A quantitative full‐fitting analysis of photoreflectance (PR) spectra in the region of the fundamental energy gap E0 from MBE n‐GaAs layer structures (n = 5 × 1015 to 1017 cm−3) on n‐GaAs is performed. They exhibit a complex spectral behaviour consisting of Franz‐Keldysh oscillations, and excitonic structure near E0, and for high‐energetic interference oscillations (LEIO). Spectra are measured using pump beam wavelengths of 488 and 633 nm with modulation frequencies between 167 Hz and 1.42 kHz and pump power densities from 2 × 10−3 to 2 W/cm2. Amplitudes and lineshapes of the three components are shown to vary strongly with changes in the excitation conditions and the phase of the synchronously detected signal which allows to investigate the effect of partial modulation and temporal behaviour of the field modulation mechanisms.
The stress‐induced behavior of E0 photoreflectance (PR) spectra of strained III–V epilayers in n‐GaAs/Si and n‐InP/Si heterostructures is studied. Expected effects of residual biaxial layer stresses σ∥ on spectral shape and energetic position of the E0 PR features are simulated by model calculations for medium‐field as well as low‐field PR spectra. Experimental PR spectra are analyzed with the aid of quantitative lineshape fitting. The full fitting analysis reveals energetically shifted heavy hole (hh) transitions as dominant spectral constituent in the stress‐induced PR spectra and provides reliable values E0hh of hh transition energies under strain. The shift of E 0hh is used to evaluate the value of the layer stress σ∥.
Photoreflectance (PR) modulation spectroscopy is a widely used optical technique on GaAs but it has been applied much more rarely on InP being an equally important optoelectronic compound semiconductor. Typical PR spectral lineshapes in the fundamental gap region of various InP materials are investigated. Spectral components such as Franz-Keldysh oscillations, lowfield features, and epilayer interference phenomena are analyzed. Current applications concern the determination of the surface electric field, investigations of ion etching and hydrogenation processing, and the characterization of homo-and strained heteroepitaxial layers by means of synchronous phase and complex fitting analysis.
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