R. V. Kuz’menko

Temperature dependence of residual stress in epitaxial GaAs/Si(100) films determined from photoreflectance spectroscopy data

In the temperature range T=10–300 K, photoreflectance spectroscopy was used to study the temperature dependence of residual stress in epitaxial n-GaAs films (1–5 µm thick, electron concentration of 1016–1017 cm−3) grown on Si(100) substrates. A qualitative analysis showed that the photoreflectance spectra measured in the energy region of the E0 transition in GaAs had two components. They consisted of the electromodulation component caused by the valence subband |3/2; ±1/2〉-conduction band transition and the low-energy excitonic component. The magnitude of stress was determined from the value of the strain-induced energy shift of the fundamental transition from the subband |3/2; ±1/2〉 with respect to the band gap of the unstressed material E0(T)-E0|3/2; ±1/2〉(T). The increase in the energy shift E0-E0|3/2; ±1/2〉 from 22 ± 3 meV at 296 K to 29 ± 3 meV at 10 K, which was found in the experiments, gives evidence of an increase in biaxial stress with decreasing temperature.

Generalized multilayer model for the quantitative analysis of the electromodulation components of the electroreflectance and photoreflectance spectra of semiconductors in the region of the E0 fundamental transition

With the assumption of the Franz-Keldysh effect as the origination mechanism of the interband electromodulation E0 component, a generalized multilayer model of this effect was proposed. This model includes such physical parameters as the strength of the surface electric field and its decay profile in the space charge region, energy broadening, and partial modulation of the surface electric field. It was shown that the three regions can be defined in the simulated spectra, namely, the low-energy region, the region of main peak, and the high-energy region of the Franz-Keldysh oscillations. The effect of the model parameters on the line shape in these regions was studied. The ranges of the actual parameters were determined from the quantitative analysis of the experimental photoreflectance spectra of GaAs and InP substrates (n=1015 cm−3–1018 cm−3).

Combined photoreflectance/photoluminescence studies of the stability of semiconductor surface passivation

Combined photoreflectance/photoluminescence measurements are proposed for the study of the stability of semiconductor surface passivation. With such an approach, laser action on both charged and recombination-active electron states can be investigated. The efficiency of the method proposed is demonstrated with GaAs substrates passivated by selenium.

E0 photoreflectance spectra of semiconductor structures with a high density of interface states

The results of a photoreflectance spectroscopy study of Ga2Se3/n-GaAs samples prepared by long-term annealing of GaAs wafers (n≈1017 cm−3) in a Se-vapor atmosphere are presented. It was established that no photovoltage appears in the interface region of these structures under illumination. Photogeneration of the charge carriers in the substrate does not lead to a change in the Fermi level position at the interface, with only the depth of the space-charge region being modulated. The quantitative analysis of the spectra also indicates that the growth of a thick (∼ 1 µm) Ga2Se3 layer does not result in the expected shift of the Fermi level position in comparison to the natural oxide-covered surface.

Influence of laser pump density on the characteristic time constant and the intermediate-field electromodulation E0 component of the photoreflectance signal

The influence of the laser pump density L on the intensity and the characteristic time constant of the intermediate-field electromodulation E0 component of photoreflectance spectra in a direct-gap semiconductor was studied. The experiments were carried out using GaAs samples with carrier concentration n≈1016 cm−3 and laser pump densities in the range L=100 µW/cm2–1 W/cm2. For all of the samples under study, the logarithmic dependence of the intensity of the electromodulation signal on the laser radiation density was ascertained. No effect of the attendant variations of the characteristic time constant on the measured signal was observed.

A combined technique for studying the multicomponent spectra of photoreflection from semiconductors

A new technique for studying the multicomponent photoreflection spectra in semiconductors involves spectra measurements at different laser fluences and wavelengths in combination with spectrum phase analysis. To demonstrate the possibilities offered by the technique, the multicomponent photoreflection spectrum of the passivated homoepitaxial Si3N4/n-GaAs/n+-GaAs wafer is analyzed.

Combined photoreflectance/photoluminescence studies of the electronic properties of semiconductor surfaces

A technique involving combined photoreflectance/photoluminescence measurements is proposed to study the electronic properties of semiconductor surfaces. The efficiency of the technique is illustrated by a study of the growth and degradation of the luminescence signal from selenium-passivated GaAs substrates under CW laser excitation.

Low-energy oscillations in the E0 photoreflectance spectra of homoepitaxial n-GaAs/n+ -GaAs samples with n = 1015–1016 cm–3 and n+ ≈ 1018 cm–3

The nature of the long-wavelength region of the E0 photoreflectance spectra is studied in n - G aAs/ n + -GaAs homoepitaxial samples with n = 1015–1016 cm–3, n+ ≈ 1018 cm–3, and the epitaxial film width d = 1–5 μ m. The analysis of the published data, the quantitative analysis of experimental spectra, and our own experiments based on a novel technique, lead us to the conclusion that the low-energy oscillations originate in the electromodulation mechanism that takes place in the region of the film–substrate interface. The periodic modulation of the electric field near the film–substrate interface is induced by the isotropic diffusion of nonequilibrium minority carriers that are created in the neutral volume of epitaxial films under the action of laser excitation. The characteristic time constants of various photoreflectance components are estimated by combining the quantitative analysis of spectral line shapes with the analysis of experimental phase diagrams.

Electron states in the surface region of gallium arsenide treated in selenium and arsenic vapor

The parameters of charge localization centers in the skin layer of gallium arsenide treated in selenium-arsenic vapor are investigated by deep-layer transient spectroscopy. It is established that the addition of arsenic to the vapor phase slows down the reaction of heterovalent substitution of selenium for arsenic in GaAs and reduces the density of centers in the skin layer of GaAs.

Strain-induced photoreflectance spectra in the vicinity of the E0 transition in GaAs/Si and InP/Si heterostructures

A study is reported of the structure of photoreflectance (PR) spectra in the vicinity of the E0 transition from thin (d=1–5 µm) n-GaAs and n-InP films (n=1016–1017 cm−3) grown epitaxially on Si(001) substrates. A quantitative analysis of the spectra involving multi-component fitting shows that the electronic optical transition from the {3/2;±1/2} subband provides a dominant contribution to the intermediate-field electromodulation component in both systems. The splitting observed in the GaAS/Si PR spectra near the main peak are accounted for not by the strain-induced valence-band splitting but rather by a spectral superposition of the intermediate-field component due to the {3/2;±1/2} subband with a low-energy excitonic component. The analytically established transition energy E03/2;±1/2 is used to calculate biaxial strains in epitaxial films.