Computer simulation of the photoluminescence decay at the GaAs-electrolyte junction. 1. The influence of the excitation intensity at the flat band condition

Abstract

The influence of excitation intensity, surface recombination velocity, and photocunent on the time-resolved photoluminescence (PL) at the nlGaAs-electrolyte junction under flat band conditions was investigated using computer simulations. The mathematical background of the two-dimensional semiconductor analysis package (TOSCA) will be presented. We will show that the effects may be characterized qualitatively by exponential fit function(s), although in most cases the simulated PL decay is nonexponential. For a free carrier concentration no = 5 x 1017 cmP3, under the conditions of low injection density (pi) and with flat bands, both the surface recombination and the photocurrent lead to a remarkable decrease in the PL decay time either for surface recombination velocities SO > lo3 cm/s or for exchange photocurrent densities j@,O > lo-'' A/cm2. Under the conditions chosen in this work, the PL decay time approximated by the monoexponential decay time T decreases to a minimum value in Tfin = 1.64 ns when SO I lo6 cm/s or jph,O L lov8 A/cm2. This minimum indicates that the diffusion of the minority carriers toward the surface where they immediately nonradiatively vanish by means of surface recombination and/or charge transfer, respectively, is limited by the thermal velocity. In both cases, diffusion competes effectively against bulk recombination. For injection levels (p,/no) > 0.1, the PL decay time decreases with increasing injection density because the quadratic recombination process dominates. At high injection densities, the surface recombination velocity may not remain constant during the PL decay, but instead varies as a function of time S(t); S may decrease from its maximum value (SO) by up to 1 order of magnitude during the PL decay. The results will be discussed in relation to experimental results published previously by other groups.

Behavior of Si Photoelectrodes under High Level Injection Conditions. 2. Experimental Measurements and Digital Simulations of the Behavior of Quasi-Fermi Levels under Illumination and Applied Bias

“…The simulation of specific electrical contacts (e.g., gate or ohmic) is accomplished by the imposition of suitable boundary conditions. A more detailed description of the mathematical and physical models used in ToSCA can be found in a previous publication and references therein …”

Surface Recombination Kinetics at the GaAs/Electrolyte Interface via Photoluminescence Efficiency Measurements

“…[18][19][20] Under these circumstances, the surface is a sink for minority carriers, and band unbending is difficult to achieve because the facile loss mechanism increases the required injection rate even further. Yet this picture is inconsistent with recent studies of the GaAs/ electrolyte interface, 16, [21][22][23][24][25][26][27][28][29] which suggest that the detailed kinetics of surface recombination has a significant influence on carrier dynamics near the GaAs/electrolyte surface.…”

Conditions Under Which Heterogeneous Charge-Transfer Rate Constants Can Be Extracted from Transient Photoluminescence Decay Data of Semiconductor/Liquid Contacts As Determined by Two-Dimensional Transport Modeling

“…Equations similar to eqs 10-12 have been used previously to provide boundary conditions for the simulation of photoluminescence decay data using ToSCA. 33,38,51,63 Such steady-state equations do not, however, adequately describe the photoluminescence decay dynamics under all of the conditions of concern in this study. Under steady-state conditions, that is, when the lifetime for the change of trap occupancy is small compared to all other electrical and thermal carrier generation and capture processes, the steady-state Shockley-Read-Hall treatment provides an accurate description of the recombination kinetics for both carrier types with respect to midgap recombination sites.…”

“…The ToSCA program and its validation with respect to analytical solutions available for several limiting carrier injection and electrode bias combinations have been described in detail previously. 51 For this study, the ToSCA code was extended in several important respects. A trapping model for majority and minority carriers was incorporated to compute explicitly nonradiative recombination via bulk states as well as surface recombination at each bias and trap occupancy level for each time increment of the simulation.…”

“…All energies, E c , E v , and E f , are functions of position in the semiconductor. 33,45,51,[57][58][59] Equation 5 thus indicates that holes can transfer to redox donors in the solution with a rate constant k ht and to filled trap states at the surface with a rate constant k p,s . Equation 6 is the analogous expression for electrons.…”