Electron accumulation is found to occur at the surface of wurtzite ͑1120͒, ͑0001͒, and ͑0001͒ and zinc-blende ͑001͒ InN using x-ray photoemission spectroscopy. The accumulation is shown to be a universal feature of InN surfaces. This is due to the low ⌫-point conduction band minimum lying significantly below the charge neutrality level.

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We systematically investigate the influence of free-electron concentrations from 1.5×10 17 cm −3 up to 1.6×10 21 cm −3 on the optical properties of single-crystalline In 2 O 3 in the cubic bixbyite structure. Dielectric functions of bulk crystals and epitaxial films on various substrates are determined by spectroscopic ellipsometry from the mid-infrared (37 meV ≈ 300 cm −1) into the ultraviolet (6.5 eV) spectral region. Eight transverse optical phonon modes are resolvable for low carrier-density material. The analysis of the plasma frequencies yields effective electron masses which increase from a zero-density mass of m * = 0.18m 0 to 0.4m 0 at n = 10 21 cm −3. This mirrors the nonparabolicity of the conduction band being described by an analytical expression. The onset of absorption due to dipole-allowed interband transitions is found at 3.8 eV for n 10 19 cm −3. It undergoes a blue-shift (effective Burstein-Moss shift) for higher electron densities as a result of the dominating phase-space filling compared to band gap renormalization. A comprehensive model describing the absorption onset is developed, taking nonparabolicity into account, yielding an accurate description and explanation of the observations. The agreement of modeled and measured absorption onset independently supports the effective electron masses derived from infrared data. The high-frequency dielectric constant of undoped In 2 O 3 is found to be ε ∞ = (4.08 ± 0.02).

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Cubic InN layers were grown by plasma assisted molecular beam epitaxy on 3C-SiC (001) substrates at growth temperatures from 419to490°C. X-ray diffraction investigations show that the layers have zinc blende structure with only a small fraction of wurtzite phase inclusions on the (111) facets of the cubic layer. The full width at half maximum of the c-InN (002) x-ray rocking curve is less than 50arcmin. The lattice constant is 5.01±0.01Å. Low temperature photoluminescence measurements yield a c-InN band gap of 0.61eV. At room temperature the band gap is about 0.56eV and the free electron concentration is about n∼1.7×1019cm−3.