STRAIN RELAXATION IN HIGH-SPEED P-I-N PHOTODETECTORS WITH IN0.2GA0.8AS/GAAS MULTIPLE-QUANTUM WELLS

We have used high-resolution x-ray diffraction and photocurrent spectroscopy to investigate strain relaxation in In0.2Ga0.8As/GaAs multiple quantum wells and its influence on the optoelectronic and electronic properties of high-speed p-i-n photodetectors. In combination with numerical simulations and subband calculations, both methods allowed us to determine the degree of lattice relaxation. The results consistently show that lattice relaxation does not occur abruptly, but that the degree of relaxation increases gradually with increasing number of wells. In spite of the onset of lattice relaxation, these photodetectors exhibit a quantum efficiency of unity and recombination lifetimes in excess of 500 ps.