Composition and carrier-concentration dependence of the electronic structure of In{sub y}Ga{sub 1-y}As{sub 1-x}N{sub x} films with nitrogen mole fraction of less than 0.012

• Published in: Journal of applied physics 2005-11, Vol.98 (9)
• Main Authors: Kang, Youn-Seon, Robins, Lawrence H., Birdwell, Anthony G., Shapiro, Alexander J., Thurber, W. Robert, Vaudin, Mark D., Fahmi, M.M.E., Bryson, Damian, Mohammad, S. Noor, Materials Science Research Center of Excellence, Howard University, Washington, DC 20059
• Format: Article
• Language: English
• Subjects: CALIBRATION; CARRIER DENSITY; DOPED MATERIALS; ELECTRONIC STRUCTURE; ENERGY GAP; GALLIUM ARSENIDES; GALLIUM NITRIDES; HALL EFFECT; INDIUM NITRIDES; ION MICROPROBE ANALYSIS; L-S COUPLING; LATTICE PARAMETERS; LINE BROADENING; MASS SPECTROSCOPY; MATERIALS SCIENCE; MOLECULAR BEAM EPITAXY; NITROGEN; SEMICONDUCTOR MATERIALS; SILICON; X-RAY DIFFRACTION; X-RAY SPECTROSCOPY
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.2127126

The electronic structure of Si-doped In{sub y}Ga{sub 1-y}As{sub 1-x}N{sub x} films on GaAs substrates, grown by nitrogen-plasma-assisted molecular-beam epitaxy, was examined by photoreflectance (PR) spectroscopy at temperatures between 20 and 300 K. The films were approximately 0.5 {mu}m 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 2x10{sup 16} and 1.1x10{sup 18} cm{sup -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{+-}0.0101 eV above the conduction-band edge at 20 K and 0.3286{+-}0.0089 eV above the conduction-band edge at 295 K. The BAC interaction parameter was 2.588{+-}0.071 eV. 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 1.5x10{sup -3} and 3.0x10{sup -3}. The effect of strain on the PR energies was too small to observe.