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We report on ultrahigh resolution studies of the bound exciton states associated with the shallow acceptor B and the shallow donor P in highly enriched 28Si using a tuneable single frequency laser to perform photoluminescence excitation spectroscopy. The linewidths and fine structure of the transitions, which were too narrow to be resolved previously using an available photoluminescence apparatus, are now fully revealed. The P bound exciton transition shows a complicated additional structure, which the Zeeman spectroscopy demonstrates to be a result of the splitting of the donor ground state by the hyperfine interaction between the spin of the donor electron and that of the 31P nucleus. The 31P nuclear spin populations can thus be determined, and hopefully modified, by optical means. The predominant Auger recombination channel of these bound excitons is used to observe the same resolved hyperfine transitions in the photocurrent spectrum. This demonstrates that donors in specific electronic and nuclear spin configurations can be selectively photoionized. Possible applications of these results to quantum computing and quantum information systems are discussed. [ABSTRACT FROM AUTHOR]

The photoluminescence (PL) of Er-doped silica films containing Ge nanoclusters synthesized by ion implantation was investigated. The area of the 1540 nm Er3+ PL peak was enhanced by up to a factor of 200 by the addition of Ge nanoclusters. The PL enhancement was found to be proportional to the concentration of Ge atoms. Control experiments with argon ion implantation were used to show that the enhancement is due to the presence of Ge and not radiation damage. Furthermore, the Er3+ PL was found to be strongly influenced by the postgrowth annealing and the crystallinity of the Ge nanoclusters. [ABSTRACT FROM AUTHOR]

Irradiation of InN films with 2 MeV He+ ions followed by thermal annealing below 500 °C creates films with high electron concentrations and mobilities, as well as strong photoluminescence. Calculations show that electron mobility in irradiated samples is limited by triply charged donor defects. Subsequent thermal annealing removes a fraction of the defects, decreasing the electron concentration. There is a large increase in electron mobility upon annealing; the mobilities approach those of the as-grown films, which have 10 to 100 times smaller electron concentrations. Spatial ordering of the triply charged defects is suggested to cause the unusual increase in electron mobility. [ABSTRACT FROM AUTHOR]

The temperature dependence of the photoluminescence (PL) transitions associated with various excitons and their phonon replicas in high-purity bulk ZnO has been studied at temperatures from 12 K to above room temperature (320 K). Several strong PL emission lines associated with longitudinal optical (LO) phonon replicas of free and bound excitons are clearly observed. The room-temperature PL spectrum is dominated by the phonon replicas of the free exciton transition with the maximum at the first LO phonon replica. The results explain the discrepancy between the transition energy of free exciton determined by reflection measurement and the peak position obtained by the PL measurement. [ABSTRACT FROM AUTHOR]

The pressure dependence of the photoluminescence (PL) transition associated with the fundamental bandgap of ZnO nanowires has been studied at pressures up to 15 GPa. The near-bandedge luminescence emission is found to shift toward higher energy with applied pressure at a rate of 29.2 meV/GPa with a small second-order term of -0.38 meV/GPa2. An effective hydrostatic deformation potential -3.92±0.15 eV for the direct bandgap of the ZnO nanowires is derived from the results. The broad green emission band in ZnO depends on pressure with a linear slope of 15.9 meV/GPa and a quadratic coefficient of -0.71 meV/GPa2. The results indicate that the initial states involved in the emission process are deep localized states. [ABSTRACT FROM AUTHOR]

The effect of alloying small amounts of ZnO with ZnSe on the electronic band structure has been studied. Optical transitions in molecular-beam-epitaxy-grown ZnO[SUBx]Se[SUB1-x] epitaxial films (0⩽x ⩽1.35%) were investigated using photoreflectance and photoluminescence spectroscopies. The fundamental band-gap energy of the alloys was found to decrease at a rate of about 0.1 eV per atomic percent of oxygen. The pressure dependence of the band gap was also found to be strongly affected by O incorporation. Both the effects can be quantitatively explained by an anticrossing interaction between the extended states of the conduction band of ZnSe and the highly localized oxygen states located at approximately 0.22 eV above the conduction-band edge. [ABSTRACT FROM AUTHOR]

The optical properties of wurtzite-structured InN grown on sapphire substrates by molecular-beam epitaxy have been characterized by optical absorption, photoluminescence, and photomodulated reflectance techniques. These three characterization techniques show an energy gap for InN between 0.7 and 0.8 eV, much lower than the commonly accepted value of 1.9 eV. The photoluminescence peak energy is found to be sensitive to the free-electron concentration of the sample. The peak energy exhibits very weak hydrostatic pressure dependence, and a small, anomalous blueshift with increasing temperature. [ABSTRACT FROM AUTHOR]

We present results of pressure-dependent photoluminescence (PL) studies of single-crystal Al[sub x]Ga[sub 1-x]N epitaxial films grown on sapphire substrates by metalorganic chemical vapor deposition. PL measurements were performed under hydrostatic pressure using the diamond-anvil-cell technique. PL spectra taken from the Al[sub x]Ga[sub 1-x]N epitaxial films are dominated by strong near-band-edge luminescence emissions. The emission lines were found to shift linearly towards higher energy with increasing pressure. By examining the pressure dependence of the spectral features, the pressure coefficients for the PL emissions associated with the direct Γ band gap of Al[sub x]Ga[sub 1-x]N were determined. Our results yield a pressure coefficient of 4.0×10[sup -3] eV/kbar for Al[sub 0.05]Ga[sub 0.95]N and 3.6×10[sup -3] eV/kbar for Al[sub 0.35]Ga[sub 0.65]N. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the results of a comparison study of photoluminescence (PL) from an In[sub 0.15]Ga[sub 0.85]N/GaN multiple-quantum-well (MQW) sample and an In[sub 0.11]Ga[sub 0.89]N thick epitaxial-layer sample, which have very similar band-gap energies. Large hydrostatic pressures were used for our investigations. The PL emissions in both samples were found to shift linearly to higher energy with applied pressure. In the MQW sample, the pressure response of the InGaN is dominated by the GaN layers, which leads to a significantly weaker pressure dependence as compared to the epilayer sample. Our results yield a pressure coefficient of 2.8×10[sup -3] eV/kbar for the In[sub 0.15]Ga[sub 0.85]N/GaN MQW sample and 4.0×10[sup -3] eV/kbar for the In[sub 0.11]Ga[sub 0.89]N epilayer. An abrupt decrease of PL intensity in both samples was observed at pressures above 100 kbar, indicating the carriers involved in the radiative recombination processes in the samples originate primarily from the adjacent GaN layers. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]