ER IN MOLECULAR-BEAM EPITAXY-GROWN GAAS ALGAAS STRUCTURES/

Er-doped GaAs/AlGaAs structures were grown by the molecular beam epita xy technique with concentrations of Er in the range 10(17) - 2 x 10(19 ) cm(-3). Photoluminescence (PL) of Er3+ ions and Er-induced defects w as studied at liquid helium and higher temperatures. A strong diffusio n of erbium and interdiffusion of gallium and aluminum ions are observ ed [at the boundary of GaAs/AlGaAs quantum wells (QWs)] which leads at high erbium concentrations to degradation of the QW's and macroscopic (average) leveling of erbium and aluminum concentrations over the who le semiconductor structure. From high-resolution PL spectra the existe nce of three types of Er centers is deduced, which differ by positions of fine structure lines, PL lifetimes, and temperature dependence. Th e results indicate that these centers are accompanied by the appearanc e of three types of carrier traps with binding energies of 20, 50, and about 400 meV, respectively. The experiments show evidence that carri ers captured into these traps control the Auger excitation of Er ions assisted by multiphonon emission of local phonons. Temperature quenchi ng of erbium PL is controlled by depopulation of defect states in the case of Auger excitation via the most shallow hole trap (20 meV) and b y competition of multiphonon nonradiative capture with the Auger trans itions in the case of the deepest defect (400 meV). De-excitation proc esses of excited f electrons accompanied by generation of electron-hol e pairs were also considered. Such processes are especially important in the case of resonance excitation. Besides erbium PL at 1.54 mu m, P L of erbium ions was observed from upper excited states at 0.82 and 0. 98 mu m, which demonstrates the possibility of realizing a three-level scheme of light emission. (C) 1997 American Institute of Physics.