Two nondestructive techniques of surface photovoltage (SPV) and piezoelectric photothermal (PPT) spectroscopies were adopted to investigate GaAs/AlAs multiple quantum well (MQW) heterostructures fabricated on a GaAs substrate, which is difficult to obtain the absorption spectra using a conventional technique. Excitonic and two-dimensional step-like subband absorptions corresponding to the density of states of MQW were obtained by subtracting the background signal from the substrate signal at room temperature. We also conclude that a difference between SPV and PPT spectra indicates the nonradiative component of the carrier relaxation processes in MQW. We found that the combination of SPV and PPT measurements is a powerful method of investigating the carrier confinement and recombination processes in MQW.
Articles you may be interested inBroadening effects and ergodicity in deep level photothermal spectroscopy of defect states in semi-insulating GaAs: A combined temperature-, pulse-rate-, and time-domain study of defect state kinetics Investigation of the annealing effect on the nonradiative carrier recombination in AlGaAs/GaAs utilizing the piezoelectric photothermal technique Rev. Sci. Instrum. 74, 550 (2003); 10.1063/1.1515888
Field-enhanced trapping in deep levels by multiple phonon emission in semi-insulating GaAsThe temperature variation of the piezoelectric photo-thermal ͑PPT͒ signal intensity of semi-insulating ͑SI͒ GaAs from 20 to 150 K was measured. Four peaks at 50, 70, 110, and 125 K were observed in the PPT signal. From the theoretical analysis based on the rate equations of electrons in the conduction band and deep levels, we concluded that the observed four peaks were due to the nonradiative electron transitions through EL6, EL7, EL15, and an unspecified deep level, respectively. Deep levels with extremely low concentration (10 12 -10 15 cm Ϫ3 ) were clearly identified in SI GaAs by using the PPT method.
Investigation of the annealing effect on the nonradiative carrier recombination in AlGaAs/GaAs utilizing the piezoelectric photothermal technique Rev. Sci. Instrum. 74, 550 (2003); 10.1063/1.1515888Lattice relaxation and metastability of the EL2 defect in semi-insulating GaAs and low temperature GaAsThe spectral and the time dependent piezoelectric photoacoustic ͑PPA͒ measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon concentration controlled and not intentionally doped semi-insulating ͑SI͒ GaAs. The decrease of the PPA signal due to the photoquenching effect of EL2 is observed for a short period of illumination in the photon energy region from 1.0 to 1.3 eV. Since almost all of the carbon acceptors are compensated by deep donor EL2 in SI GaAs, electron occupancy of EL2 level can be controlled by changing the carbon acceptor concentration. It is found that the photoquenching becomes drastic with increasing the carbon concentration. After fully photoquenching, the PPA signal increases again through a local minimum by the continuous light illumination and finally exceeds the initial value before illumination until the saturation level is reached. The deep donor level EL6 and its metastable state are proposed. EL6 level donates electrons to compensate a part of carbon acceptors after EL2 0 to EL2* transition is accomplished. The nonradiative recombination through this level generates the PPA signal. Since the PPA measurement can detect lower concentration of EL6 than that of EL2, the higher sensitivity of the PPA measurements than the optical absorption measurements is pointed out. The usefulness of the PPA technique for studying the nonradiative transition through deep levels in semiconductors is also suggested.
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