광전류 분광법에 의한 InAs/GaAs 양자점의 특성 연구

조현준,김정화,배인호,김인수 한국물리학회 2010 새물리 Vol.60 No.2

The properties of InAs/GaAs quantum dots grown by using molecular beam epitaxy(MBE) were investigated. The current-voltage (I-V) curves for probe beams with various energies showed that electron-hole pairs excited in quantum dots directly contributed to the conduction current. The two-photon absorption in the quantum dot was observed in the I-V curve at 18 K. With increasing temperature from 18 to 120 K, the conduction current increased due to rising carrier escape from the quantum dots, but decreased at temperature above 150 K due to increasing thermal resistance. Photocurrent spectroscopy allowed the origins of the quantum dot signals to be determined and showed a charge in the direction of the current with increasing temperature. 불순물이 첨가되지 않은 GaAs(100) 기판 위에 molecular beam epitaxy(MBE)법으로 성장시킨 InAs/GaAs 양자점 구조의 광전류 특성을 연구하였다. 입사광의 에너지를 변화시키면서 전류-전압(I-V)을 측정한 결과 양자점에서 여기된 전자-정공 쌍이 전도전류에 직접적으로 기여함을 알 수 있었다. 온도 18 K에서 측정된 I-V 곡선을 통하여 양자점에서 두 광자 흡수 현상을 확인하였다. 18 K에서 120 K까지 온도가 증가함에 따라 양자점에서 운반자(carrier) 탈출이 증가하여 전도전류가 점차 증가하였으며, 온도 150 K 이상에서는 열에너지에 의한 시료의 저항 증가로 다시 감소하였다. 광전류 분광법을 통하여 1.244와 1.352 eV에서 양자점 신호를 관측하였다. 그리고 온도가 증가함에 따라 120 K 이상에서 내부 전류의 방향이 변경되는 것을 확인하였다.

InAs/GaAs 양자점 태양전지의 접합 전기장의 감소에 대한 원인 규명

한임식,김종수,노삼규,이상준 한국물리학회 2017 새물리 Vol.67 No.4

본 연구에서는 InAs/GaAs 양자점 태양전지의 접합 전기장의 감소에 대한 원인을 규명하기 위해 광반사변조분광학 (photoreflectance spectroscopy, PR)을 이용하여 연구하였다. 여기광 세기에 따른 태양전지의 PR 신호를 상온에서 측정한 결과로부터, 시료 내부의 p-n 접합 전기장 ($F_{pn}$)에 의한 Franz-Keldysh oscillation (FKO) 신호를 관측하였다. 저강도의 여기광에서 GaAs 단일 접합과 InAs/GaAs 양자점 태양전지의 $F_{pn}$의 변화 ($\Delta F_{pn}$)는 약 34 kV/cm이다. 이는 n-GaAs 흡수층의 운반자 밀도가 감소된 것으로 사료된다. 운반자 밀도 손실에 따른 양자점 태양전지의 p-n 접합을 이룬 경계면에서 발생되는 최대 전기장 세기의 변화 ($\Delta F_{max}$)를 계산하여 비교 및 분석하였다. 양자점 태양전지의 운반자 밀도 손실이 약 28% 증가하였을 때, 계산된 $\Delta F_{max}$와 PR 실험을 측정된 $\Delta F_{pn}$의 결과가 일치함을 나타내었다. 이는 InAs 양자점 성장에서 발생되는 결함으로 인한 운반자 트랩과 양자화된 준위에서 발생되는 운반자 포획 또는 재-포획 과정으로 인해 운반자 밀도가 손실되어 전기장의 세기가 감소된 것으로 사료된다. We investigated the origin of the reduction in the junction electric field of an InAs/GaAs quantum-dot solar cell (QDSC) by using photoreflectance (PR) spectroscopy. From the PR results with various excitation intensities ($I_{ex}$), the PR spectra clearly exhibited an oscillatory feature related to Franz-Keldysh oscillations (FKOs) due to the p-n junction electric field ($F_{pn}$). The strength of the $F_{pn}$ in the InAs/GaAs QDSC with various $I_{ex}$ was lower than that of the GaAs single-junction SC. The difference in the $F_{pn}$ ($\Delta F_{pn}$) between the GaAs single-junction solar cell and the InAs/GaAs QD solar cell with low $I_{ex}$ is about 34 kV/cm. This result can be explained by a decrease in the carrier concentration ($N_d$) in the n-GaAs absorption layer. To confirm the reduction of $N_d$ in the QDSC, we calculated the variation in the maximum electric field ($\Delta F_{max}$) in a p-n junction with various carrier concentration losses. When the carrier concentration loss in the QDSC was increased by 28%, the calculated $\Delta F_{max}$ coincided exactly with measured $\Delta F_{pn}$ from the PR results. The decreased $N_d$ in the InAs/GaAs QDSC is attributed to a decrease in the electric field strength due to the carrier trapping and re-capturing processes in the defect and QD states.

Temperature- and Excitation-power-dependent Optical Properties of InAs/GaAs Quantum Dots by Comparison of Photoluminescence and Photoreflectance Spectroscopy

김종수,ByoungSoo Ko,Jae-In Yu,배인호 한국물리학회 2009 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.55 No.2

The optical properties of InAs/GaAs quantum dots (QDs) were investigated by using temperature-dependent and excitation-power-dependent photoreflectance (PR) spectroscopy, and the results were compared with those obtained using photoluminescence (PL) spectroscopy. We succeeded in evaluating the built-in electric field in InAs/GaAs QDs by using a PR experiment with the fast Fourier transform (FFT) method. The built-in electric field in InAs/GaAs QDs was strongly affected by the excitation-power and the sample temperatures. The temperature dependence of the built-in electric field in strained InAs/GaAs QDs may be explained by the temperature dependence of the carrier confinement effect in the InAs/GaAs QDs.

Temperature Dependent Photoluminescence from InAs/GaAs Quantum Dots Grown by Molecular Beam Epitaxy

이경수,오규진,김은규,송진동 한국진공학회 2017 Applied Science and Convergence Technology Vol.26 No.4

We have reported structural and optical properties of self-assembled InAs/GaAs quantum dot (QD) grown by molecular beam epitaxy with different arsenic to indium flux ratios (V/III ratios). By increasing the V/III ratio from 9 to 160, average diameter and height of the InAs QDs decreased, but areal density of them increased. The InAs QDs grown under V/III ratio of 30 had a highest-aspect-ratio of 0.134 among them grown with other conditions. Optical property of the InAs QD was investigated by the temperature-dependent photoluminescence (PL) and integrated PL. From the temperature dependence PL measurements of InAs QDs, the activation energies of Ea1 and Ea2 for the InAs QDs were obtained 48 ± 3 meV and 229 ± 23 meV, respectively. It was considered that the values of Ea1 and Ea2 are corresponded to the energy difference between ground-state and first excited state, and the energy difference between ground-state and wetting layer, respectively.

Photocurrent Spectroscopy of InAs/GaAs Quantum Dots Grown by Using MBE

조현준,배인호 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.5

The electrical properties of InAs/GaAs quantum dots grown by using molecular beam epitaxy (MBE) were studied by using photocurrent (PC) spectroscopy. From the photocurrent spectrum at 20 K, the signals around 1.24 and 1.49 eV were related to the quantum dots and the GaAs layer, respectively. The bias voltage dependence of the PC spectra showed that the Schottky barrier height of Au/GaAs was 0.8 V. In the temperature dependence of I-V curves, the photocurrent intensity changed differently for different incident photon energies (1.3 and 1.6 eV) because of a decrease in the excitons binding energy in the quantum dots.

대기압 MOCVD 시스템을 이용하여 Si 기판 위에 자발적으로 형성된 InAs 양자점에 대한 연구

유충현,Yoo, Choong-Hyun 한국전기전자재료학회 2005 전기전자재료학회논문지 Vol.18 No.6

Fully coherent self-assembled InAs quantum dots(QDs) grown on Si (100) substrates by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) were grown and the effect of growth conditions such as growth rate and growth time on quantum dots' morphology such as densities and sizes was investigated. InAs QDs of 30 - 80 nm in diameters with densities in the range of (0.6 - 1.7) x $10^{10}\;cm^{-2}$ were achieved on Si substrates and InAs layer was changed from 2 dimensional growth to 3 dimensional one at a nominal thickness less than 0.48 ML. This is attributed to the higher ambient pressure of APMOCVD suppressing of In segregation from the 2 dimensional InAs layer. This In segregation looked to disturb the dot formation especially when the growth rate was low so that the dots became less dense and bigger as the growth rate was lower.

InAs/GaAs Self-organized Quantum Dots의 전기.광학적 특성 연구

김기홍,박종도,배인호,손정식,문병연,이주인 한국전기전자재료학회 2001 전기전자재료학회논문지 Vol.14 No.2

We present a detailed of the interband transitions of InAs/GaAs self-organized quantum dots(QDs) based on surface photovoltage(SPV), photoreflactance(PR) and photoluminescence(PL) spectroscopies. At room temperature, interband absorption transitions of QDs have been observed by using SPV spectrum, which clearly exhibits three well-resolved absorption transitions of QDs have been observed by using SPV spectrum, which clearly exhibits three well-resolved absorption peaks. The absorption line shape is Gaussian-like. Furthermore, the corresponding interband transitions are also observed in PR and PL experiments at 77K.

V 홈 바닥에 형성된 일차원 InAs 양자점

손창식,최인훈,박용주,Son, Chang-Sik,Choi, In-Hoon,Park, Young-Ju 한국재료학회 2003 한국재료학회지 Vol.13 No.11

One-dimensional array of InAs quantum dots (QDs) have been grown on V-grooved GaAs substrates by low-pressure metalorganic chemical vapor deposition. Atomic force microscope images show that InAs QDs are aligned in one-dimensional rows along the [011]oriented bottom of V-grooves and no QDs are formed on the sidewalls and the surface of mesa top. Capability to grow one-dimensional InAs QDs array would feasible for the single electron tunneling devices and other novel quantum-confined devices.

Si 기판 위에 형성된 InAs 양자점의 열처리에 의한 표면 상태의 변화

유충현,Yoo, Choong-Hyun 한국전기전자재료학회 2007 전기전자재료학회논문지 Vol.20 No.10

Effect of high-temperature annealing on morphology of fully coherent self-assembled InAs quantum dots' grown on Si (100) substrates at $450^{\circ}C$ by atmospheric pressure metalorganic chemical vapor deposition(APMOCVD) was investigated by atomic force microscopy(AFM). When the dots were annealed at 500 - 600$^{\circ}C$ for 15 sec - 60 min, there was no appreciable change in the dot density but the heights of the dots increased along with the reduction in the diameters. In segregation from the InAs quantum dots and/or from the 2-dimensional InAs wetting layer which was not transformed into quantum dots looked responsible for this change in the dot size. However the change rates remained almost same regardless of annealing time and temperature, which may indicate that the morphological change due to thermal annealing is done instantly when the dots are exposed to high temperature annealing.

MBE법으로 성장한 InAs 양자점의 Photoluminescence 특성

김근형 ( Geun Hyeong Kim ),김기홍 ( Ki Hong Kim ) 대구가톨릭대학교 자연과학연구소 2013 자연과학연구논문집 Vol.11 No.1

The optical characterization of self-assembled InAs/GaAs quantum dots(QD) grown by MBE were investigated using photoluminescence(PL). The results of the InAs/GaAs single layer quantum dots without buffer layer (S1) and with 500 nm buffer layer (S2) are as follows. From the PL spectra at temperature 26K, the peak energy and FWHM originated from QDs of the samples with buffer layer are higher and sharper than that without buffer layer. This results indicate that the effect of buffer layer make small size and smaller size distribution of InAs QDs in the growth process.