Raman scattering determination of free-carrier concentration and surface space-charge layer in 〈100〉 n-GaAs

We have used Raman scattering as a nondestructive, contactless method for determining not only the free-carrier concentration N but also the width of the space-charge layer in 〈100〉 n-GaAs with 4×1017 cm−3≤N≤1×1019 cm−3 using as an excitation several different wavelengths of an Ar+ laser. By comparing the intensity at different wavelengths of the uncoupled longitudinal optic phonon mode originating in the space-charge layer with the signal from a piece of undoped 〈100〉 material, it is possible to experimentally evaluate the width of the depletion layer Ls. We find that there is very good agreement between the experimental values and those obtained from a generalized theory for both degenerate and nondegenerate materials. Thus, these experimental results demonstrate that for 〈100〉 III-V semiconductors, Raman scattering can be used as a contactless method to determine the width of the space-charge region for carrier concentrations up to 1×1019 cm−3.