GaNAs films grown on GaAs͑001͒ substrates by metalorganic molecular beam epitaxy were studied by high-resolution x-ray diffraction ͑XRD͒ mapping measurements. The lattice constants of epitaxial films are usually estimated from symmetric and asymmetric XRD 2 Ϫ measurements. In this study, it is pointed out that the consideration of the tilt angle between the GaAs͑115͒ and GaNAs͑115͒ planes caused by elastic deformation of the films is crucial to determine the lattice constants of the GaNAs films coherently grown on GaAs substrates. Mapping measurements of ͑115͒ XRD (2 Ϫ )Ϫ⌬ were performed for this purpose. The band gap energy of the films was determined by Fourier transform absorption spectroscopy measurements. The band gap energy bowing measured up to the N composition of 4.5% will be discussed by comparing with other measurements and theoretical calculations.
We have observed a significant reduction in the temperature dependence of the absorption-edge energy in GaNxAs1−x alloys with x<0.04. The effect has been analyzed in terms of the recently introduced band anticrossing model that considers a coupling of the temperature-independent localized states of substitutional nitrogen atoms and the temperature-dependent extended states of GaAs. The model explains very well the alloy composition and the temperature dependence of the absorption-edge energy. We also compare the parameters that determine the temperature dependence of the band-gap energies in GaNAs and GaInNAs alloys.
The temperature dependence of band gap energies of GaAsN alloys was studied with absorption measurements. As the N concentration in GaAsN increased, the temperature dependence of the band gap energy was clearly reduced in comparison with that of GaAs. The redshift of the absorption edge in GaAsN for the temperature increase from 25 to 297 K was reduced to 60% of that of GaAs for the N concentration larger than ϳ1%. The differential temperature coefficient of the energy gap at room temperature was also reduced to 70% of that of GaAs. The main factor for this reduced temperature dependence in GaAsN was attributed to the transition from band-like states to nitrogen-related localized states with detailed studies of the temperature-induced shift of the absorption edge. © 2000 American Institute of Physics. ͓S0003-6951͑00͒04110-3͔ III-V-N alloys such as GaAsN and GaInNAs have been intensively studied to realize long-wavelength semiconductor lasers with higher temperature stability for optical-fiber communications.1 Although 1.3 m semiconductor lasers based on the InGaAsP/InP system have been commonly used, their lasing threshold currents are highly temperature dependent due to poor carrier confinements in InGaAsP quantum wells. GaInNAs/AlGaAs system grown on GaAs substrates will be able to confine electrons more tightly in the quantum wells due to the larger conduction bands offsets compared with the InGaAsP system, which will efficiently prevent leakage currents and will reduce the temperature dependence of the threshold currents.1 The higher temperature stability of the lasing threshold was demonstrated in a GaInNAs laser operating at around 1.3 m. 2In addition to the stability of the lasing threshold against the environment change, the stability of the lasing wavelength is another important requirement on laser light sources for optical-fiber communications. Perlin et al.3 recently studied the pressure and temperature dependence of the absorption edge of a Ga 0.92 In 0.08 N 0.015 As 0.985 alloy. They reported that the hydrostatic pressure coefficient of the band gap of the GaInNAs was more than a factor of 2 lower than that of GaAs. The temperature-induced shift of the absorption edge of GaInNAs was 12% smaller than that of GaAs. They explained this phenomenon by the large decrease of the deformation potential.In this letter, the relation between the temperature dependence of the band gap energy of the GaAsN alloys and their N concentration is studied. A substantial decrease of the temperature dependence was found in GaAsN, and the transition from the temperature dependence of GaAs band-like states to that of more localized states was observed for the higher N concentrations.0.1-6.2-m-thick GaAsN films were grown on semiinsulating GaAs͑001͒ substrates by metalorganic molecularbeam epitaxy. The metalorganic precursors used were triethylgallium, monomethylhydrazine, and trisdimethylaminoarsenic ͑TDMAAs͒. After thermal cleaning of GaAs substrate surfaces at 600°C with the simultaneous supply of TDMAAs, GaAsN layers we...
Realization of solid-state photon sources which are capable of on-demand generation of entangled single photon pair at a time is highly desired for quantum information processing and communication. A new method to generate entangled single photon pair at a time is proposed employing Cooper-pair-related radiative recombination in a quantum dot (QD).Cooper pairs are bosons and the control of their number states is not easy. The Pauli's exclusion principle on quasi-particles in a discrete state of a QD will regulate the number state of the generated photon pairs in this scheme. The fundamental heterostructures for constructing superconductor-based quantum-dot light-emitting diodes (SQ-LED) and the fundamental operation conditions of SQ-LED will be discussed. The experimental studies on Cooper-pair injection into the related semiconductor structures will be also discussed.
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