Recombination Processes Responsible for the Room-Temperature Near-Band-Gap Radiation from GaP

A detailed study has been made of the near-band-gap (green) radiative-recombination processes in GaP at room temperature for carrier concentrations small compared to the band density of states. This study has shown that for crystals with nitrogen concentrations lower than ${10}^{17}$ ${\mathrm{cm}}^{-3\mathrm{}}$, free-exciton recombination is the dominant process independent of the doping type or level. At nitrogen concentrations greater than ${10}^{18}$ ${\mathrm{cm}}^{-3\mathrm{}}$, nitrogen-related processes dominate the recombination. The recombination is primarily through a bound-exciton mode; however, it is shown that approximately 30% of the recombination proceeds through a free-exciton mode. No evidence of a free-to-bound process involving the nitrogen electron trap has been found with an upper bound on its strength of 10%. Free-to-bound recombination involving P-site neutral donors is found to be important in the temperature range 80-150 °K, but is unimportant at 300 °K. The spectra presented are corrected for the system response and obtained in a manner that eliminates bulk-absorption distortion. The spectra in this work represent the true internal-emission energy distribution.