Optical Properties of GaNAs Grown by MBE
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Internet Journal Nitride Semiconductor Research
Optical Properties of GaNAs Grown by MBE G. Pozina1, I. G. Ivanov1, B. Monemar1, J.V. Thordson23 and T.G. Andersson23 1Department
of Physics and Measurement Technology, Linköping University, University of Technology, 3University of Göteborg, Sweden, 2Chalmers
(Received Tuesday, April 7, 1998; accepted Monday, September 28, 1998)
Optical properties of the GaNxAs1-x layers grown on (001) GaAs substrates by molecular beam epitaxy have been studied. The samples can be classified into three categories with respect to the concentration of N, as determined by x-ray diffraction and secondary-ion mass spectrometry: (i) with doping nitrogen concentration, (ii) with average content of N less than 30 %, and (iii) with x close to 100 %. From optical measurements of photoluminescence and Raman scattering, combined with analysis of x-ray diffraction spectra, different phases are observed in the GaNxAs1-x layers: GaAs, GaN and the solid ternary solution GaNxAs1-x. We have estimated the fundamental band-gap energy in the GaNxAs1-x alloy with low nitrogen concentration (up to x = 0.04) from absorption measurements, and in GaNxAs1-x with low arsenic concentration (up to 1-x = 0.04) - from photoluminescence spectra. An analysis of the dependence of the experimental values of the GaNxAs1-x band-gap energy on the nitrogen composition indicates a constant bowing parameter b as large as b = -18 eV.
1
Introduction
Studies of mixed group-V alloys like GaNAs are currently of great fundamental interest, and they may also offer application possibilities for optoelectronic devices. The large difference in lattice constant (20%) between GaAs and GaN leads to a nonlinear behavior of the energy gap versus nitrogen concentration. Recent optical measurements show a considerable red shift of the band edge in GaNxAs1-x alloys with increasing x for low x values [1] [2] [3]. This property may be used for applications of GaNxAs1-x as a novel III-V compound material integrated with Si [4]. Growth of GaNxAs1-x with a nitrogen concentration varying in the broad range 0 < x < 1 can give a promising semiconductor alloy for fabrication of light-emitting devices covering the whole visible and ir spectrum. Theoretical predictions of the GaNxAs1-x electronic structure depend strongly on the model used and show contradictory results. Sakai et al. [5], using Van Vechten's model [6], and Neugebauer and Van de Walle [7], using first-principles total energy calculations, predicted a negative band gap for N concentrations in the range 0.09 - 0.87 and 0.16 - 0.71, respectively. In contrast, calculations of Bellaiche et al. [8], based on a
supercell representation of the alloy, confirmed the previous suggestion of Wei and Zunger [9] that GaNxAs1-x is a semiconductor rather than a semimetal for the whole range of x, and that the optical bowing parameter is strongly composition dependent, unlike the case of conventional III-V alloys. The band gap energy estimated from photoluminescence and absorption measurements foll
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