Optical Characterization of GaAs Layers Grown on Ge Substrates

The structural quality of GaAs layers grown on Ge substrates has been optically characterized as a function of the distance d from GaAs ‐ Ge interface along the growth axis, supported by electrical measurement and also by x‐ray measurement. It is found that the degradation of the structural quality due to interface alloying and autodoping of Ge can be detected in the grown layers only within ∼3μ from the interface, where the concentration of Ge involved would exceed 1 × 10 17 atoms / cm 3 . However, the degradation caused by misfit dislocations extends as far as 80μ from the interface, in spite of the fact that the dislocation density decreases exponentially with increasing d . These misfit dislocations introduce quite effective nonradiative recombination centers in GaAs , which quench the luminescence intensity, L , in a form of L = A log ( 1 × 10 6 / N ) , where N is the density of these nonradiative recombination centers and A is a constant. If the GaAs layers are contaminated with Cu during the growth process, it is found that L is reduced in such a way that the constant A in the above equation is decreased.