I. Mahboob

Clean wurtzite InN surfaces prepared with atomic hydrogen

Conventional methods of surface preparation for III–V semiconductors, such as thermal annealing and sputtering, are severely limited for InN, resulting in In-enrichment and the introduction of donorlike defects. This is explained in terms of the unusually low Γ-point conduction band minimum of InN with respect to its Fermi stabilization energy. Here, low energy atomic hydrogen irradiation is used to produce clean wurtzite InN surfaces without such detrimental effects. A combination of x-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy was used to confirm the removal of atmospheric contaminants. Low energy electron diffraction revealed a (1×1) surface reconstruction after cleaning. Finally, XPS revealed In∕N intensity ratios consistent with a predominantly In polarity InN film terminated by In-adlayers in analogy with c-plane GaN{0001}-(1×1) surfaces.

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.

Indium nitride: Evidence of electron accumulation

The electronic properties of clean InN(0001) surfaces have been investigated by high-resolution electron-energy-loss spectroscopy of the conduction band electron plasmon excitations and valence band x-ray photoemission spectroscopy. An intrinsic surface electron accumulation layer is found to exist, with the associated downward band bending occurring to neutralize charged donor-type surface states. Semiclassical dielectric theory simulations of the energy-loss spectra and charge profile calculations indicate a surface state density of 2.5(±0.2)×1013 cm−2 and a surface Fermi level of 1.64±0.10 eV above the valence band maximum and 0.89±0.10 eV above the conduction band minimum. This location of the surface Fermi level is in agreement with the valence band photoemission spectra. These observations are compared with recent evidence of electron accumulation at InN surfaces provided by capacitance–voltage profiling, Hall measurements, and synchrotron-radiation photoemission spectroscopy.

Core-level photoemission spectroscopy of nitrogen bonding in GaNxAs1−x alloys

The nitrogen bonding configurations in GaNxAs1−x alloys grown by molecular beam epitaxy with 0.07<x<0.11 have been studied using x-ray photoelectron spectroscopy (XPS). In contrast to previous studies of alloys with x⩾0.03, the nitrogen is found to exist in a single bonding configuration – the Ga–N bond; no interstitial nitrogen complexes are present. The amount of nitrogen in the alloys is estimated from the XPS using the N1s photoelectron and GaLMM Auger lines and is found to be in agreement with the composition determined by x-ray diffraction.

Effect of hydrogen in dilute InNxSb1−x alloys grown by molecular beam epitaxy

The electronic properties and nitrogen bonding configurations are investigated in dilute InNxSb1−x alloys grown by molecular beam epitaxy using a mixed nitrogen and hydrogen plasma. High-resolution electron-energy-loss spectroscopy is used to observe annealing-induced changes in the conduction band electron plasma frequency and plasmon lifetime. X-ray photoelectron spectroscopy of the N 1s core level indicates that a large proportion of the nitrogen in the InNxSb1−x alloy is contained within neutral N–H complexes. Annealing at 300 °C removes hydrogen from these complexes, increasing the concentration of isoelectronic nitrogen acceptors. This increases the ionized impurity scattering and reduces the background conduction electron density.

Low-energy nitrogen ion implantation of InSb

The modification of the electronic properties of InSb by implantation of low-energy N2+ ions and annealing have been investigated. A non-uniform electron density depth profile is observed in the near-surface region. Detailed measurements of the conduction-band electron-plasma frequency as a function of temperature combined with carrier statistics reveal that the electron concentration profile in the near-surface region cannot be explained solely by donor-type defects induced by the nitrogen implantation. However, these experimental observations can readily be explained in terms of InNxSb1−x band structure, the different distributions of damage-induced donor defects, and the acceptor-type nitrogen.

Electron spectroscopy of dilute nitrides

The application of electron spectroscopies in dilute nitride semiconductor research for both chemical analysis and the determination of electronic and lattice vibrational properties is described. X-ray photoelectron spectroscopy of the nitrogen bonding configurations in dilute InNxSb1−x and InNxAs1−x alloys is presented. High resolution electron-energy-loss spectroscopy (HREELS) of the plasmon excitations in InNxSb1−x is shown to provide information on the electronic properties of the material, before and after annealing. HREELS is also used to investigate the GaN-like phonon modes in GaNxAs1−x alloys.

Electron dynamics in InNxSb1–x

Electron transport properties in InNxSb1−x are investigated for a range of alloy compositions. The band structure of InNxSb1−x is modeled using a modified k⋅p Hamiltonian. This enables the semiconductor statistics for a given x value to be calculated from the dispersion relation of the E− subband. These calculations reveal that for alloy compositions in the range 0.001⩽x⩽0.02 there is only a small variation of the carrier concentration at a given plasma frequency. A similar trend is observed for the effective mass at the Fermi level. Measurements of the plasma frequency and plasmon lifetime for InNxSb1−x alloys enable the carrier concentration and the effective mass at the Fermi level to be determined and a lower limit for the electron mobility to be estimated.

Fuchs–Kliewer phonon excitations in GaNAs alloys

The surface optical phonon spectra of GaNxAs1−x alloys have been measured using high-resolution electron-energy-loss spectroscopy. Multiple excitations of both GaAs-like and GaN-like Fuchs–Kliewer phonons were observed. Comparison is made with surface optical phonon spectra obtained from GaAs and GaN, semiclassical dielectric theory calculations and previous Raman scattering measurements of bulk phonon spectra of GaNxAs1−x alloys.