Negative differential resistance associated with hot phonons J. Appl. Phys. 112, 063707 (2012) Photoluminescence properties and high resolution x-ray diffraction investigation of BInGaAs/GaAs grown by the metalorganic vapour phase epitaxy method J. Appl. Phys. 112, 063109 (2012) Optical properties of InGaPN epilayer with low nitrogen content grown by molecular beam epitaxy J. Appl. Phys. 112, 063507 (2012) Residual compressive stress induced infrared-absorption frequency shift of hexagonal boron nitride in cubic boron nitride films prepared by plasma-enhanced chemical vapor deposition J. Appl. Phys. 112, 053502 (2012) Spontaneous emission and optical gain characteristics of blue InGaAlN/InGaN quantum well structures with reduced internal fieldWe present the results of optical studies of the properties of In x Ga 1Ϫx N epitaxial layers (0Ͻx Ͻ0.2) grown by metalorganic chemical vapor deposition. The effects of alloying on the fundamental band gap of In x Ga 1Ϫx N were investigated using a variety of spectroscopic techniques. The fundamental band-gap energies of the In x Ga 1Ϫx N alloys were determined using photomodulation spectroscopy measurements and the variation of the fundamental band gap was measured as a function of temperature. The effects of pressure on the band gap for In x Ga 1Ϫx N samples with different alloy concentrations were examined by studying the shift of photoluminescence ͑PL͒ emission lines using the diamond-anvil pressure-cell technique. The results show that PL originates from effective-mass conduction-band states. Anomalous temperature dependence of the PL peak shift and linewidth as well as the Stokes shift between photoreflectance and PL lines is explained by composition fluctuations in as-grown InGaN alloys.

No abstract

We present the results of optical studies of InxGa1−xN alloys (0<x<0.2) grown by metalorganic chemical vapor deposition on top of thick GaN epitaxial layers with sapphire as substrates. Photoluminescence (PL) and photoreflectance measurements were performed at various temperatures to determine the band gap and its variation as a function of temperature for samples with different indium concentrations. Carrier recombination dynamics in the alloy samples were studied using time-resolved luminescence spectroscopy. While the measured decay time for the alloy near-band-edge PL emissions was observed to be generally around a few hundred picoseconds at 10 K, it was found that the decay time decreased rapidly as the sample temperatures increased. This indicates a strong influence of temperature on the processes of trapping and recombination of excited carriers at impurities and defects in the InGaN alloys.

The second-order nonlinear optical coefficients d33, d31, and d15 of GaN:Mg epitaxial film were studied by the standard Maker fringe of an anisotropic medium. The measured d33=−(16.5±1.3) pm/V which is 55 times of the d11 of quartz. The measured ratios of d33/d31 and d31/d15 showed that the crystalline film is close to an ideal wurzite structure. The refractive indices and the dispersive curves of ne, n0 were also determined by TM and TE waveguide mode measurements.

We have studied the effect that structural defects and chemical impurities have on the electron mobility in GaN films grown in a production scale metalorganic chemical vapor depositon system. Structural defects such as dislocations, stacking faults, twins, and amorphous regions in the buffer layer have been examined. In general, we have found that the structural defects are not the primary contributor to low mobility. However, there is one type of defect Cnanopipe") that may be an important indirect contributor to mobility degradation by acting as a conduit into the film interior for impurities such as carbon and oxygen. We have also investigated the role that the principal impurities play in determining the electrical performance. Of particular concern was the presence of carbon resulting from an incomplete dissociation of trimethylgallium precursor gas. Also present in the films were traces of oxygen, hydrogen, and aluminum, while heavy metals such as iron, chromium, and molybdenum were detected at or near the resolution limit of secondary ion mass spectrometry analysis. We present evidence for compensation by carbon at low carrier concentrations, which would help to explain the anomalous mobility behavior in GaN.