Recombination Kinetics in GaP Red-Emitting Diodes Determined by Photocurrent and Decay Characteristics

The photocurrent characteristic of GaP red light-emitting diodes excited in the band centered at 5900 Å below the band edge at room temperature was studied in a temperature range of 170–500°K. The characteristic band is explained in accordance with the thermal release of electrons from optically excited excitons bound to the Zn–O nearest neighbor pairs to the conduction band. The Zn–O pair concentration in the light-emitting region is determined accurately by analysing the results, The time-decay characteristics of the red electroluminescence were also measured to obtain the transition rates of electrons trapped at the Zn–O centers. At room temperature, the thermal release rate of electrons W_II is 1.8±0.2×10⁶ sec^-1 and the electron capture cross section of the Zn–O center is deduced to be 5.9±1.5×10^-16 cm² by using the observed binding energy of the center 300±10 meV. The radiative recombination rate W_I and the non-radiative recombination rate W_III are estimated to be 1.6×10⁶ and 2.4–3.4×10⁶ sec^-1, respectively. W_III seems to be determined by Auger process and depends largely on the free hole concentration in the active p region.