Radiative Lifetimes of Donor-Acceptor Pairs inp-Type Gallium Arsenide

The behavior of the low-temperature emission spectrum of $p$-type gallium arsenide with changes in temperature and excitation intensity has been observed. The band, usually at ∼1.49 eV (1.475 eV in germanium-doped samples), moves to higher energy as the pumping intensity or the temperature is increased. This behavior is consistent with a donor-acceptor-pair mechanism for the band. Radiative lifetimes and time-resolved spectra confirm this opinion. In high-purity crystals, the band decays in a fast but nonexponential manner, and the time-resolved spectra move steadily to lower energies as the delay after the pulse is increased. We believe these to be the first such measurements in gallium arsenide, and they firmly establish the origin of the 1.49-eV band. The properties of the decay are compared with those seen in GaP and CdS. The decay rate constant $W\left(0\right)\mathrm{}$ in GaAs is estimated to be about ${10}^3$ times greater than in GaP, and about the same as in CdS. The emission bands in the 1.50-1.51-eV region depend strongly upon the mode of excitation. The decay rates are high ($\tau <15\mathrm{}$ nsec). Such short decay times are consistent with the annihilation of excitons or free-electron-bound-hole recombinations.