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The bandgap, surface Fermi level, and surface state density of a series of GaAs1−xSbx surface intrinsic-n+ structures with GaAs as substrate are determined for various Sb mole fractions x by the photoreflectance modulation spectroscopy. The dependence of the bandgap on the mole composition x is in good agreement with previous measurements as well as predictions calculated using the dielectric model of Van Vechten and Bergstresser in Phys. Rev. B 1, 3551 (1970). For a particular composition x, the surface Fermi level is always strongly pinned within the bandgap of GaAs1−xSbx and we find its variation with composition x is well described by a function EF = 0.70 − 0.192 x for 0 ≦ x ≦ 0.35, a result which is notably different from that reported by Chouaib et al. [Appl. Phys. Lett. 93, 041913 (2008)]. Our results suggest that the surface Fermi level is pinned at the midgap of GaAs and near the valence band of the GaSb.

The metal-oxide-semiconductor metamorphic high-electron-mobility transistor (MOS-MHEMT) with an oxide grown by liquid phase oxidation on the InGaAs capping layer without a gate recess exhibits a lower leakage current density with suppressed impact ionization, better microwave characteristics, and improved high frequency noise performance compared to the conventional MHEMT with a recessed gate. The improved high frequency performance is due to the lower gate-source and gate-drain capacitances of the InAlAs/InGaAs MOS-MHEMT. Reduced surface recombination and impact ionization may also contribute to the improved frequency response, noise performance, and associated gain.

Room-temperature photoreflectance is employed to investigate the Fermi level pinning and surface state density of a GaAs0.65Sb0.35 surface intrinsic-n+ (SIN+) structure. Based on the thermionic emission theory and current-transport theory, the surface Fermi level VF and surface state density are determined experimentally from the dependence of the surface barrier height on the pump beam intensity. The surface state density Ds is estimated as approximately 1.91×1013 cm−2, and the Fermi level is located 0.63 eV below the conduction band edge at the surface. By sequential etching of the intrinsic layer, the Fermi level pinning in GaAs0.65Sb0.35 SIN+ structure is further demonstrated.

This study examines terahertz radiation from a series of In0.52Al0.48As and GaAs surface-intrinsic-N+ structures (SIN+) with surface-intrinsic layers of various thicknesses. The built-in electric fields in the SIN+ structures are used as the bias. Experimental results indicate that the amplitudes of the THz emission are independent of the built-in electric fields in the emitters when the built-in electric fields exceed the corresponding critical electric fields of the semiconductors. In contrast, the amplitudes of the THz emission are proportional to the thickness of the intrinsic layer and, therefore, the number of photo-excited charged carriers.

Room-temperature photoreflectance (PR) and photoluminescence (PL) spectra are measured for a series of In0.54Ga0.46P1−yNy∕GaAs heterostructures grown on GaAs (100) substrate. Redshifts of the PR and PL peaks indicate that the band gap of In0.54Ga0.46P1−yNy is dramatically reduced as nitrogen is incorporated. The emergence of additional peaks in PR spectra as nitrogen is incorporated indicates that the band alignment switches from type I to type II, due to the lowering of the conduction band, thus forming a two-dimensional electron gas (2DEG) in the interface region between In0.54Ga0.46P1−yNy and GaAs. The band gap energy and transition energies between the confined levels in the 2DEG are determined for samples with various nitrogen concentrations y. The number of confined levels in the 2DEG is found to increase with y; the composition-dependent bowing parameter is determined.