Excitonic electroabsorption spectra and Franz-Keldysh effect of In0.53Ga0.47As/InP studied by small modulation of static fields

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Abstract
The influence of electric fields on excitons and band states of a bulk semiconductor grown lattice matched to an n-InP substrate is studied by measuring absorption and differential electroabsorption spectra, i.e., by weak modulation of static fields. At small fields, field broadening of light- and heavy-hole excitons, split by residual strain, determines the shape of the electroabsorption spectrum. At slightly larger fields Franz-Keldysh oscillations of the band states develop, the discrete exciton lines disappear in the absorption spectrum and their electroabsorption signal becomes part of the response of the continuum. The transition from excitonic electroabsorption to the Franz-Keldysh effect is clearly resolved and both regimes are compared with theoretical models. The observable range of Franz-Keldysh oscillations increases linearly with the field which corresponds to a constant mean free path of free carriers of 160 nm and to a collision rate that increases with the square root of energy. Different reduced mass of light- and heavy-hole transitions leads to beat in the spectrum. For static fields above 10 kV/cm the electroabsorption spectra, in particular, the decay of the amplitude with increasing energy, is quantitatively described by the one-electron theory if an energy-dependent scattering rate accounts for a field-independent mean free path.