Transient photocurrents induced by short light pulses at lattice-matched multiplequantum well(MQW)GaAs/Al_(0.3)Ga_(0.7)As electredes were studied in the 1 ×10 ̄(-2)mol·dm ̄(-3)ferrocene([Fc ̄0]/[Fc) ̄+]=9/1)-0.1 mol·dm ̄(-3)tetrabutylammonium tetrafluoroborate acetonitrile solutionin order to examine the relaxation photoprocesses and to evaluate kinetic parameters of superlattice electrodes. GaAs/Al_(0.3)Ca_(0. 7)As MQW electrode consisting of 10 periods with each of GaAs well(5.3nm)and Al_(0. 3)Ga_(0. 7)As barrier(10nm)showed two pronounced and well-resolved peak structures located at 1.503 eV and 1.699 eV in the photocurrent spectrum,corresponding to the theoretical allowedexcitonic transitions(Δn=0) for heavy holes(H11,H22)in the quantum well respectively. Transient photocurrent spectra were measured by a monochromatic light pulse with 7 μs pulsewidth and 9 nJ·cm ̄(-2) of energy at λ=800 nm preduced by a pulsed xenon lamp via amonochromator,and analyzed by Pade boplace transform method. Photocurrent transients werecharacterized by a rapid decays following by a slow exponent at the electrode potential varying from-2.3 V to 0 V vs SCE,and exhibited typical I-V behaviours of n-type semiconductor.Dualexponential transient photocurrent decay were demonstrated by the two segments with different slope inthe relations of normalized logarithm of photocurrent response and decay time, representing twoprocesses-RC(fast)and surface recombination(slow).By fitting the transient decay to the dualexponent function of the form:I(t)=A_1exp(-t/τ_2)+A_2exp(-t/τ_2),where t is the decay time,A_1,A_2 and τ_1,τ_2 correspond to the amplitudes and time constants of the fast and slow decaysrespectively。The kinetic parameters such as the normalized steady state photocurrent(I_s/G_0 )andsurface state lifetime(T_s) were determined in frequency domain. Both of the I_s/G_0 defined as therelative ratio of photogenerated carrier transferred from the electrode to electrolyte and the T_s reflectedthe rate of the surface recombination increased with the positive shifts of electrode potential, due tofast separation of photogenerated electron-hole pairs and slow surface recombination resulted by thelarger band bending created at more positive potential. Comparison with GaAs electrede,significantlylarger I_s/G_0 were obtained in the potential range of-2.3 V to 0 V vs SCE,and longer T_s at morenegative electrode potential for MQW electrede,indicating that the longer lifetime of exciton presentedin the MQW electrede leads to less bulk and surface recombination and higher concentration ofphotogenerated carriers at the interface. The increase of light to electric conversion efficiencies is,therefore,reasonably available in the MOwelectrede systems.


Superlattice(quantum well), Multiple quantum well, Transient photocurrent

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