Optical and electro-optical investigation of low-temperature grown GaAs

We report on the effects of growth temperature, arsenic source and post growth annealing treatment on the optical properties of low temperature grown GaAs. We have determined the absorption coefficient over a wide spectral range of energies between 0.8 and 2.0 eV. Special interest was dedicated to the shape of the band edge absorption for the different growth conditions and post growth treatments. The band edge is sharper for samples grown with an As4 source than for samples grown using As2. However, the band edge becomes sharper due to the annealing process for all samples. A sharp band edge is essential for a high-contrast electro-optical modulator. We also measured the electro-absorption of a metal-semiconductor-metal structure based on annealed LT-GaAs and achieved a contrast ratio of 1:1.35 corresponding to an absorption change of 2300 cm−1.