Vertical transport in GaAs/GaAlAs QW-GRIN structures studied by photocurrent spectroscopy

摘要

Abstract: GaAs/GaAlAs quantum well (QW) structures for graded index (GRIN) near IR injection lasers have been studied by polarization dependent photocurrent spectroscopy in the spectral region of QW transitions and in a wide range of temperatures 20 K $LSEQ T $LSEQ 375 K. The photocurrent has been measured under short-circuit conditions for the electric vector of the light wave parallel to the plane of the waveguide (TE) as well as perpendicular to the plane of the waveguide (TM). Distinct edges are observed in the quantum efficiency spectra and attributed to the onset of transitions form the heavy hole to electron and light hole to electron subbands, respectively. The observation of different spectral features in TE and TM spectra is discussed in terms of selection rules and mode coupling into the waveguide. Edge positions are compared with calculations of the well states. Coulomb interaction manifests itself in the occurrence of n $EQ 1 excitonic lines at the hh1-e1, 1h1-e1 and 1h2-e2 subband edges. Temperature dependent measurements indicate mechanisms for carrier escape form the QW. At intermediate temperatures the photocurrent is thermally activated, an explanation in terms of thermionic emission theory is given, and the justification of assuming thermalized non-equilibrium carriers is discussed for different transitions. The observed activation energy is correlated with the energy scale in the QW. At low temperatures the temperature dependence is weak, carrier escape is explained by tunnelling. At the highest temperatures the quantum efficiency decreases again, this is attributed to the growing influence of recombination. !22