Annealing effect on the nonradiative carrier recombination in AlGaAs/GaAs investigated by a piezoelectric photothermal s
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Annealing effect on the nonradiative carrier recombination in AlGaAs/GaAs investigated by a piezoelectric photothermal spectroscopy Atsuhiko Fukuyama, Hiroaki Nagatomo, Yoshito Akashi, and Tetsuo Ikari Faculty of Engineering, Miyazaki University, 1-1 Gakuen-kibanadai-nishi, Miyazaki 889-2192, Japan ABSTRACT Electron non-radiative recombination process of photoexcited carriers in as-grown and annealed n-Al0.2 Ga0.8 As/GaAs hetero-structure samples are investigated by using a piezoelectric photothermal spectroscopy (PPTS). The PPT signal above the band-gap energy of GaAs substrate decreased when the sample was annealed at 815◦ C. In the frequency dependent measurements, the deviations from 1/f linear function are clearly observed in the AlGaAs/GaAs samples. This critical deviation frequency was found to shift to the lower frequency region by annealing. Our experimental results are explained by assuming that the sample annealing generates an unknown deep level in AlGaAs epitaxial layer region and this level effectively traps the photoexcited carriers non-radiatively. INTRODUCTION Pseudo-binary compound semiconductor AlGaAs is widely used for quantum electronic devices such as the light emitting diodes (LED) and the hetero bipolar transistor (HBT). Intrinsic deep defect levels in this material are known to cause a degradation of such devices. They trap the free carriers, and thus high frequency operation of electronic devices are seriously influenced. Annealing process followed by an ion-implantation is a most important process in the device fabrication. Since this annealing process affects a formation and a destruction of deep defect levels, it is very important to understand an annealing effect on the carrier generation and recombination properties through deep defect levels. The recombination process of photoexcited carriers is commonly investigated by a photoluminescence (PL) method. This is available technique to understand a light emission mechanism such as band to band, band to impurity level, and impurity to impurity levels transitions. However, the recombination processes of carrier through the deep levels is mainly non-radiative recombination. A strong electron lattice interaction affects these carrier transitions. The PL method can detect only a radiative recombination process. Therefore, it becomes important to establish an alternative experimental technique to investigate such transitions. Recently, we have developed the piezoelectric photo-thermal (PPT) spectroscopy that has a higher sensitivity for investigating the thermal and electronic properties of semiconductors than a conventional microphone photoacoustic method [1]. This also gives us an information of nonradiative transitions through deep defect levels. Extensive works for Si, GaAs, and AlGaAs/GaAs samples were carried out [1-3] and a metastable natures for representative deep levels in GaAs such as EL2 and EL6 were clearly resolved. In the present paper, we propose a model to explaining our experimental results for the non-radiative recombination
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