Optical Phase-Shift Measurement of Carrier Decay Times (77°K) on Lightly Doped Double-Surface and Surface-Free Epitaxial GaAs

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.