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Electrical Properties of Digital-Alloy (AlxGa1-x)As/GaAs During Molecular Beam Epitaxy Growth
Jin Soak Kim,김은규,송진동,Jung Il Lee 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.50 No.6
We have investigated the electrical properties of digital-alloy AlGaAs on GaAs by using capacitance-voltage (C-V) and deep-level transient spectroscopy (DLTS) methods. During molecular beam epitaxy growth, digital-alloy and analogue-alloy samples were prepared. The digital-alloy layer consists of hundreds of AlAs and GaAs layers each thickness of 2 monolayers. Most properties of the digital alloy were similar to the analogue alloy, but some electrical properties from these of digital-alloy were quite different to the analogue-alloy from the C-V and low-temperature DLTS measurements. Especially, the superlattice structures slightly interrupt carrier motion at low temperatures ($<$80 K); then, a signal whose origin seems to be a hetero barrier of the GaAs/AlGaAs quantum well is found, and its average activation energy is estimated to be about 45 meV.
Kim, Jin Soak,Kim, Eun Kyu,Han, Il Ki,Song, Jin Dong,Lee, Jung Il,Lee, Sejoon,Shon, Yoon,Kim, D Y Institute of Physics 2006 Semiconductor science and technology Vol.21 No.8
<P>We have investigated the defect states and confined energy levels of three quantum wells (QWs) in the quantum cascade laser (QCL) structure by capacitance–voltage and deep-level transient spectroscopy methods. Defect states with activation energies in the range of 0.49–0.88 eV were obtained in the GaAs capping layer, and their origins were considered as EL3 and EL2 families, which are well-known deep levels of GaAs materials. The densities of these defects in the GaAs capping layer of the QCL structure were about 3–12% of the donor concentration. The confined energy levels of QWs showed activation energies of about 130 meV and 230 meV from the top of the AlGaAs barrier, and their carrier confinement ability was measured to be about 0.5% of the donor concentration.</P>
Kim, Jin Soak,Kim, Eun Kyu,Kim, Jun Oh,Lee, Sang Jun,Noh, Sam Kyu WILEY-VCH Verlag 2009 Physica Status Solidi. B Vol.246 No.4
<P>Energy levels of InAs/GaAs self-assembled quantum dot (QD) system were analyzed by capacitance–voltage (C –V) and deep level transient spectroscopy (DLTS) methods. The QD signals were partially separated by DLTS measurement with small bias changing. The activation energies of QD signals were varied from 66 meV to 610 meV by changing of 0.6 V applied bias, which energies are related to the confined energy levels of InAs QDs. Then, the ground states of InAs QDs were considered to be located at 0.61 eV below the conduction band edge of GaAs barrier. In addition, it showed that DLTS signal of QDs are largely affected by their density of energy state. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Study on the Energy-Band Structure of Indium-Rich InGaN/GaN Quantum Dot System
Jin Soak Kim,김은규,윤의준,Hee Jin Kim 한국물리학회 2007 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.51 No.3
The ground-state energy levels and energy band structures of the In-rich InGaN/GaN quantumdot (QD) system were analyzed by performing the capacitance-voltage (C-V), deep-level transient spectroscopy (DLTS), and photoluminescence (PL) measurements. The InGaN QD system was grown by using a metal-organic chemical vapor deposition method. The lateral size, the height, and the density of a disc-shaped InGaN QDs were 47.3 nm, 1.2 nm and 9.0 × 109 cm.2, respectively. The ground states of the InGaN QDs were located at 0.44 eV from the top of the barrier, which correspond to the conduction band edge of GaN. The QDs had various levels, except for the ground-state energy. A band-to-band transition energy of 2.92 eV was found by using PL measurements. Moreover, antisite point defects were also founded in GaN buffer layer, and their activation energy and emission cross-section were 0.70 eV and 1.19 × 10.13 cm2, respectively.
Kim, Young-Soak,Jin, Sung-Ha The Pharmaceutical Society of Korea 2004 Archives of Pharmacal Research Vol.27 No.8
In human neuroblastoma SK-N-BE(2) cells undergoing apoptotic death induced by ginsenos-ide Rh2, a dammarane glycoside that was isolated from Panax ginseng C. A. Meyer, caspase-1 and caspase-3 were activated. The expression of Bax was increased in the cells treated with ginsenoside Rh2, whereas Bcl-2 expression was not altered. Treatment with caspase-1 inhibi-tor, Ac-YVAD-CMK, or caspase-3 inhibitor, Z-DEVD-FMK, partially inhibited ginsenoside Rh2-induced cell death but almost suppressed the cleavage of the 116 kDa PARP into a 85 kDa fragment. When the levels of p53 were examined in this process, p53 accumulated rapidly in the cells treated early with ginsenoside Rh2. These results suggest that activation of caspase-1 and -3 and the up-regulation of Bax are required in order for apoptotic death of SK-N-BE(2) cells to be induced by ginsenoside Rh2, and p53 plays an important role in the pathways to promote apoptosis.
Song, Hooyoung,Kim, Jin Soak,Kim, Eun Kyu,Seo, Yong Gon,Hwang, Sung-Min IOP Pub 2010 Nanotechnology Vol.21 No.13
<P>The potential of nonpolar <I>a</I>-plane InGaN/GaN multi-quantum wells (MQWs), which are free from a strong piezoelectric field, was demonstrated. An <I>a</I>-GaN template grown on an <I>r</I>-plane sapphire substrate by the multi-buffer layer technique showed high structural quality with an omega full width at half maximum value along the <I>c</I>-axis of 418 arcsec obtained from high-resolution x-ray diffraction analysis. From barrier analysis by deep level transient spectroscopy, it appeared that <I>a</I>-plane InGaN/GaN MQWs can solve the efficiency droop problem as they have a lower electron capture barrier than the <I>c</I>-plane sample. The peak shift of the temperature-dependent photoluminescence signal for the nonpolar InGaN/GaN MQWs was well fitted by Varshni’s empirical equation with zero-internal fields. A high photoluminescence efficiency of 0.27 from this sample also showed that nonpolar MQWs can be the key factor to solve the efficiency limitation in conventional <I>c</I>-plane GaN based light emitting diodes. </P>