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준원자층 적층 방법으로 형성된 2형 양자점의 광 발광 특성 연구
김종수,조현준,소모근,김종수,김영호,이상준,이승현,Christiana B. Honsberg,김희대 한국물리학회 2019 새물리 Vol.69 No.8
We have studied the optical properties of InAs/GaAsSb submonolayer quantum dots (SML-QDs) through excitation intensity (Iex) and temperature dependent photoluminescence (PL) experiments. The SML-QDs with type-I (T-1) and type-II (T-2) band structures were grown using a GaAsSb spacer with a Sb composition of 0% and 15.8%. At 13 K, the PL signals from the T-1 and the T-2 samples were observed at 1.42 eV and 1.37 eV, respectively, when the Iex was 8.7 mW/cm2. The PL signal of the T-1 sample is due to the recombination of electrons and holes in the InAs SML-QDs. The PL signal of the T-2 sample is due to the recombination of electrons (in the GaAs electron band) and holes (in the GaAsSb spacer hole band) by type-II band alignment formed between GaAs and GaAsSb. The full widths at half maxima (FWHMs) of the T-1 and the T-2 samples were 7.09 meV and 24.6 meV, respectively, because the T-2 sample has a lower uniformity than the T-1 sample. As the excitation intensity was increased, the PL signals of the T-1 and the T-2 samples shifted to lower energy because of the quantum-confined Stark effect. As a result of these temperature-dependent PL experiments, the activation energy of the T-1 sample was found to be 30 meV. InAs/GaAsSb submonolayer 양자점(SML-QD)의 광학적인 특성을 여기광 세기(Iex)와 온도에 따른광발광 (Photoluminescence; PL) 실험을 통하여 연구하였다. 본 연구에 사용된 시료는 간격자인 GaAsSb 층의 Sb조성을 0%와 15.8%로 조절하여 Type-I (T-1) 과 Type-II (T-2) 밴드 구조의 SML-QD를 성장하였다. 13 K에서 Iex 가 8.3 mW/cm2 일 때 T-1과 T-2 시료의 PL신호는 각각 1.419 eV와 1.368 eV 에서 관측되었다. T-1 시료에서 관측된 전이신호는 InAs SML-QD의 전자와 정공간의 재결합에 의한것이다. T-2시료에서 관측된 PL신호는 GaAs와 GaAsSb 사이에 형성된 type-II 밴드 정렬에 의하여GaAs 전도대의 전자와 GaAsSb 간격자의 가전자대의 정공간의 재결합에 의한 것이다. 두 신호의 반값온폭 (Full-width at half maximum; FWHM)은 각각 7.09 meV와 24.6 meV 이었으며, 이는 T-2시료가T-1시료보다 균일성이 낮기 때문으로 사료된다. 여기광의 세기가 증가할수록 T-1와 T-2시료의 PL신호는낮은 에너지 쪽으로 이동하였는데, 이는 구속된 운반자에 의한 양자 구속 스타크 효과(quantum-confined Stark effect) 에 의한 것으로 사료된다. 온도 의존성 PL 실험의 결과, T-1 시료의 SML-QD의 활성화에너지는 30 meV이었다.
Detection of the third transition of InAs/GaAsSb quantum dots
김영호,Keun-Yong Ban,Som N. Dahal,Heather McFelea,Christiana B. Honsberg 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.4
The optical properties of InAs quantum dots (QDs) embedded in GaAs0.92Sb0.08 barriers have been studied. The samplesstudied consist of 20 multiple layers of InAs QDs embedded in GaAs0.92Sb0.08, with each QD/barrier system separated by a 100nm GaAs spacer. No appreciable changes in the QD properties, such as size, shape, and density, are observed by ScanningTransmission Electron Microscopy (STEM) images. The δ-doping plane beneath the InAs QDs allows the occupancy of theQD electronic sub-band states to be controlled. Low temperature (77 K) Fourier Transformation-Infrared Spectroscopy (FTIR)results, using a multiple internal reflection (MIR) technique to enhance the optical path length, show intersubbandabsorption in the InAs QD area. The broad peak observed around 240 meV corresponds to the energy separation between theelectron ground state and the continuum state of the QDs. Another broad peak around 440 meV is ascribed to a transitionbetween a deep level and shallow donor level due to δ-doping as the signal increases as the doping density increases. Bandstructure calculations using an eight band k·p method are used to confirm the experimental results observed here.
김민석,조현준,김영호,Seung Hyun Lee,이상준,Christiana B. Honsberg,김종수 한국진공학회 2018 Applied Science and Convergence Technology Vol.27 No.5
Optical properties of InAs/GaAs submonolayer-quantum dot (SML-QD) have been investigated using excitation intensity (Iex)- and temperature-dependent photoluminescence (PL). At a low temperature (13 K) strong PL was observed at 1.420 eV with a very narrow full-width at half maximum, of 7.09 meV. The results of the Iex dependence show that the PL intensities increase with increasing Iex. The enhancement factors (k) of PL increment as a function of Iex are 3.3 and 1.22 at low and high Iex regime, respectively. The high k value at low Iex, implies that the activation energy of the SML-QDs is low. The calculated activation energy of the SML-QDs from temperature dependence is 30 meV
Ban, Keun-Yong,Kim, Yeongho,Kuciauskas, Darius,Bremner, Stephen P,Honsberg, Christiana B Institute of Physics 2016 Semiconductor science and technology Vol.31 No.12
<P>The optical properties of InAs quantum dots (QDs) embedded in a GaAsSb matrix with different delta (<I>δ</I>)-doping levels of 0, 2, 4, and 6 electrons per dot (e<SUP>−</SUP>/dot), incorporated to control the occupation of QD electronic states, are studied by photoluminescence (PL) spectroscopy. The time-resolved PL data taken at 10 K reveal that the increase of <I>δ</I>-doping density from 2 to 6 e<SUP>−</SUP>/dot decreases the recombination lifetime of carriers at ground states of the QDs from 996?±?36 to 792?±?19 ps, respectively. Furthermore, the carrier lifetime of the sample with 4 e<SUP>−</SUP>/dot is found to increase at a slower rate than that of the undoped sample as temperature increases above 70 K. An Arrhenius plot of the temperature dependent PL intensity indicates that the thermal activation energy of electrons in the QDs, required for carrier escape from the dot ground state to continuum state, is increased when the <I>δ</I>-doping density is high enough (>4 e<SUP>−</SUP>/dot). These results are attributed to the enhanced Coulomb interaction of electrons provided by the <I>δ</I>-doping, leading to reduced thermal quenching of the PL.</P>
On Electroless Plating and Double Sided Buried Contact Silicon Solar Cells
Ebong, A.U.,Kim, D.S.,Lee, S.H.,Honsberg, C.B. Materials Research Society of Korea 1996 한국재료학회지 Vol.6 No.6
The double sided buried contact(DSBC)silicon solar cell processing requires doping of the rear and front grooves with boron and phosphorus respectively. The successful electroless plating of these grooves with the appropriate metals haave been found to depend on the boron conditions for the rear fingers. However, an increased understanding of electroless plating has removed this restriction. Thus the DSBC cells using different boron conditions can be electrolessly plated with ease. This paper presents the recent work done on metallizing the double sided buried contact silicon solar cells with heavily doped boron grooves. The cells results indicate that, the heavier the boron grooves, the poorer the cell performance because of the probable higher metal contact recombination associated with boron grooves.
Temperature dependence of GaSb and AlGaSb solar cells
Ehsan Vadiee,Yi Fang,Chaomin Zhang,Alec M. Fischer,Joshua J. Williams,Emma J. Renteria,Ganesh Balakrishnan,Christiana B. Honsberg 한국물리학회 2018 Current Applied Physics Vol.18 No.6
Sb-based alloys offer great potential for photovoltaic and thermophotovoltaic applications. In this paper, we study the performance of AlxGa1-xSb (x=0, 0.15, and 0.50) single-junction solar cells over a temperature range of 25–250 °C. The dark current-voltage, one-sun current-voltage, and external quantum efficiency measurements were acquired at different temperatures. Correlations between experimental and numerical results are made to draw conclusions about the thermal behavior of the cells. It is shown that, while the bandgaps decrease linearly with temperature leading to the reduction of open-circuit voltages, the short-circuit current densities decrease with non-linear trends. The temperature-dependent dark current densities were extracted by fitting the dark current-voltage curves to single- and double-diode models to give an insight into the effect of intrinsic carrier concentration (ni) on the cell performance. We find that the ni has a significant impact on temperature-dependent cell performance. These findings could lay a groundwork for the future Sb-based photovoltaic systems that operate at high temperatures.
Kim, Minseak,Jo, Hyun Jun,Kim, Yeongho,Lee, Seung Hyun,Lee, Sang Jun,Honsberg, Christiana B.,Kim, Jong Su The Korean Vacuum Society 2018 Applied Science and Convergence Technology Vol.27 No.5
Optical properties of InAs/GaAs submonolayer-quantum dot (SML-QD) have been investigated using excitation intensity ($I_{ex}$)- and temperature-dependent photoluminescence (PL). At a low temperature (13 K) strong PL was observed at 1.420 eV with a very narrow full-width at half maximum, of 7.09 meV. The results of the $I_{ex}$ dependence show that the PL intensities increase with increasing $I_{ex}$. The enhancement factors (k) of PL increment as a function of $I_{ex}$ are 3.3 and 1.22 at low and high $I_{ex}$ regime, respectively. The high k value at low $I_{ex}$, implies that the activation energy of the SML-QDs is low. The calculated activation energy of the SML-QDs from temperature dependence is 30 meV.