Characterization of Dominant Recombination Centers in Semiconductors from the Temperature Dependence of Luminescence Excitation Spectra: GaP(Zn,O)

A new optical method is presented for determining the binding energies, capture coefficients, and branching ratios of dominant recombination centers (both radiative and nonradiative) in a luminescent semiconductor. It is shown that the temperature dependence of the photoluminescence excitation (PLE) spectrum of a radiative center can be used as a sensitive probe of changes in the minority-carrier recombination current as the dominant centers thermalize, or as nonradiative Auger processes become important at elevated temperatures. Using a very general steady-state model of the recombination kinetics, the PLE temperature dependence can be analyzed to extract information characterizing and identifying those centers which limit the luminescent quantum efficiency and minority-carrier lifetime of the material. Application of the PLE method is made to solution-grown GaP(Zn, O), where information is obtained on five major recombination centers. Evidence is presented which suggests that between 100-200 ^∘{}K electron capture at the Zn-O center and the other dominant (nonradiative) center proceeds by means of an Auger process. Below 60 ^∘{}K, approximately 90% of the minority-carrier recombination is found to occur at inadvertent sulfur and nitrogen centers. The ionized sulfur donor is estimated to have a "giant" capture cross section of order 10^-10 cm² at 54 ^∘{}K, and is therefore a dominant trapping center in GaP. Thermal quenching of the oxygen-donor luminescence is also observed, resulting from the thermalization of a shallow excited state active in the electron-capture process.