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p-Type GaN is an important semiconducter material for optical and electronic devices. The samples did not show any electrical activities using Hall measurements, when the origins of leaky characteristics of Scottky barrier of pGaN grown by MOCVD are investigated.

A new study uses modulation spectroscopy and photoluminescence to investigate the compositional dependence of the optical properties of AlxGa1-xN/GaN alloys.

Research is presented concerning the use of photoluminescence spectroscopy to investigate the optical transitions in multiple quantum well microdisks of In0.22Ga0.78N/In0.06Ga0.94N which have a diameter of 6.0-micrometers.

The formation mechanism of the ohmic Au/Ni/p-GaN contact was studied.

The Schottky barrier height dependence of Ni/AIxGa1-xN on the A1 mole fraction was examined.

Research was conducted to determine the Al mole fraction in both bulk AlGaN adn AlGaN/GaN heterostructure samples using the photoconductance method. Samples were grown by metalorganic vapor phase epitaxy. Results were in agreement with those derived by a much more elaborate photoluminescence measurement. Results show that the photodonductance approach is a simple and convenient way to calculate the Al mole fraction in AlGAN.

The persistent photoconductivity effect linked to a two-dimensional electron gas (2DEG) in an AlGaN/GaN heterojunction device has been established. Permanent photoinduced increase in 2DEG carrier mobility and density has a causal relationship with the device. Photoexcited carrier density and 2DEG carrier mobility have a positive linear correlation. Device applications using AlGaN/GaN heterojunctions are covered.

We study thermal annealing effects on the size and composition variations of indium-aggregated clusters in two InGaN thin films with photoluminescence (PL) in the yellow and red ranges. The methods of investigation include optical measurement, nanoscale material analysis, and theoretical calculation. Such a study is important for determining the relation between the band gap and the average indium content of InGaN. In one of the samples, the major part of the PL spectrum is shifted from the yellow band into the blue range upon thermal annealing. In the other sample, after thermal annealing, a broad spectrum covering the whole visible range is observed. To obtain a basic physics picture behind the spectral blue shift upon thermal annealing in the yellow emission sample, we theoretically study the quantum-confinement effects of InGaN clusters based on a quantum box model. [ABSTRACT FROM AUTHOR]

n- and p-type Al[sub x]Ga[sub 1-x]N (x=0.38 for n-type, x=0.13 for p-type) layers grown on Al[sub 2]O[sub 3] substrates were ion implanted with the transition metals Mn, Cr, and Co at high concentrations (peak doping levels ∼3 at. %). After implantation and annealing at 1000 °C, only impurity transitions at ∼2.9 and 3.9 eV and no band-edge photoluminescence could be observed in all the samples. X-ray diffraction did not detect any peaks associated with second phase formation. Room-temperature hysteresis loops were obtained for Co-implanted n-type AlGaN, while there was no convincing evidence for ferromagnetism in the Mn- or Cr-implanted n-AlGaN. By sharp contrast, Mn implantation in p-AlGaN did produce ferromagnetic behavior and 300 K hysteresis. Both carrier type and crystalline quality can influence the resulting magnetic properties. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

[Cd.sub.1-x][Mn.sub.x]S diluted magnetic semiconductor (DMS) nanoparticles of crystallite size ranging from 20 to 300 [Angstrom] and x from 0 to 0.65 have been chemically synthesized by using aqueous solution precipitation. Subsequent characterization has been carried out by X-ray diffractometry and TEM measurements. Magnetic properties of DMS nanoparticles have been measured with a SQUID magnetometer: A transition from a para-magnetic to a spin-glass state at a critical temperature [T.sub.f] has been observed. The applied magnetic field dependence of [T.sub.f] has also been measured.

Light illumination techniques reveal the thermoremanent magnetization relaxation in diluted magnetic semiconductors Cd(1-x)Mn(x)Te in the spin-glass state. The power law decay explains the relaxation, with changes in the decay parameter alpha due to the light intensity resulting in the proportionality of alpha to photogenerated carrier concentration.

The indium aggregation phenomena in two InGaN thin films with (photoluminesence) PL in the Yellow and red ranges and their variations upon post-growth thermal annealing through optical measurement, material analysis and theoretical calculations is described. The theoretical approach to quantum -confinement effect of InGaN clusters based on a quantum box model is presented.