The near band edge photoluminescence (PL) of cubic GaN epilayers grown by radio frequency (rf) plasma-assisted molecular beam epitaxy on (100) GaAs is measured. Since the PL is excited with an unfocused laser beam it resembles the layer properties rather than the properties of micron-size inclusions or micro crystals. The low temperature PL spectra show well separated lines at 3.26 and 3.15 eV which are due to excitonic and donor-acceptor pair transitions (donor binding energy 25 meV, acceptor binding energy 130 meV). No emission above the band gap of the cubic phase is detected. PL results are confirmed by x-ray diffraction and atomic force microscopy which reveal only negligible contributions from hexagonal inclusions and micron size single crystals. The room temperature PL consists of an emission band at about 3.21 eV with a full width at half maximum of 117 meV.

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Near infrared spectroscopy (NIRS) has been successfully used in this study to objectify cerebral alterations in oxyhemoglobin and desoxyhemoglobin, due to manual needle acupuncture and laserneedle acupuncture, in 88 healthy volunteers mean age 25.7±4.0 (x¯±SD) years (19–38 years). Results from Traditional Chinese Acupuncture, Korean and Chinese hand acupuncture, ear acupuncture, combinations of the different acupuncture methods and placebo needling are presented. NIRS seems to be able to shed some light upon the functioning of the different acupuncture methods.

High-quality ZnS, ZnSe, and ZnTe epitaxial films were grown on ͑001͒-GaAs-substrates by molecular beam epitaxy. The 1s-exciton peak energy positions have been determined by absorption measurements from 2 K up to about room temperature. For ZnS and ZnSe additional high-temperature 1s-exciton energy data were obtained by reflectance measurements performed from 300 up to about 550 K. These complete E 1s (T) data sets are fitted using a recently developed analytical model. The high-temperature slopes of the individual E 1s (T) curves and the effective phonon temperatures of ZnS, ZnSe, and ZnTe are found to scale almost linearly with the corresponding zero-temperature energy gaps and the Debye temperatures, respectively. Various ad hoc formulas of Varshni type, which have been invoked in recent articles for numerical simulations of restricted E 1s (T) data sets for cubic ZnS, are discussed.

Phase separation suppression due to external biaxial strain is observed in InxGa1−xN alloy layers by Raman scattering spectroscopy. The effect is taking place in thin epitaxial layers pseudomorphically grown by molecular-beam epitaxy on unstrained GaN(001) buffers. Ab initio calculations carried out for the alloy free energy predict and Raman measurements confirm that biaxial strain suppress the formation of phase-separated In-rich quantum dots in the InxGa1−xN layers. Since quantum dots are effective radiative recombination centers in InGaN, we conclude that strain quenches an important channel of light emission in optoelectronic devices based on pseudobinary group-III nitride semiconductors.

The emission of light in the blue-green region from cubic InxGa1-xN alloys grown by molecular beam epitaxy is observed at room temperature and 30 K. By using selective resonant Raman spectroscopy (RRS) we demonstrate that the emission is due to quantum confinement effects taking place in phase-separated In-rich quantum dots formed in the layers. RRS data show that the In content of the dots fluctuates across the volume of the layers. We find that dot size and alloy fluctuation determine the emission wavelengths.

We have investigated the growth kinetics of the self-assembled formation of coherently strained CdSe islands. We have found that two distinctly different types of islands are formed in succession. Analyzing the density distribution function of the two dominating size classes of islands, we show that islands of an average diameter of about 16 nm (type B islands) are correlated with a phase transition via a Stranski–Krastanow growth process. The other islands with a diameter of less than 10 nm (type A islands) is formed during the growth of the first 2 ML. At a coverage of about 3.1 ML CdSe stacking faults appear, indicating the beginning of the plastic relaxation of the quantum dot structure.

Hexagonal and cubic GaN layers are grown on (001) GaAs substrates by means of molecular beam epitaxy. First order Raman spectra are taken from these layers at various incident laser wavelengths and temperatures. The T2 transverse-optical (TO) and longitudinal-optical (LO) frequencies of cubic GaN are determined, as well as the A1 TO and LO, E1 TO, and E2 frequencies of hexagonal GaN. The T2 TO frequency of cubic GaN lies between the A1 and E1 TO frequencies of hexagonal GaN as one expects comparing the lattice dynamics of zincblende and wurtzite type crystals. The T2 TO frequency is close to the calculated value but disagrees with a recently reported experimental value. For the hexagonal layer, all frequencies are close to those previously measured. A broad Raman structure below the A1 LO peak is interpreted in terms of a disturbed long range order of the hexagonal layer.