Luminescence decays of N-bound excitons in GsAs1-xPx

Abstract

We report photoluminescence-lifetime studies of nitrogen-bound excitons in GsAs1-xPx:N at low excitation power for 0.22<x≤1.0. Temperature was varied from T=1.8to200 K. A time resolution of 400 psec was obtained with the use of time-correlated single-photon counting. At low temperatures, a short (<10 nsec) nonexponential decay and a longer matrix-element-determined exponential decay are observed. Results prove that earlier 77-K phase-shift measurements gave information regarding only the nonexponential component. We report here on the true exponential luminescence lifetime. Luminescence-lifetime quenching as the temperature is raised from 1.8 to 40 K demonstrates that both A(J=1) and B(J=2) bound-exciton states exist in alloys with minimal strain mixing. Radiative lifetimes of both exciton spin states are obtained across the alloy for the first time and are compared with earlier theories. Both lifetimes show a bandstructure enhancement of 2 orders of magnitude, with A-state radiative lifetimes varying from about 100 nsec in GaP to 1 nsec for x=0.23. When the bound exciton is near resonance with the direct edge (for x≅0.22), the radiative lifetime approaches but does not fall below the direct-edge luminescence lifetime, thus showing that the recombination rate does not diverge with resonance. For T>40 K, two distinct thermal processes occur, one of which (hole release) increases the luminescence lifetime, while the other (electron detrapping) decreases the lifetime and quenches the luminescence intensity. Observation of hole release confirms the Hopfield-Thomas-Lynch model of N isoelectronic traps, and proves for the first time that isolated N binds a bare electron. © 1983 The American Physical Society.