Quantum Optoelectronics

Abstract:

The dynamics of photoexcited carriers in direct gap semiconductors can now be measured directly by time-resolved spectroscopy using intense, ultra-short laser pulses. High carrier densities can be generated and the processes of carrier cooling and recombination can be investigated by measuring band-edge transient absorption and luminescence. At high carrier densities a Mott transition is expected to occur when the interparticle separation r//s congruent 2. 5 a//o , where a//o is the exciton radius, so that for lower values of r//s dramatic changes in the band-edge absorption spectrum are expected. We report measurements of the layered semiconductor GaTe. The chief interest in this material is, as with other III-VI semiconductors, the strong excitonic behaviour exhibited at low temperature.

Abstract:

In this paper the authors show how picosecond time-resolved photoluminescence can be used to probe the energy relaxation of hot carriers in semiconductor structures. In addition, by measuring the variation of luminescence lifetime with carrier density one can obtain information about radiative and nonradiative decay processes. These processes are important in all photonic devices, but especially so in structures where interfaces may have a particularly strong influence.

Abstract:

We have studied the picosecond time dependence of luminescence from a two-dimensional electron system following absorption of an ultrashort light pulse. From our measurements we determine the temporal evolution of the carrier temperature, finding that the cooling of hot carriers is suppressed by a factor 60 below that predicted on a three-dimensional nondegenerate-electron model. Additionally, we determine the electron-hole radiative life-time and invoke a hole trap to explain shortened luminescence lifetimes at low carrier densities. © 1984 The American Physical Society.