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류미이,Thomas R. Harris,Buguo Wang,Yung Kee Yeo,Michael R. Hogsed,이상조,김종수,John Kouvetakis 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.75 No.8
The temperature (T)-dependent photoluminescence (PL) from Ge1−ySny (y = 4.3%–9.0%) alloys grown on Ge-buffered Si substrates was studied as a function of the Sn content. The PL from Ge1−ySny alloys with high Sn contents (≥7.0%) exhibited the typical characteristics of direct bandgap semiconductors, such as an increase in the PL intensity with decreasing T and a single PL peak corresponding to a transition from the direct bandgap (Γ-valley) to the valence band at all temperatures from 10 to 300 K. For the Ge1−ySny alloys with low Sn contents (≤6.2%), the PL emission peaks corresponding to both the direct bandgap (ED) and the indirect bandgap (EID) PL appeared at most temperatures and as T was increased, the integrated PL intensities of ED initially increased, then decreased, and finally increased again. The unstrained ED and EID energies estimated from the PL spectra at 75 and 125 K were plotted as functions of the Sn concentration, and the cross-over point for unstrained Ge1−ySny was found to be about 6.4%–6.7% Sn by using linear fits to the data in the range of Sn contents from 0% to 9.0%. Based on the results at 75 and 125 K, the cross-over Sn concentration of unstrained Ge1−ySny should be about 6.4%–6.7% Sn content at room temperature. The ED energies of the Ge0.925Sn0.075 alloys were estimated from the T-dependent photoreflectance spectra, and the ED values was consistent with those obtained from PL spectra.
Temperature-dependent luminescence properties of digital-alloy In(Ga1-zAlz)As
류미이,조일욱,송진동 한국진공학회 2018 Applied Science and Convergence Technology Vol.27 No.3
The optical properties of the digital-alloy (In0.53Ga0.47As)1-z/(In0.52Al0.48As)z grown by molecular beam epitaxy as a function of composition z (z = 0.4, 0.6, and 0.8) have been studied using temperature-dependent photoluminescence (PL) and time-resolved PL (TRPL) spectroscopy. As the composition z increases from 0.4 to 0.8, the PL peak energy of the digital-alloy In(Ga1-zAlz)As is blueshifted, which is explained by the enhanced quantization energy due to the reduced well width. The decrease in the PL intensity and the broaden FWHM with increasing z are interpreted as being due to the increased Al contents in the digital-alloy In(Ga1-zAlz)As because of the intermixing of Ga and Al in interface of InGaAs well and InAlAs barrier. The PL decay time at 10 K decreases with increasing z, which can be explained by the easier carrier escape from InGaAs wells due to the enhanced quantized energies because of the decreased InGaAs well width as z increases. The emission energy and luminescence properties of the digital-alloy (InGaAs)1-z/(InAlAs)z can be controlled by adjusting composition z.
류미이,C.Q. Chen,김진수,M. Asif Khan 한국물리학회 2011 Current Applied Physics Vol.11 No.2
The optical properties of quaternary AlInGaN epilayers and AlInGaN/AlInGaN multiple quantum wells (MQWs) grown by a pulsed metalorganic chemical vapor deposition have been investigated by means of photoluminescence (PL) and time-resolved PL measurements. The PL emission peaks in both AlInGaN epilayers and MQWs show a blueshift with increasing excitation power density. The PL intensities of MQWs are much stronger (∼3―4 times) than that of the epilayer. The PL emission intensities (I_emi) of both AlInGaN epilayers and MQW samples increase superlinearly with increasing excitation power density (I_exc), following a power-law form, I_emi I_exc^β. The PL decay times of MQWs are longer than that of epilayer. The longer PL decay times may be due to a stronger localization effect of carriers/excitons at band tail states and wave function separation caused by the quantum confined Stark effect. These results indicate that AlInGaN/AlInGaN MQWs grown by a PMOCVD are promising materials for ultraviolet light emitting diode (LED) applications similar to the InGaN/InGaN system for blue LED applications.
InAs/GaAs 양자점의 발광특성에 대한 InGaAs 캡층의 영향
권세라,류미이,송진동,Kwon, Se Ra,Ryu, Mee-Yi,Song, Jin Dong 한국진공학회 2012 Applied Science and Convergence Technology Vol.21 No.6
Migration-enhanced molecular beam epitaxy법을 이용하여 GaAs 기판에 성장한 InAs 양자점(quantum dots: QDs)의 광학적 특성을 PL (photoluminescence)과 time-resolved PL을 이용하여 분석하였다. 시료 온도, 여기 광의 세기, 발광 파장에 따른 InAs/GaAs QDs (QD1)과 $In_{0.15}Ga_{0.85}As$ 캡층을 성장한 InAs/GaAs QDs (QD2)의 발광특성을 연구하였다. QD2의 PL 피크는 QD1의 PL 피크보다 장파장에서 나타났으며, 이것은 InGaAs 캡층의 In이 InAs 양자점으로 확산되어 양자점의 크기가 증가한 것으로 설명된다. 10 K에서 측정한 QD1과 QD2의 PL 피크인 1,117 nm와 1,197 nm에서 PL 소멸시간은 각각 1.12 ns와 1.00 ns이고, 발광파장에 따른 PL 소멸시간은 PL 피크 근처에서 거의 일정하게 나타났다. QD2의 PL 소멸시간이 QD1보다 짧은 것은 QD2의 양자점이 커서 파동함수 중첩이 향상되어 캐리어 재결합이 증가한 때문으로 설명된다. The optical properties of InAs quantum dots (QDs) grown on a GaAs substrates by migration enhanced molecular beam epitaxy method have been investigated by using photoluminescence (PL) and time-resolved PL measurements. The luminescence properties of InAs/GaAs QDs have been studied as functions of temperature, excitation laser power, and emission wavelength. The PL peak of InAs QDs capped with $In_{0.15}Ga_{0.85}As$ layer (QD2) measured at 10 K is redshifted about 80 nm compared with that of InAs QDs with no InGaAs layer (QD1). This redshift of QD2 is attributed to the increase in dot size due to the diffusion of In from the InGaAs capping layer. The PL decay times of QD1 and QD2 at 10 K are 1.12 and 1.00 ns taken at the PL peak of 1,117 and 1,197 nm, respectively. The reduced decay time of QD2 can be explained by the improved carrier confinement and enhanced wave function overlap due to increased QD size. The PL decay times for both QD1 and QD2 are independent on the emission wavelength, indicating the uniformity of dot size.
Indium Interruption Growth법으로 성장한 InAs 양자점의 광학적 특성
이희종,류미이,김진수,Lee, Hi-Jong,Ryu, Mee-Yi,Kim, Jin-Soo 한국진공학회 2009 Applied Science and Convergence Technology Vol.18 No.6
분자선 에피택시 (molecular beam epitaxy: MBE)를 이용하여 GaAs (100) 기판에 Indium interruption growth법으로 성장한 InAs 양자점 (quantum dots: QDs)의 광학적 특성을 photoluminescence (PL)와 time-resolved PL (TRPL) 실험을 이용하여 분석하였다. In interruption growth법은 InAs 양자점 성장 동안 As 공급은 계속 유지하면서 셔터 (shutter)를 이용해 서 In 공급을 조절하는 방법이다. 본 연구에서는 In을 1초 동안 공급하고 셔터를 0초, 9초, 19초, 29초, 또는 39초 동안 닫아 In 공급을 차단하였으며, 공급과 차단 과정을 각 30회 반복하여 양자점을 성장하였다. In interruption 시간을 0초에서 19초까지 증가하였을 때 PL 피크는 1096 nm에서 1198 nm로 적색편이 (~100 nm)하고 PL 세기는 증가하였으나, 19초에서 39초까지 증가하였을 때 PL 스펙트럼의 변화는 없고 PL 세기는 감소하였다. 모든 양자점의 PL 소멸시간 (decay time)은 약 1 ns로 바닥상태 (ground state) PL 피크에서 가장 길게 나타났다. In interruption 시간이 19초인 시료가 가장 좋은 PL 특성과 가장 짧은 운반자 소멸시간을 나타내었다. PL 특성의 향상은 In interruption 시간동안 일정한 양의 In 원자들의 분리와 이동이 증가한 것으로 설명될 수 있다. 이러한 결과로부터 In interruption 법을 이용하여 InAs 양자점의 크기, 균일도, 조밀도 등을 조절하여 원하는 파장대의 양자점을 성장할 수 있음을 알 수 있다. We have investigated optical properties of InAs quantum dots (QDs) grown on GaAs (100) substrate by molecular beam epitaxy, by means of photoluminescence (PL) and time-resolved PL spectroscopy. InAs QDs were grown by using In interruption growth technique, in which the In flux was periodically interrupted by a closed In shutter during InAs QDs growth. The shutter of In source was opened for 1 s and then closed for 0, 9, 19, 29, or 39 s. This growth sequence was repeated 30 times during QDs growth. For each sample, the total amount of In contributing to the growth was the same (30 s) but total growth time was varied during the InAs growth. As the In interruption time is increased from 0 to 19 s, the PL peak position of the QDs is red-shifted from 1096 to 1198 nm, and the PL intensity is increased. However, the PL peak is unchanged and the intensity is decreased as the In interruption time is increased further to 39 s. The PL decay times measured at the PL peak position for all the InAs QDs are independent on the QD growth conditions and showed about 1 ns. The red-shift of PL peak and the increase of PL intensity can be explained due to increased QD size and the enhancement in the migration of In atoms using In interruption technique. These results indicated that the size and shape of InAs QDs can be controlled by using In interruption growth technique. Thus the emission wavelength of the InAs QDs on GaAs substrate can also be controlled.
InGaAs/InAlAs 양자우물구조의 발광특성에 대한 In<sub>0.4</sub>Al<sub>0.6</sub>As 버퍼층 성장온도의 영향
김희연,류미이,임주영,신상훈,김수연,송진동,Kim, Hee-Yeon,Ryu, Mee-Yi,Lim, J.Y.,Shin, S.H.,Kim, S.Y.,Song, J.D. 한국진공학회 2011 Applied Science and Convergence Technology Vol.20 No.6
$In_{0.4}Al_{0.6}As$ 버퍼층의 성장온도 변화에 따른 $In_{0.5}Ga_{0.5}As/In_{0.5}Al_{0.5}As$ 다중양자우물(multiple quantum wells, MQWs)의 광학적 특성을 포토루미네션스(photoluminescence, PL)와 시간분해 포토루미네션스(time-resolved PL, TRPL) 측정을 이용하여 분석하였다. $In_{0.4}Al_{0.6}As$ 버퍼층은 기판의 온도를 $320^{\circ}C$에서 $580^{\circ}C$까지 다양하게 변화시키며 $1{\mu}m$ 성장하였으며, 그 위에 $In_{0.5}Al_{0.5}As$ 층을 $480^{\circ}C$에서 $1{\mu}m$ 성장한 후 InGaAs/InAlAs MQWs을 성장하였다. MQWs는 6-nm, 4-nm, 그리고 2.5-nm 두께의 $In_{0.5}Ga_{0.5}As$ 양자우물과 10-nm 두께의 $In_{0.5}Al_{0.5}As$ 장벽으로 이루어졌다. 4-nm QW과 6-nm QW로부터 PL 피크가 나타났으나, $In_{0.4}Al_{0.6}As$ 성장온도 변화가 가장 큰($320^{\circ}C$에서 $580^{\circ}C$까지 변화) 시료는 6-nm QW에서의 PL 피크만 나타났다. 낮은 온도($320^{\circ}C$에서 $480^{\circ}C$까지 변화)에서 성장한 $In_{0.4}Al_{0.6}As$ 버퍼층 위에 성장한 MQWs의 PL 특성이 우수하게 나타났다. 발광파장에 따른 TRPL 결과로 4-nm QW과 6-nm QW에서의 캐리어 소멸시간을 얻었다. The luminescence properties of $In_{0.5}Ga_{0.5}As/In_{0.5}Al_{0.5}As$ multiple quantum wells (MQWs) grown on $In_{0.4}Al_{0.6}As$ buffer layer have been investigated by using photoluminescence (PL) and time-resolved PL measurements. A 1-${\mu}m$-thick $In_{0.4}Al_{0.6}As$ buffer layers were deposited at various temperatures from $320^{\circ}C$ to $580^{\circ}C$ on a 500-nm-thick GaAs layer, and then 1-${\mu}m$-thick $In_{0.5}Al_{0.5}As$ layers were deposited at $480^{\circ}C$, followed by the deposition of the InGaAs/InAlAs MQWs. In order to study the effects of $In_{0.4}Al_{0.6}As$ layer on the optical properties of the MQWs, four different temperature sequences are used for the growth of $In_{0.4}Al_{0.6}As$ buffer layer. The MQWs consist of three $In_{0.5}Al_{0.5}As$ wells with different well thicknesses (2.5-nm, 4.0-nm, and 6.0-nm-thick) and 10-nm-thick $In_{0.5}Al_{0.5}As$ barriers. The PL peaks from 4-nm QW and 6-nm QW were observed. However, for the MQWs on the $In_{0.4}Al_{0.6}As$ layer grown by using the largest growth temperature variation (320-$580^{\circ}C$), the PL spectrum only showed a PL peak from 6-nm QW. The carrier decay times in the 4-nm QW and 6-nm QW were measured from the emission wavelength dependence of PL decay. These results indicated that the growth temperatures of $In_{0.4}Al_{0.6}As$ layer affect the optical properties of the MQWs.
Effect of an InGaP Spacer Layer on the Luminescence Properties of InP/InGaP Quantum Structures
변혜령,류미이,송진동,이창렬 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.5
The optical characteristics of InP/InGaP quantum structures (QSs; quantum dots + quantumdashes) grown by using a migration enhanced epitaxy method have been investigated usingtemperature-dependent photoluminescence (PL) and time-resolved PL (TRPL). An InGaP spacerlayer with different thicknesses (15, 30, and 50 nm) was grown on the InP QSs in order to identifythe effect of the InGaP spacer layer on the luminescence and the carrier dynamics of InP QSs. Asthe thickness of the InGaP layer was increased from 15 to 50 nm, the PL peak exhibited a blueshift,and the PL intensity increased, which are attributed to the increased carrier confinement inthe vertical direction due to the increased height and reduced width and length of QSs. The PLdecay time demonstrated a strong dependence on the emission wavelength and the temperature. Inaddition, the decay time for InP QS samples with InGaP layers of 30 and 50 nm exhibited differentemission-wavelength dependence than that for the InP QS sample with an InGaP layer of 15 nm. These results demonstrate that the optical and the structural properties of InP QSs are significantlyaffected by varying the thickness of the InGaP spacer layer.