EXCITONIC ELECTROABSORPTION SPECTRA AND FRANZ-KELDYSH EFFECT OF IN0.53GA0.47AS INP STUDIED BY SMALL MODULATION OF STATIC FIELDS/

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 broade ning of light- and heavy-hole excitons, split by residual strain, dete rmines the shape of the electroabsorption spectrum. At slightly larger fields Franz-Keldysh oscillations of the band states develop, the dis crete exciton lines disappear in the absorption spectrum and their ele ctroabsorption signal becomes parr of the response of the continuum. T he transition from excitonic electroabsorption to the Franz-Keldysh ef fect is clearly resolved and both regimes are compared with theoretica l models. The observable range of Franz-Keldysh oscillations increases linearly with the field which corresponds to a constant mean free pat h of free carriers of 160 nm and to a collision rate that increases wi th the square root of energy. Different reduced mass of light- and hea vy-hole transitions leads to beat in the spectrum. For static fields a bove 10 kV/cm the electroabsorption spectra, in particular, the decay of the amplitude with increasing energy, is quantitatively described b y the one-electron theory if an energy-dependent scattering rare accou nts for a field-independent mean free path. [S0163-1829(98)04639-6].