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By the optical phase-shift technique measurements are made (77°K) of excess carrier lifetimes on ``surface-free'' thin layers of lightly doped n- and p-type GaAs, and on damage-free vapor-grown thin blades. The nonradiative losses due to surface recombination are minimized by selectively photoexciting the center layer of a GaAlAs(n+)/GaAs(n or p)/GaAs(n+) structure through the first layer, which acts as a window and as a confining barrier of excess carriers. The spontaneous carrier lifetime (δn∼1016/cm3) for surface-free epitaxial layers of n-type GaAs (ND-NA=2.42×1015 cm−3) and for p-type GaAs (NA-ND=4.64× 1016 cm−3) at 77°K is 4.1 and 4.3 nsec, respectively, which is to be compared with a value of 1.9 nsec for a thin damage-free vapor-grown blade not seeded on a substrate.
Keune et al. (Thu,) studied this question.