Influence of carbon doping on the photoconductivity in GaN layers

Carbon doped molecular beam epitaxy grown GaN layers exhibiting n-type cond uctivity were investigated by de photoconductivity measurements and optical admittance spectroscopy to determine the influence of deep defects on the dynamics of light induced conduction processes. The doping induces the form ation of a defect level at a photon energy of 40 to 70 meV below the bandga p becoming more pronounced with increasing carbon concentration. Simultaneo usly, the responsivity at 300 nm decreases with increasing power of the car bon filament caused by the incorporation of deep defects with an energy pos ition between 0.35 and 0.5 eV below band gap introduced by the doping proce ss. In parallel, the time constant of the persistent photoconductivity tau strongly decreases with increasing doping level correlated with a decrease in the concentration of defects at hv = 2.2 eV and 2.4 eV (yellow band) as observed by optical admittance spectroscopy. Our results evidence the direc t influence of deep defect levels on the photoconductive processes.