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.
We have observed the prompt emission of GRB 100418A from its beginning by the MAXI/SSC (0.7-7 keV) on board the International Space Station followed by the Swift/XRT (0.3-10 keV) observation. The light curve can be fitted by a combination of a power law component and an exponential component (decay constant is 31.6 ± 1.6 sec).
The spectral and the time dependent piezoelectric photoacoustic (PPA) measurements under the continuous light illumination were carried out at 85 K to investigate nonradiative recombination processes involving EL2 defect levels in carbon doped semi-insulating (SI) GaAs. The decrease of the PPA signal due to the photoquenching effect of EL2 was observed for a short period of illumination of 1.12 eV. It was found that the photoquenching becomes drastic with increasing the carbon concentration. After fully photoquenching, the PPA signal increased again through a local minimum by the continuous light illumination and finally exceeded the initial value before illumination until the saturation level was reached. The deep donor level EL6 and its metastable state are proposed. EL6 level donates electrons to compensate a part of carbon acceptors after photoquenching. The nonradiative recombination through this level generates the PPA signal. The usefulness of the PPA technique for studying the nonradiative transition through deep levels in semiconductor is suggested.
G reat East Japan earthquake of magnitude 9.0 and tsunami in 11 th March, 2011 destroyed Fukushima first nuclear power plant and it brought serious shortage of electrical power in the service area of Tokyo electrical power company (TEPCO).TEPCO carried out the scheduled outage due to this power crisis from 14 th March to 28 th April. However, the scheduled outage will be carried out if we do not save electrical power in summer.This paper shows the countermeasures against scheduled blackout and total power revolution (TPR) which is NTT's saving energy projects including visualization using ICT.
The piezoelectric photoacoustic (PPA) measurements before and after the secondary light illumination for 3 minutes were carried out at 85 K to investigate the electron and hole photoionization processes of EL2 in carbon concentration controlled semi-insulating (SI) GaAs. The result showed a broad peak around 1.0 eV and a hump up to the band gap energy. These were due to hole and electron photoionization processes of EL2, respectively, and these processes were clearly observed from a nonradiative recombination point of view for the first time. In addition, we found that the hole photoionization process of EL2 is not influenced by the secondary light illumination at low temperature. Although the electron photoionization underwent photoquenching effect upon an illumination of 1.12 eV, the hole photoionization process did not change even after a long period of illumination. The positively charged EL2 donor state may not transform to the metastable state.
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