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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.
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.
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.
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.
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.
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.