Photoreflectance study of photovoltage effects in GaAs diode structures (original) (raw)
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Photoreflectance study of GaAsSb∕InP heterostructures
Journal of Applied Physics, 2005
Photoreflectance (PR) spectroscopy experiments are reported on GaAsSb∕InP heterostructures. The GaAsSb PR spectrum is studied as a function of temperature and the transition nature is shown to change from Franz-Keldysh oscillations (FKO) at room temperature to a third derivative functional form (TDFF) line shape at low temperatures. Combining both analysis (FKO and TDFF) in the same sample, we derive internal electric field and phase values of the PR transition, together with accurate values for alloy band gap energy on the whole temperature range. Type II interface recombination is shown to reduce photovoltage effects as a function of temperature. FKO are found to appear for a very weak electric field (8kV∕cm) in the GaAsSb∕InP heterostructure, contrary to usual observations. This point is discussed in relation with the broadening parameter of the transition.
Journal of Electron Spectroscopy and Related Phenomena, 1998
We used the SuperACO Free Electron Laser (FEL) to excite photocarriers in semiconductors at room temperature, and synchrotron radiation photoemission spectroscopy to measure the consequently induced surface photovoltage (SPV). The natural synchronization between the two sources allowed us to study with sub-nanosecond resolution the temporal dependence of the non-equilibrium charge carrier distribution for two prototype systems, Ag/GaAs(110) and Si(111)2×1. We found that to correctly interpret the effects of the SPV on the band position, the interplay between instrumental factors (pulse duration and repetition rate) and semiconductor parameters (such as surface and bulk recombination rates) must be taken into account. Since the FEL has the typical temporal structure of a synchrotron radiation source and a flux comparable to the one obtainable at third generation storage rings, these results are of relevance to the most advanced spectroscopic techniques used to study the electronic structure of semiconductors; therefore, in this paper we discuss the possible effects of intense synchrotron radiation beams on position and lineshape of photoemission features at semiconductor surfaces.
Physical Review B, 1990
Soft x-ray photoemission spectroscopy measurements of Fermi-level positions within the band gap of clean, GaAs(100) surfaces demonstrate that photovoltaic charging produces a major shift in the apparent band bending at low (50-100 K) temperatures. These measurements confirm recent predictions of Hecht [M. H. Hecht, Phys. Rev. B 41, 7918 (1990)], based on restoring currents limited by carrier transport through the depletion region, highlight the e6'ects of photovoltaic charging for clean (versus metallized) semiconductor surfaces, and justify Hecht's claims for a reassessment of many previous low-temperature photoemission studies of Fermi-level movement.
Surface Science, 2001
A new model is proposed in order to interpret the surface dependence of the constant and modulated photovoltages in a photore¯ectance spectroscopy experiment, with a particular emphasis on low temperature conditions, at which the time of establishment of equilibrium between surface and bulk is very long. In this model, the constant photovoltage depends on the eciency of surface recombination, while the modulated photovoltage is related to the modulation of this eciency induced by the modulation of the surface Fermi level. This model is illustrated by the photovoltage changes induced by formation of a metallic phase under adsorption of Na and K on GaAs(0 0 1). At a coverage situated between 0.5 and 1 ML, there ®rst occurs an increase of the modulated photovoltage, followed by a decrease, whereas the constant photovoltage exhibits a featureless abrupt decrease, due in the same way to discharging of the surface by metallic transport to surface defects. The increase of the modulated photovoltage is caused by the metallic surface phase, and is qualitatively explained by the above simple model, in which the modulated photovoltage changes depend on the total number of metallic states which pin the Fermi level.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2000
Ionizing radiation can be detected by the measurement of the charge carriers produced in a detector. The improved semiconductor technology now allows detectors operating near the physical limits of the detector materials to be designed. The mean energy required for producing an electron}hole pair, =, is a material property of the semiconductor. Here, the determination of = from the spectral responsivity of photodiodes is demonstrated. Using spectrally dispersed synchrotron radiation, di!erent types of semiconductor photodiodes have been examined in the UV-, VUV-, and soft X-ray spectral range. Their spectral responsivity was determined with relative uncertainties between 0.4% and 1% using a cryogenic electrical-substitution radiometer as primary detector standard. Results are presented for silicon n-on-p junction photodiodes and for GaAsP/Au Schottky diodes at room temperature. The investigations for silicon covered the complete spectral range from 3 to 1500 eV, yielding a constant value ="(3.66$0.03) eV for photon energies above 50 eV, a maximum value of ="4.4 eV at photon energies around 6 eV, and a linear relation ="h (one electron per photon) for photon energies below 4 eV. For GaAsP, we obtained a constant value of ="4.58 eV in the photon energy range from 150 to 1500 eV, with a relative uncertainty of 1}3%, depending on the photon energy.
Photoemission study of LT-GaAs
Journal of Alloys and Compounds, 2004
The electronic structure of GaAs (1 0 0) grown by low-temperature molecular beam epitaxy was investigated by means of photoemission spectroscopy. Slight differences are found in the valence band spectra of GaAs layers grown at different As 2 /Ga flux ratios. Analysis of As 3d core level spectra does not indicate qualitative differences in respect to high temperature grown GaAs (1 0 0) layers. The Ga 3d core level spectra include a new component in comparison to the spectra of high temperature grown GaAs. The origin of this component is attributed to high density of As antisites in low-temperature grown GaAs.
Method for calculating photo- and electroreflectance spectra from semiconductor heterostructures
Physical Review B, 1995
A method for calculating photoand electrore8ectance spectra from weakly inhomogeneous layers of semiconductor heterostructures is developed. Transfer matrices are used in order to solve the propagation of light between di8'erent layers and perturbation theory in order to obtain the transfer matrix for a single layer. If applied to an infinite half space, the method reproduces the result by Aspnes and Frova [Solid State Commun. 7, 155 (1969)I. The electric field profiles of the heterostructures are calculated by means of an integral equation which holds under quite general conditions including incomplete dopant ionization and carrier degeneracy. The application of the general theory is demonstrated by calculating photore8ectance spectra of homogeneously n-doped semi-infinite GaAs samples with difFerent doping levels, and of a (Al, Ga)As heterostructure with an interface charge between bu8'er layer and substrate. Due to its speed and accuracy the method has the potential for an on-line simulation of photoand electrore8ectance spectra.