Correlation of time-resolved electroluminescence and cathodoluminescence measurements on quantum well light emitters with varying barrier widths

Abstract

We present results of a comparative study of the time-dependent luminescence properties of multiple quantum well structures with varying barrier widths which are embedded in the active area of a light-emitting device. The carrier kinetics is investigated by different experimental approaches: Cathodoluminescence and electroluminescence experiments where excitation is on/off-modulated for the purpose of time-resolved measurements and time-resolved electroluminescence experiments in the small signal regime which allow for observation of the carrier kinetics under flatband conditions. Due to the exact determination of the excess carrier density the latter technique provides a sensitive tool for a precise estimation of the mono- and bimolecular recombination coefficients. Comparison with light output data yields radiative and nonradiative parts. We find that coupling of quantum wells dramatically favors nonradiative interface recombination as expected from a theoretical model accounting for the superlattice wavefunctions. On the other hand, the bimolecular recombination rate remains unaltered even when the barrier width is lowered from 18 to 0.9 nm. In contrast, on/off modulated experiments reveal that luminescence decay is strongly influenced by carrier drift out of the active area. A barrier width dependent carrier mobility in growth direction accounts for these results if phonon assisted hopping rather than Bloch transport is presumed. Thus, an estimation of device quality of quantum well light emitters by conventional time-resolved cathodo- (or photo-) luminescence experiments is found to be possible if internal field induced carrier drift processes are taken into account.

Dependence of Nanoelectronic-Structure Defect Detection by Cathodoluminescence on Electron Beam Current

“…The EL signal at room temperature for forward currents in similar InGaAs/GaAs laser diodes can be easily detected for injection current densities that may be comparable with current densities in local junction sites of our CL--measured structures [4]. The similarity of EL and CL spectra in the case of GaAs laser diodes has been attributed to the case of a single QW [5]. The defects observed in the investigated structures were identified as oval defects.…”

Visualizing Electron–Hole Separation in Photo-excited Polar Crystals

“…Understanding electron-hole separation caused by the internal electric field (E-field) is thus important and was analyzed by time-varying photo-luminescence spectra. 1) The intensity of the internal E-field was determined by measuring microwave radiation 2) in strained crystals that generated a piezoelectric E-field. Moreover, the effects of an internal E-field on carrier dynamics in polar crystals were measured in the sub-picosecond time scale, 3,4) which suggested that non-equilibrium carrier dynamics must be analyzed under the influence of an internal E-field.…”