Red pair luminescence in GaP:Cu

Abstract

Investigations of the luminescent properties of high-ohmic Cu-doped GaP-crystals in the red spectral region (1.5-1.9 eV) with emphasis on broad band type emissions are reported. A dominant broad bell-shaped emission is found, centred at about 1.67 eV at 4 K. At low temperatures, this peak clearly shifts to higher energy with increasing excitation intensity, and non-exponential decay with emission persisting up to several minutes is observed. From those observations, the radiative mechanism for this emission at low temperatures sbelow ∼ 100 K) is believed to involve strongly phonon-coupled pair-transitions between (hallow donors and deep Cu-acceptors. The anomalous temperature dependence of the peak-energy position and emission intensity indicates that at higher temperatures (above ∼ 200 K) the radiative process involved is a transition between free elctrons and the same Cu-acceptor, also with strong phonon coupling. These observations imply a binding energy of 0.53 ± 0.03 eV for the corresponding Cu-acceptor. The excitation spectrum for this emission exhibits a dominant contribution from direct gap photon energies at low temperatures. Evidence for the existence of another Cu-related acceptor at about 0.7 eV above the valence band is also reported.