LOCALIZATION EFFECTS, ENERGY RELAXATION, AND ELECTRON AND HOLE DISPERSION IN SELECTIVELY DOPED NORMAL-TYPE ALYGA1-YAS/INXGA1-XAS/GAAS QUANTUM-WELLS

The nonequilibrium electron-hole pair (e-h) system in a strained InxGa1-xAs quantum well (QW) has been studied. The heterostructures were selectively doped n-type AlyGa1-yAs/ InxGa1-xAs/GaAs (x=0.1 0.2) having an electron concentration n2D=(0.4 1.0)×1012 cm-2. Simultaneous measurements of the quantum Hall effect and photoluminescence in a magnetic field were found to be crucial to obtain a reliable understanding of the system. The main features of the emission spectra from a weakly excited QW (the concentration of photoexcited e-h pairs is less than 1011 cm-2) were found to be determined by hole localization due to fluctuations in the InxGa1-xAs composition ( x/x<1%), QW thickness ( Lz/Lz)<5%, and the density of charged impurities. The hole relaxation time was found to depend on the excited e-h pair density and QW quality. At the low excitation density of 10-3 W/cm2 the hole temperature reaches 20 K at a lattice temperature of 2 K. Finally, the E-k dispersion of electrons and holes were measured from the emission spectra under magnetic field. The electron effective mass was determined to be 0.072m0 and 0.067m0 for QWs with x=0.13 and 0.18, respectively. The valence band is strongly nonparabolic with the hole mass 0.105m0 at the band edge. © 1990 The American Physical Society.