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        • KCI등재

          Temperature-Dependent Photoluminescence Studies of Ge1−ySny (y = 4.3%–9.0%) Grown on Ge-Buffered Si: Evidence for a Direct Bandgap Cross-Over Point

          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.

        • KCI등재

          Optical characterization of quaternary AlInGaN epilayer and multiple quantum wells grown by a pulsed metalorganic chemical vapor deposition

          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.

        • KCI우수등재

          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.

        • KCI등재

          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.

        • KCI등재

          As 차단 시간 변화에 의한 InAs 양자점의 광학적 특성

          최윤호,류미이,조병구,김진수,Choi, Yoon Ho,Ryu, Mee-Yi,Jo, Byounggu,Kim, Jin Soo 한국진공학회 2013 Applied Science and Convergence Technology Vol.22 No.2

          Arsenic interruption growth (AIG)법을 이용하여 GaAs 기판에 성장한 InAs 양자점(quantum dots, QDs)의 광학적 특성을 PL (photoluminescence)과 time-resolved PL을 이용하여 분석하였다. AIG법은 InAs 양자점 성장 동안 In 공급은 계속 유지하면서 셔텨(shutter)를 이용해서 As 공급과 차단을 조절하는 방법이다. 본 연구에서는 As 공급과 차단을 1초(S1), 2초(S2), 또는 3초(S3) 동안 반복하여 성장한 InAs QDs과 As 차단 없이 성장한 기준시료(S0)를 사용하였다. AIG법으로 성장한 시료들의 PL 세기는 기준시료보다 모두 강하게 나타나고, As 차단 시간에 따라 PL 피크는 적색이동(redshifted) 또는 청색이동 (blueshifted)하여 나타났다. 기준시료 S0의 PL 피크와 비교하였을 때 S1의 PL 피크의 적색이동은 양자점 평균 길이가 S0보다 증가하였기 때문이며, S3의 청색이동은 양자점 평균 길이가 S0보다 감소하였기 때문이다. AIG법으로 성장한 QDs 시료들의 PL 세기의 증가는 cluster의 감소, 양자점 밀도의 증가, 균일도의 향상, 종횡비(aspect ratio) 향상으로 설명된다. 온도에 따른 PL 세기와 PL 피크 에너지, PL 소멸 시간과 발광 파장에 따른 PL 소멸 시간을 측정하였다. As 공급과 차단을 2초로 하였을 때 cluster는 전혀 나타나지 않았고 양자점의 밀도는 증가하였으며 균일도와 종횡비도 향상되었다. 또한 S2는 가장 강한 PL 세기와 가장 긴 소멸 시간을 나타내었다. 이러한 결과는 AIG법을 이용하여 InAs 양자점의 크기, 조밀도, 균일도, 종횡비 등을 조절하여 원하는 파장대의 양자점을 성장할 수 있으며 발광 특성도 향상시킬 수 있음을 확인하였다. The optical properties of InAs quantum dots (QDs) grown on GaAs substrates grown by molecular beam epitaxy have been studied using photoluminescence (PL) and time-resolved PL measurements. InAs QDs were grown using an arsenic interruption growth (AIG) technique, in which the As flux was periodically interrupted by a closed As shutter during InAs QDs growth. In this study, the shutter of As source was periodically opened and closed for 1 (S1), 2 (S2), or 3 s (S3). For comparison, an InAs QD sample (S0) without As interruption was grown in a pure GaAs matrix for 20 s. The PL intensity of InAs QD samples grown by AIG technique is stronger than that of the reference sample (S0). While the PL peaks of S1 and S2 are redshifted compared to that of S0, the PL peak of S3 is blueshifted from that of S0. The increase of the PL intensity for the InAs QDs grown by AIG technique can be explained by the reduced InAs clusters, the increased QD density, the improved QD uniformity, and the improved aspect ratio (height/length). The redshift (blueshift) of the PL peak for S1 (S3) compared with that for S0 is attributed to the increase (decrease) in the QD average length compared to the average length of S0. The PL intensity, PL peak position, and PL decay time have been investigated as functions of temperature and emission wavelength. S2 shows no InAs clusters, the increased InAs QD density, the improved QD uniformity, and the improved QD aspect ratio. S2 also shows the strongest PL intensity and the longest PL decay time. These results indicate that the size (shape), density, and uniformity of InAs QDs can be controlled by using AIG technique. Therefore the emission wavelength and luminescence properties of InAs/GaAs QDs can also be controlled.

        • KCI등재

          Luminescence Properties of InAlAs/AlGaAs Quantum Dots Grown by Modified Molecular Beam Epitaxy

          권세라,류미이,송진동 한국진공학회 2014 Applied Science and Convergence Technology Vol.23 No.6

          Self-assembled InAlAs/AlGaAs quantum dots (QDs) on GaAs substrates were grown byusing modified molecular epitaxy beam in Stranski-Krastanov method. In order to study thestructural and optical properties of InAlAs/AlGaAs QDs, atomic force microscopy (AFM)and photoluminescence (PL) measurements are conducted. The size and uniformity of QDshave been observed from the AFM images. The average widths and heights of QDs areincreased as the deposition time increases. The PL spectra of QDs are composed of twopeaks. The PL spectra of QDs were analyzed by the excitation laser power- andtemperature-dependent PL, in which two PL peaks are attributed to two predominant sizesof QDs.

        • KCI등재

          Photoluminescence Studies of InP/InGaP Quantum Structures Grown by a Migration Enhanced Molecular Beam Epitaxy

          조일욱,류미이,송진동 한국진공학회 2016 Applied Science and Convergence Technology Vol.25 No.4

          InP/InGaP quantum structures (QSs) grown on GaAs substrates by a migration-enhanced molecular beam epitaxy method were studied as a function of growth temperature (T) using photoluminescence (PL) and emissionwavelength- dependent time-resolved PL (TRPL). The growth T were varied from 440℃ to 520℃ for the formation of InP/InGaP QSs. As growth T increases from 440℃ to 520℃, the PL peak position is blue-shifted, the PL intensity increases except for the sample grown at 520℃, and the PL decay becomes fast at 10 K. Emission-wavelengthdependent TRPL results of all QS samples show that the decay times at 10 K are slightly changed, exhibiting the longest time around at the PL peak, while at high T, the decay times increase rapidly with increasing wavelength, indicating carrier relaxation from smaller QSs to larger QSs via wetting layer/barrier. InP/InGaP QS sample grown at 460℃ shows the strongest PL intensity at 300 K and the longest decay time at 10 K, signifying the optimum growth T of 460℃.

        • KCI등재

          Effect of Growth Temperature on the Luminescence Properties of InP/GaP Short-Period Superlattice Structures

          변혜룡,류미이,송진동,이창렬 한국진공학회 2015 Applied Science and Convergence Technology Vol.24 No.1

          The optical properties of InP/GaP short-period superlattice (SPS) structures grown at varioustemperatures from 400oC to 490oC have been investigated by using temperature-dependentphotoluminescence (PL) and emission wavelength-dependent time-resolved PL measurements. The PL peak energy for SPS samples decreases as the growth temperature increases. Thedecreased PL energy of ∼10 meV for the sample grown at 425oC compared to that for400oC-grown sample is due to the CuPt-B type ordering, while the SPS samples grown at460oC and 490oC exhibit the significant reduction of the PL peak energies due to the combinedeffects of the formation of lateral composition modulation (LCM) and CuPt-B type ordering. The SPS samples with LCM structure show the enhanced carrier lifetime due to the spatialseparation of carriers. This study represents that the bandgap energy of InP/GaP SPS structurescan be controlled by varying growth temperature, leading to LCM formation and CuPt-Btype ordering.

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