Electro-optical modulation properties of GaAs doping superlattices

Modulated transmission and reflectance measurements have been performed on a number of MOCVD grown structures of the type p⁺-x-n⁺ where x is either an undoped layer of GaAs, a GaAs doping superlattice, or a compensated layer of GaAs. The structures have been characterized by I/V, C/V and photoluminescence measurements. For the doping superlattices, with individual layer thicknesses of between 18 and 70 nm and doping levels of 10¹⁸/cm³, the superposition of the externally applied field on the large built-in field allows very high internal fields to be applied over a limited region of the sample. In this way, fields of up to approx. 500 KV/cm have been applied. For photon energies close to the bandgap of GaAs, the modulation properties of the structures are consistent with a Franz-Keldysh mechanism up to the highest internal electric fields, with no evidence for the anomalous behavior reported elsewhere.