Abstract

We report picosecond excite-probe and transient grating measurements on the alloy semiconductor GalnAsP with three different band gap energies. Pulses of 5-ps duration from a Nd:phosphate glass laser allowed excitation from band gap resonant conditions to excess energies of 0.3 eV. In the smallest gap materials, 0.86 eV, excite–probe measurements showed saturation and fast recovery within ~10 ps consistent with Auger recombination at carrier densities in excess of 2 × 10¹⁹ cm⁻³. Saturation of larger band gap samples (1.02 and 1.17 eV) occurred at lower laser fluences as expected, giving slower decays of ~500 ps due to radiative recombination but with an initially fast Auger component. Three pulse transient grating measurements used two excite pulses to produce a refractive grating of period 6 μm. The first-order diffraction of an orthogonally polarized probe pulse monitored the grating decay. All samples gave a decay rate of the same order ~200 ps which was faster than the decays associated with bimolecular recombination and is almost certainly due to ambipolar diffusion contributing to the washing out of the population modulation. We have thus demonstrated that nonlinear phenomena in these materials can have quite different band gap and carrier-dependent responses at 1.054 μm.

© 1986 Optical Society of America