Composition and carrier-concentration dependence of the electronic structure of InyGa1−yAs1−xNx films with nitrogen mole fraction of less than 0.012
The electronic structure of Si-doped InyGa1−yAs1−xNx films on GaAs substrates, grown by nitrogen-plasma-assisted molecular-beam epitaxy, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 and 300K. The films were approximately 0.5μm thick and had nitrogen mole fraction bet...
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Veröffentlicht in: | Journal of applied physics 2005-11, Vol.98 (9) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | The electronic structure of Si-doped InyGa1−yAs1−xNx films on GaAs substrates, grown by nitrogen-plasma-assisted molecular-beam epitaxy, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 and 300K. The films were approximately 0.5μm thick and had nitrogen mole fraction between x=0.0014 and x=0.012, measured indirectly by a secondary-ion-mass spectrometry calibration; indium mole fraction between y=0.052 and y=0.075, measured by electron-dispersive x-ray spectroscopy; and carrier concentration between 2×1016 and 1.1×1018cm−3, measured by Hall effect. Three critical-point transitions were identified by PR: the fundamental band gap (highest valence band to the lowest conduction band); the spin-orbit split valence band to the lowest conduction band; and the highest valence band to a nitrogen impurity band (above the lowest conduction band). The measured critical-point energies were described by a band anticrossing (BAC) model with the addition of a Burstein-Moss band-filling term. The fitted BAC parameters were similar to previously reported values. The N impurity level was located 0.3004±0.0101eV above the conduction-band edge at 20K and 0.3286±0.0089eV above the conduction-band edge at 295K. The BAC interaction parameter was 2.588±0.071eV. From the small magnitude of the Burstein-Moss energy shift with increasing carrier concentration, it was inferred that the carrier concentration probed by PR is reduced from the bulk (Hall-effect) carrier concentration by a reduction factor of 0.266±0.145. The PR lines broadened with increasing carrier concentration; the line broadening tracked the predicted Burstein-Moss energy shift for the bulk carrier concentration. The surface-normal lattice constants of the films were measured by x-ray diffraction. Comparison of the measured lattice constants with Vegard’s law showed the presence of tensile strain (in the surface-normal direction) with magnitude between 1.5×10−3 and 3.0×10−3. The effect of strain on the PR energies was too small to observe. |
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ISSN: | 0021-8979 1089-7550 |
DOI: | 10.1063/1.2127126 |