Photoluminescence lifetime in heterojunctions

Room-temperature photoluminescence decay time measurements in heavily doped GaAs:C-layers designed as base layers for heterojunction bipolar transistors are reported. These measurements provide access to nonequilibrium minority carrier lifetimes that determine the current gains of those devices. By systematically studying transient luminescence spectra over a wide range of excitation densities between 10 13 and 10 18 cm Ϫ3 , we demonstrate the importance of carrier trapping processes at low excitation densities. Optimized excitation conditions that achieve trap saturation but also avoid stimulated emission are found for densities of (1-3)ϫ10 17 cm Ϫ3 /pulse. Detection is limited to a spectral window well above the energy gap ͑beyond 1.5 eV͒. Values for both Auger and radiative recombination coefficients are given.

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“…Within the model introduced in Ref. 18 the layer thickness dependence of the PL decay times is given by…”

Section: Nonequilibrium Carrier Lifetimesmentioning

confidence: 99%

Minority-carrier kinetics in heavily doped GaAs:C studied by transient photoluminescence

Maaßdorf

Grämlich

Richter

et al. 2002

Journal of Applied Physics

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“…Although there are many papers about this method, there is up to now no universal analytical solution (including all important influences: high-injection effects, space charge field and band bending, generation attributed to selfabsorption-photon recycling) for the calculation of the PL decay in the nanosecond range, in spite of the different models proposed. [3][4][5][6][7][8][9][10][11][12][13][14] To solve the problems concerning the quantitative interpretation of the experimental results obtained for the PL decay of semiconductor electrodes under different experimental conditions, several approximations, simplifications, and assumptions were made:…”

Section: (I) Introductionmentioning

confidence: 99%

“…(2) The influence of the space charge field on the carrier dynamics was neglected in the time-dependent (diffusion) model by either implicitly assuming the flat band case3-7•9•12•16 or assuming the excess minority carrier density is zero at the inner edge of the depletion region. 10 The flat band case was realized experimentally by an externally applied potential13•14 or by the high injection limit.8 •11•15 (3) The rate of the bulk recombination r is assumed to be linear in p, generally expressed by r = / in the continuity equation for the minority carrier concentration.7 (4) The surface recombination velocity S, characterizing the process of nonradiative surface recombination, is usually considered to be independent of the injection density and is incorporated in the model as a constant in the boundary condition of the continuity equation.…”

Section: (I) Introductionmentioning

confidence: 99%

“…The carrier distribution was chosen as uniform in the ydimension. G(t) denotes the Gaussian time function G(t) = Q exp ((-u 2iH (10) Corresponding to our experimental arrangement described previously,18 we chose the half-width time fa = 0.5 ns and tm" = 2 ns in each case. It should be noted that the excitation function used throughout both parts of this paper was not a ó function.…”

Section: (I) Introductionmentioning

confidence: 99%

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

Krueger¹,

Jung²,

Gajewski³

1994

J. Phys. Chem.

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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.

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“…Thus in the linear model: (4) As the material quality improved, observations were made suggesting that Eq. 4 was violated for certain devices and: Equation 5 can be explained by the self-absorption of radiation and the phenomena of photon recycling.…”

Section: Minority-carrier Parameter Characterizationmentioning

confidence: 99%

Design of high efficiency solar cells by photoluminescence studies

Ahrenkiel

Dunlavy

Keyes

et al.

IEEE Conference on Photovoltaic Specialists

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A metal-organic chemical vapor deposition (MOCVD) AI,Gal -,As passivated GaAs single junction solar cell with AM1.5 efficiency of 24.8% was recently reported. Growth process research was greatly expedited by complementary time-resolved photoluminescence measurements on double heterostructures. The latter simulated the active regions of the solar cell and produced values of the minority carrier lifetime and interface recombination velocity of the components of the solar cell. Photon recycling was shown to be a significant process in the effective lifetime of the various structures.Interface recombination was found to limit the lifetime in materials grown at temperatures below 740°C.

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Photoluminescence lifetime in heterojunctions

Cited by 37 publications

References 9 publications

Minority-carrier kinetics in heavily doped GaAs:C studied by transient photoluminescence

Minority-carrier kinetics in heavily doped GaAs:C studied by transient photoluminescence

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

Design of high efficiency solar cells by photoluminescence studies

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