Semi-insulating GaAs as well as MOCVD GaAs layers have been doped in situ with Se in a MOCVD system. H2Se diluted in an H2 + AsH3 atmosphere, which avoids surface decomposition, is used as the doping source. The surface is heated locally for less than 1 μs with a 3-ns Nd-YAG-laser pulse (frequency doubled: λ = 532 nm, pulse ratio 5 s−1). During this short time adsorbed Se atoms are incorporated into the heated surface region.
This process allows us to achieve heavily doped thin layers with Se concentrations in the order of 1021 cm−3. Outside the irradiated area the crystal remains undoped.
Se concentrations measured with secondary ion mass spectroscopy (SIMS) and carrier concentrations measured with the van der Pauw method indicate the diffusion of adsorbed Se atoms into GaAs. The distribution and activation of Se depends on laser power and substrate temperature.