P. H. Jefferson

Transition from electron accumulation to depletion at InGaN surfaces

The composition dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1−xN films (0⩽x⩽1) is investigated using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band minimum (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approximately x=0.3. The results are consistent with the composition dependence of the band edges with respect to the charge neutrality level.The composition dependence of the Fermi-level pinning at the oxidized (0001) surfaces of n-type InxGa1−xN films (0⩽x⩽1) is investigated using x-ray photoemission spectroscopy. The surface Fermi-level position varies from high above the conduction band minimum (CBM) at InN surfaces to significantly below the CBM at GaN surfaces, with the transition from electron accumulation to depletion occurring at approximately x=0.3. The results are consistent with the composition dependence of the band edges with respect to the charge neutrality level.

Photoluminescence spectroscopy of bandgap reduction in dilute InNAs alloys

Photoluminescence (PL) has been observed from dilute InNxAs1–x epilayers grown by molecular-beam epitaxy. The PL spectra unambiguously show band gap reduction with increasing N content. The variation of the PL spectra with temperature is indicative of carrier detrapping from localized to extended states as the temperature is increased. The redshift of the free exciton PL peak with increasing N content and temperature is reproduced by the band anticrossing model, implemented via a (5×5) k·p Hamiltonian.

Band anticrossing in GaNxSb1–x

Fourier transform infrared absorption measurements are presented from the dilute nitride semiconductor GaNSb with nitrogen incorporations between 0.2% and 1.0%. The divergence of transitions from the valence band to E– and E+ can be seen with increasing nitrogen incorporation, consistent with theoretical predictions. The GaNSb band structure has been modeled using a five-band k·p Hamiltonian and a band anticrossing fitting has been obtained using a nitrogen level of 0.78 eV above the valence band maximum and a coupling parameter of 2.6 eV.

Band gap reduction in GaNSb alloys due to the anion mismatch

The structural and optoelectronic properties in GaNxSb1−x alloys (0⩽x<0.02) grown by molecular-beam epitaxy on both GaSb substrates and AlSb buffer layers on GaAs substrates are investigated. High-resolution x-ray diffraction (XRD) and reciprocal space mapping indicate that the GaNxSb1−x epilayers are of high crystalline quality and the alloy composition is found to be independent of substrate, for identical growth conditions. The band gap of the GaNSb alloys is found to decrease with increasing nitrogen content from absorption spectroscopy. Strain-induced band-gap shifts, Moss-Burstein effects, and band renormalization were ruled out by XRD and Hall measurements. The band-gap reduction is solely due to the substitution of dilute amounts of highly electronegative nitrogen for antimony, and is greater than observed in GaNAs with the same N content.

X-ray photoemission spectroscopy determination of the InN/yttria stabilized cubic-zirconia valence band offset

The valence band offset of wurtzite InN(0001)/yttria stabilized cubic-zirconia (YSZ)(111) heterojunctions is determined by x-ray photoemission spectroscopy to be 1.19±0.17eV giving a conduction band offset of 3.06±0.20eV. Consequently, a type-I heterojunction forms between InN and YSZ in the straddling arrangement. The low lattice mismatch and high band offsets suggest potential for use of YSZ as a gate dielectric in high-frequency InN-based electronic devices.

Dilute Antimonide Nitrides for Very Long Wavelength Infrared Applications

The addition of small amounts of nitrogen to III-V semiconductors leads to a large degree of band-gap bowing, giving rise to band-gaps smaller than in the associated binary materials. The addition of a small percentage of nitrogen to GaSb or InSb is predicted to move their response wavelengths into the long or even very long wavelength IR ranges. We report the growth of GaNxSb1-x by MBE, using an r.f. plasma nitrogen source, examining the influence of plasma power, substrate temperature and growth rate. We demonstrate high structural quality, as determined by x-ray diffraction, and show a reduction in band-gap by over 300meV, compared with GaSb, based on FTIR transmission spectroscopy. We also report initial experiments on the growth of InNxSb1-x and Ga1-yInyNxSb1-x, with a view to extending the response into the long and very long wavelength IR ranges.

Growth and characterisation of dilute antimonide nitride materials for long-wavelength applications

The addition of small amounts of nitrogen to III-V semiconductors leads to a large degree of band gap bowing, giving rise to band-gaps smaller than in the associated binary materials. The incorporation of active nitrogen has been previously demonstrated for InNxSb1-x (x≤0.7%) and GaNxSb1-x (x≤1.75%) material; however, the as-grown carrier concentrations precluded incorporation into a device structure. Here we report the reduction in the as-grown carrier concentration in InNSb by annealing, whilst retaining the active nitrogen content. FTIR absorption measurements show the first direct experimental evidence of narrowing of the InSb bandgap due to nitrogen incorporation. As an alternative route to defect reduction and device compatible material we report on the growth of Ga1-yInyNxSb 1-x with 0≤y≤30% and x=1.6±0.2% and demonstrate near lattice matching of the material to GaSb.