Optical and structural properties of GaAs grown on (100) Si by molecular-beam epitaxy

Abstract

GaAs epitaxial layers (0.5 μm<d<4 μm) were grown by molecular-beam epitaxy (MBE) on (100) Si substrates (2° off in 〈011〉 direction) by using the two-step growth mode. The structural properties of the grown films (lattice constants, misorientation, crystal quality) have been measured by high-resolution double-crystal x-ray diffraction. The GaAs layers are under biaxial tensile strain at temperatures below the growth temperature because of the difference in thermal expansion coefficients of GaAs and Si. With the use of temperature-dependent photoluminescence and excitation spectroscopy, the band edges as well as the dominant near-band-edge recombination processes have been determined. Excitonic resonances are clearly observed in the excitation spectra. The strain splitting between the heavy- and light-hole valence bands amounts to 13 meV at 4.5 K. The dominant low-temperature luminescence line at 1.489 eV is assigned to exciton-related recombination processes. In addition to the band-to-carbon acceptor (e,A0C) recombination at 1.470 eV, a defect-related (d,A0C) recombination process is identified at 1.411 eV for a sample temperature of 4.5 K. The defect concentration is higher near the GaAs to Si interface region and decreases with increasing GaAs layer thickness. With increasing temperature (80–300 K) the valence-band splitting diminishes and reaches a value of 9 meV at room temperature, in good agreement with the strain values determined by x-ray diffraction.