doped GaN in situ grown cap layers on InGaN and GaN films were further investigated. Current-voltage and spectral response measurements combined with Hall-effect measurement and analytical modeling have been used to assess possible current transport mechanisms of reverse dark and photo current flow in metal-semiconductor-metal photodetectors fabricated from InGaN and GaN. Unlike the dominant thermionic emission, which can be blocked by higher and thicker potential barrier in GaN, the trap-assisted tunneling is more pronounced in InGaN. The passivation effect on high density surface states in InGaN is proposed to explain the improved device performances after the incorporation of Mg-doped GaN. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) ultraviolet metal-semiconductor-metal photodetectors (PDs) grown on Si substrates were demonstrated. The dark current of PDs fabricated on Si substrates was substantially smaller in magnitude compared to identical devices prepared on sapphire substrates. With an incident wavelength of 359 nm, the maximum responsivities of the n--GaN MSM photodetectors with TiW and Ni/Au contact electrodes were 0.187 and 0.0792 A/W, corresponding to quantum efficiencies of 64.7% and 27.4%, respectively. For a given bandwidth of 1 kHz and a given bias of 5 V, the corresponding noise equivalent powers of our n--GaN MSM photodetectors with TiW and Ni/Au electrodes were 1.525×10-12 and 5.119×10-12 W, respectively. Consequently, the values of detectivity (D*) determined for devices with TiW and Ni/Au electrodes were then calculated to be 1.313×1012 and 3.914×1011 cm Hz0.5 W-1, respectively. [ABSTRACT FROM AUTHOR]

A two-step treatment by argon (Ar) and hydrogen plasma beam scanning was developed to modify the surface bonds of a hydrogenated amorphous carbon (a-C:H) film on indium tin oxide glass. The modified a-C:H film is an excellent layer for liquid crystal alignment, on which the pretilt angle of a nematic liquid crystal (ZLI-2293) can be adjusted by the two-step scanning treatment. The chemical bonding characteristics of the as-scanned a-C:H films were measured using micro-Raman and x-ray photoemission spectroscopies. The antiparallel cells were filled with the nematic liquid crystal on the as-scanned a-C:H film to measure the pretilt angle. Experimental results indicate that the carbon dangling bonds are generated through a bond-breaking process during the Ar plasma beam scanning step (first step). The hydrogen plasma beam scanning step (second step) can passivate some of the carbon dangling bonds that are generated in the first step. The pretilt angle decreases as the hydrogen plasma beam scanning time increases. The decrease of pretilt angle is due to the formation of C–H bonds that passivate the a-C:H film and limit the formation of C–O bonds in air. [ABSTRACT FROM AUTHOR]

The nitrogen coimplantation characteristics in the Mg- and Be-implanted GaN with different dopant concentration ratios have been systematically investigated. The Hall-effect measurements show that the p-type characteristics are produced in the Mg- and Be-implanted GaN by the coimplantation of N atoms and subsequent annealing, which is essentially related to the column II/V dopant concentration ratio and annealing condition. This behavior may be attributed to the reduction of self-compensation induced by N vacancies and the enhanced acceptor substitution, which is in reasonable agreement with the surface stoichiometric switching determined by x-ray photoelectron spectroscopy measurements. From photoluminescence data, the activation energy of the Be acceptor level is evaluated to be about 145 meV, which is shallower than that of the Mg acceptor. These experimental results indicate that the selective-area N coimplantation with Mg and Be atoms into GaN is an effective method to enhance the p-type conductivity and to improve the p-type Ohmic contact resistance. [ABSTRACT FROM AUTHOR]

By using organometallic vapor phase epitaxy we have prepared i-GaN/low temperature (LT) GaN/ Ni/Au (sample A) and i-GaN/Ni/Au (sample B) Schottky barrier ultraviolet (UV) photodiodes (PDs). It was found that we could significantly reduce leakage current and achieve a much larger photocurrent to dark current contrast ratio by introducing a LT GaN on top of the conventional nitride-based UV PDs. With an incident light wavelength of 350 nm and a - 1 V reverse bias, it was found that the measured responsivity was around 0.1 and 0.37 A/W for samples A and B, respectively. Furthermore, it was found that the operation speed of sample A is slower than that of sample B due to the highly resistive LT GaN layer induced large R C time constant. [ABSTRACT FROM AUTHOR]

[sup 28]Si[sup +] implantation into Mg-doped GaN, followed by thermal annealing in N[sub 2] was performed to achieve n[sup +]-GaN layers. Multiple implantation was used to form a uniform Si implanted region. It was found that the carrier concentration of the films changed from 3×10[sup 17] cm[sup -3] (p-type) to 5×10[sup 19] cm[sup -3] (n-type) when the samples were annealed in N[sub 2] ambient at 1000 °C. The activation efficiency of Si in Mg-doped GaN was as high as 27%. In addition, planar GaN n[sup +]–p junctions formed by Si-implanted GaN:Mg were also achieved. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Examines the elastic field of a semi-infinite wedge crack and its interaction with a screw dislocation under mode III loading conditions. Expression of the stress field around the wedge crack; Relationship between the stress intensity factors for the wedge and sharp cracks; Calculation of the crack extension force for the wedge crack.

Presents a study on the contactless electroreflectance of strained Zn0.79Cd0.21Se/ZnSe double quantum wells, grown by molecular beam epitaxy on GaAs substrates. Details on the intersub-band transitions in the CER spectra; Discussion on the quantum wells at 15 and 300 k; Comparison of the experimental and theoretical values for the transitions.

Presents a study which investigated the structural characteristics of Si[subm]GE[subn] strained layer superlattice (SLS) structures grown by molecular beam epitaxy. Effects of buffer layer composition on SLS; Description of the SLS structure; Properties of the structures.

Provides information on a study that investigated the shallow defect evolution in silicon-implanted and -annealed liquid-encapsulated Czochralski-grown gallium arsenide by photoluminescence experiments. Description of the three major emission lines found; Effects of the three shallow centers on silicon activation efficiency; Use of photoluminescence.

Studies the fabrication of neodymium-doped semiconductor light-emitting diodes (LED) by implanting ions into gallium arsenide epi-layer (EL). Details on the experiment; Information on the typical EL spectrum of GaAs:Nd LED; Reason for the low external quantum efficiency for the GaAs:Nd LED.

Focuses on a study which analyzed the strain distribution of a Ge[subx]Si[1-x] strained layer superlattice (SLS) as a function of the distance from the superlattice/substrate interface by Raman spectroscopy. Factor responsible for some potentially useful photonic and electronic applications; Case in which the upper layers of the superlattice could be used for subsequent device fabrication; Effectiveness of the Raman scattering technique.