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We describe two mechanical light chopper blade designs that can be used, with a monochromator and broadband light-source-based spectroscopy setup, to perform wavelength modulation spectroscopy. The left and the right half of a beam emerging from a monochromator would have spectral distributions that are skewed to longer and shorter wavelengths about the central wavelength for positive grating orders. Our two designs, the alternating double-slot blade and the vertical right-angled blade, allow switching between the two halves of the beam front to generate a small periodic variation in the wavelength distribution, enabling wavelength modulation spectroscopy. In contrast to existing methods of wavelength modulation, this technique does not require modification of the monochromator or the light source unit. We analyze the signal waveforms and show how, and under what conditions, wavelength modulation data can be extracted from the alternating signal components measured by the detector. To demonstrate their functioning and applicability, we have performed wavelength-modulated reflectance spectroscopy on epitaxial semiconductor samples using these chopper blades. [ABSTRACT FROM AUTHOR]

Measurements of electroreflectance and surface photovoltage spectroscopy of semiconductor structures are described using a transparent indium-tin-oxide-coated glass electrode in soft contact mode on the semiconductor surface. This improvisation (simplification) reduces the magnitude of the ac modulation voltage necessary for the electroreflectance measurement to less than a volt from about a kV (∼103 V) as required in the conventional contactless setup. This soft contact mode also enhances the sensitivity of the surface photovoltage signal by three orders of magnitude. We also formulate an analytical criterion to extract the transition energies of a quantum well from the surface photovoltage spectrum. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The effect of alloy fluctuations on the emission barrier of the DX center in aluminum gallium arsenide (AlGaAs) is studied by constant capacitance deep level transient spectroscopy using Si-doped and Sn-doped samples grown by different growth techniques. All the samples showed single broadened peaks which were analyzed by assuming a Gaussian distribution for the emission barrier. The full width at half maximum for the emission barrier spread was found to be the same (∼0.05+0.005 eV) for all the samples and is of the same order as the reported capture barrier spread for Si-doped AlGaAs, which strongly suggests that the binding energy spread of the DX center in AlGaAs is very small. [ABSTRACT FROM AUTHOR]

Surface photovoltage (SPV) of n-GaAs decreases both above and below a certain transition temperature. We explain this phenomenon in terms of a Schottky contact based model and relative dominance of thermal and nonthermal parts of the dark current. This also explains the observed increase of SPV of p-GaAs below room temperature. Our analysis is further confirmed from the temperature dependence of the SPV measurements on p-InP and n-InP samples. Surface passivation is seen to lower the transition temperature of n-GaAs. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]