Carrier concentration determination by photoreflectance at E 1 in thin film, highly doped GaAs

Photoreflectance (PR) response at the E1 (2.9 eV) transition of GaAs doped with Si, Zn, and Be was investigated within the range of 1.5×1015 to 2×1019 cm−3. Growth technique was either metalorganic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE). We find that Γ1, the broadening parameter of the E1 structure increases linearly with the logarithm of the measured carrier concentration over the range of ≊1×1017 to ≊1×1019 cm−3. A slope of 56±5 meV/decade describes all Si:GaAs samples independent of growth technique. For p-GaAs, the slope is 30±3 meV/decade over a comparable range and is independent of doping element as well as growth technique. This linear relation could be employed as a contactless means of determining carrier concentration. The energy position of E1 shows no significant shift in the above range. We believe that the broadening is a result of the doping produced, electric field within the depletion region.