플라즈마분자선에피탁시법을 이용한 사파이어 기판 위 질화알루미늄 박막의 에피탁시 성장

이효성,한석규,임동석,신은정,임세환,홍순구,정명호,이정용,Lee, Hyo-Sung,Han, Seok-Kyu,Lim, Dong-Seok,Shin, Eun-Jung,Lim, Se-Hwan,Hong, Soon-Ku,Jeong, Myoung-Ho,Lee, Jeong-Yong,Yao, Takafumi 한국재료학회 2011 한국재료학회지 Vol.21 No.11

We report growth of epitaxial AlN thin films on c-plane sapphire substrates by plasma-assisted molecular beam epitaxy. To achieve two-dimensional growth the substrates were nitrided by nitrogen plasma prior to the AlN growth, which resulted in the formation of a two-dimensional single crystalline AlN layer. The formation of the two-dimensional AlN layer by the nitridation process was confirmed by the observation of streaky reflection high energy electron diffraction (RHEED) patterns. The growth of AlN thin films was performed on the nitrided AlN layer by changing the Al beam flux with the fixed nitrogen flux at 860$^{\circ}C$. The growth mode of AlN films was also affected by the beam flux. By increasing the Al beam flux, two-dimensional growth of AlN films was favored, and a very flat surface with a root mean square roughness of 0.196 nm (for the 2 ${\mu}m$ ${\times}$ 2 ${\mu}m$ area) was obtained. Interestingly, additional diffraction lines were observed for the two-dimensionally grown AlN films, which were probably caused by the Al adlayer, which was similar to a report of Ga adlayer in the two-dimensional growth of GaN. Al droplets were observed in the sample grown with a higher Al beam flux after cooling to room temperature, which resulted from the excessive Al flux.

분자선 에피성장법으로 성장된 ZnSe/GaAs의 특성

김은도,손영호,조성진,황도원,Kim, Eun-Do,Son, Young-Ho,Cho, Seong-Jin,Hwang, Do-Weon 한국결정성장학회 2007 한국결정성장학회지 Vol.17 No.2

본 연구에서는 초고진공(UHV, ultra high vacuum) 분자선 에피성장(MBE, molecular beam epitaxy) 시스템을 제작하여, ZnSe/GaAs[001]을 증착하였고, 증착된 박막의 특성을 SEM(scanning electron microscopy), AFM(atomic force microscopy)으로 조사하여, 분자층 단위의 조밀하고 균일한 표면특성을 보이고 있음을 확인할 수 있었다 XRD(x-ray diffractometer)를 이용하여, GaAs[001]기판의 XRD peak 위치와 ZnSe 박막의 XRD peak 위치가 각자 일치함을 확인할 수 있었다. PL(photoluminescence)로는 대략 437nm에서 발광하는 것이 관측되었으며, 2인치 ZnSe 박막의 PL mapping을 측정하였다. We have installed an ultra high vacuum (UHV) molecular beam epitaxy (MBE) system and investigated into the characteristics of MBE-grown ZnSe/GaAs [001] using scanning electron microscopy (SEM), atomic force microscopy (AFM), we confirmed that layer's surface was dense and uniform of molecular layer. We used x-ray diffractometer (XRD) and confirmed two peaks correspond to GaAs [001] substrate and ZnSe epilayer, respectively. We observed photoluminescence (PL) peak approximately at 437 nm and measured PL mapping of 2 inch ZnSe epilayer.

Photoluminescence Studies of ZnO Films Fabricated by Using a Combination of a Hydrothermal Method and Plasma-assisted Molecular Beam Epitaxy Regrowth

박영빈,김병규,임재영,남기웅,김소아람,이상헌,정재학 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.3

ZnO films were deposited on Si (100) substrates by using a two-step growth process. In the firststep, ZnO nanorods were grown by using the hydrothermal method at 140 C for 5 min. In thesecond step, a ZnO amorphous layer was deposited on the ZnO nanorods by spin-coating. Aftercompletion of the growth process, the films were annealed at 800 C for 10 min, and a ZnO activelayer was deposited on top of the amorphous layer by using plasma-assisted molecular beam epitaxy. Further, temperature-dependent photoluminescence (PL) measurement were conducted to study theoptical properties of the prepared films. In the low-temperature PL spectra, emission peaks in thenear-band-edge region were observed at 3.370, 3.362, 3.347, 3.329, 3.317, 3.288, 3.263, 3.219, 3.191,and 3.116 eV; these peaks were attributed to free excitons, neutral donor bound excitons, neutralacceptor donor excitons, two electron satellites, and donor acceptor pairs, respectively. Thesepeaks were red-shifted, and their intensity decreased with increasing temperature. The bindingenergy of the donor was calculated as 43.1 meV by using the Haynes rule. Further, the valueand , factors in the equation for the energy of localized excitons of donors and acceptors wereobtained as 0.73 meV and 750 K, respectively, by fitting the free exciton (FX) peak according toVarshni’s equation. The full width at half-maximum of PL for the films was about 95.1 meV atroom temperature; moreover, the following values were obtained for the films by using theoreticalequations: the background impurity broadening, I0 = 62 meV, the parameter describing exciton-LO phonon interaction, ΙLO = 80 meV, LO phonon energy, ~!LO = 72 meV, and, the couplingstrength of an exciton-acoustic phonon interaction,ph = 0.087 meV/K Furthermore, the activationenergy was about 60.1 meV. ZnO films were deposited on Si (100) substrates by using a two-step growth process. In the firststep, ZnO nanorods were grown by using the hydrothermal method at 140 C for 5 min. In thesecond step, a ZnO amorphous layer was deposited on the ZnO nanorods by spin-coating. Aftercompletion of the growth process, the films were annealed at 800 C for 10 min, and a ZnO activelayer was deposited on top of the amorphous layer by using plasma-assisted molecular beam epitaxy. Further, temperature-dependent photoluminescence (PL) measurement were conducted to study theoptical properties of the prepared films. In the low-temperature PL spectra, emission peaks in thenear-band-edge region were observed at 3.370, 3.362, 3.347, 3.329, 3.317, 3.288, 3.263, 3.219, 3.191,and 3.116 eV; these peaks were attributed to free excitons, neutral donor bound excitons, neutralacceptor donor excitons, two electron satellites, and donor acceptor pairs, respectively. Thesepeaks were red-shifted, and their intensity decreased with increasing temperature. The bindingenergy of the donor was calculated as 43.1 meV by using the Haynes rule. Further, the valueand , factors in the equation for the energy of localized excitons of donors and acceptors wereobtained as 0.73 meV and 750 K, respectively, by fitting the free exciton (FX) peak according toVarshni’s equation. The full width at half-maximum of PL for the films was about 95.1 meV atroom temperature; moreover, the following values were obtained for the films by using theoreticalequations: the background impurity broadening, I0 = 62 meV, the parameter describing exciton-LO phonon interaction, ILO = 80 meV, LO phonon energy, ~!LO = 72 meV, and, the couplingstrength of an exciton-acoustic phonon interaction,ph = 0.087 meV/K Furthermore, the activationenergy was about 60.1 meV.

Deposition of ZnO thin films on GaN substrates

T. Peng,Q. M. Fu,C. Liu 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.-

ZnO thin films were deposited by electron-beam evaporation on undoped GaN and p-GaN substrates, which were grown by radio-frequency assisted molecular-beam epitaxy. It has been found that rotation of the substrate during deposition has a crucial effect on the morphology and microstructure that can be varied from nanorod growth to two-dimensional ZnO thin film growth when the substrate is changed from stationary to rotatory. Under optimized growth conditions, the morphologies of ZnO thin films are similar to those of GaN substrates. ZnO thin films were deposited by electron-beam evaporation on undoped GaN and p-GaN substrates, which were grown by radio-frequency assisted molecular-beam epitaxy. It has been found that rotation of the substrate during deposition has a crucial effect on the morphology and microstructure that can be varied from nanorod growth to two-dimensional ZnO thin film growth when the substrate is changed from stationary to rotatory. Under optimized growth conditions, the morphologies of ZnO thin films are similar to those of GaN substrates.

Trap-assisted high responsivity of a phototransistor using bi-layer MoSe₂ grown by molecular beam epitaxy

Choi, Yoon-Ho,Kwon, Gi-Hyeon,Jeong, Jae-Hun,Jeong, Kwang-Sik,Kwon, Hyeokjae,An, Youngseo,Kim, Minju,Kim, Hyoungsub,Yi, Yeonjin,Im, Seongil,Cho, Mann-Ho Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.494 No.-

<P><B>Abstract</B></P> <P>The transition metal dichalcogenides (TMDs) have great optical absorption and mobility in a subnanometer thickness. The MoSe<SUB>2</SUB> among TMDs is significantly interested as an active layer in optical devices because it is superior to other TMDs in light absorption. Herein, we investigated the mechanism and characteristics of phototransistors using bi-layer MoSe<SUB>2</SUB> film grown by molecular beam epitaxy. The interaction between the Al<SUB>2</SUB>O<SUB>3</SUB> and MoSe<SUB>2</SUB> was explored by X-ray and ultraviolet photoelectron spectroscopy, which showed that the chemical bonding and energy-band bending in the MoSe<SUB>2</SUB> due to the electron doping. The optical devices exhibited well-controlled performance of the phototransistors with gate bias and illumination power-density, resulting in superior photoresponsivity (<I>R</I>) of 242 A/W. The mechanism of the <I>R</I> was fully interpreted by the change in quasi Fermi levels, defect states, mobility, and metal contact. Especially, capturing the electrons (holes) generated in the defect states increases the probability that the untrapped holes (electrons) reach the source and drain electrode, resulting in the high <I>R</I>. In addition, the decay mechanism was described by lowering the temperature, which persistent photocurrent was not observed at the low temperature. Finally, the performance of logic gates composed of the MoSe<SUB>2</SUB> demonstrates its applicability to future photo-sensing systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The phototransistor was fabricated with the bilayer-MoSe<SUB>2</SUB> grown by molecular beam epitaxy. </LI> <LI> The phototransistor exhibited high photoresponsivity(<I>R</I>) and external quantum efficiency(<I>EQE</I>). </LI> <LI> The mechanism of the high <I>R</I> and <I>EQE</I> was interpreted by the defects, mobility, and interfaces. </LI> </UL> </P>

Molecular Beam Epitaxy of InAs/AlSb HFET's on Si and GaAs Substrates

Oh, Jae-Eung,Kim, Mun-Deok The Institute of Electronics and Information Engin 2006 Journal of semiconductor technology and science Vol.6 No.3

High electron mobility transistors with InAs channels and antimonide barriers were grown on Si and GaAs substrates by means of molecular beam epitaxy. While direct growth of Sb materials on Si substrate generates disordered and coalescences 3-D growth, smooth and mirror-like 2D growth can be repeatedly obtained by inserting AlSb QD layers between them. Room-temperature electron mobilities of over 10,000 $cm^2/V-s$ and 20,000 $cm^2/v-s$ can be routinely obtained on Si and GaAs substrates, respectively, after optimizing the buffer structure as well as maintaining InSb-like interface.

Epitaxial growth of low temperature GaN using metal migration enhanced epitaxy for high-quality InGaN/GaN heterojunctions

Woo, Hyeonseok,Kim, Jongmin,Cho, Sangeun,Jo, Yongcheol,Roh, Cheong Hyun,Lee, Jun Ho,Seo, Yong Gon,Kim, Hyungsang,Im, Hyunsik,Hahn, Cheol-Koo Elsevier 2018 Superlattices and microstructures Vol.120 No.-

<P><B>Abstract</B></P> <P>An effective method for high-quality molecular beam epitaxy growth of InGaN/GaN multiple quantum wells is demonstrated by inserting an ultrathin low temperature GaN (LT-GaN) interlayer between InGaN well and conventional high temperature GaN (HT-GaN) barrier layers. The LT-GaN interlayer is fabricated using metal migration enhanced epitaxy at the same growth temperature for InGaN. A smooth LT-GaN surface with a low defect density is obtained and indium decomposition is not observed. Large emission blueshift is significantly suppressed and narrow linewidth photoluminescence emission is achieved. The improved optical properties of the InGaN/GaN MQWs with LT-GaN interlayers are due to reduced compositional fluctuation and improved interface roughness.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High quality epi-GaN is grown at a low temperature (590 °C) using metal migration enhanced MBE epitaxy. </LI> <LI> Surface roughness and defect density of low-temperature GaN are considerably improved. </LI> <LI> InGaN/GaN QWs with low-temperature epi-GaN insertion show significantly suppressed indium decomposition and single PL peak. </LI> </UL> </P>

Epitaxial Growth of GaN Films on Atomically Stepped (0001) Lithium-niobate (LiNbO_3) Substrates

Man Hoai Nam,양우철,김문덕,박인성 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.51

The structural properties of GaN films grown epitaxially on atomically-flat lithium niobate (LiNbO_3) substrates were investigated. Prior to GaN film growth, high-temperature treatment of the as-received LiNbO_3 removed surface damage and produced atomically stepped surfaces with an average roughness of ∼0.11 nm. The micro-steps were nearly parallel and periodic over the entire substrate surface. The step terrace width was ∼212 nm, and the average step height was ∼0.25 nm. GaN thin films were grown on flat surfaces with AlN buffer layers and GaN buffer layers grown at low temperature by using molecular beam epitaxy. Atomic force microscopy measurements showed a typical Ga-face GaN surface with spiral hillocks. The average roughness of the GaN film was ∼0.56 nm. X-ray diffraction (XRD) measurements indicated that the GaN (0001) plane was parallel to the (0001) plane of the LiNbO_3 substrate. The full width at half-maximum of the XRD rocking curve for GaN (0002) was ∼122.14 arcsec, which is comparable to that of highquality GaN films grown on other common substrates. Using transmission electron microscopy, we observed that the GaN epitaxial layers grown on LiNbO<SUB>3</SUB> had a crystalline relationship of (0001) GaN//(0001) LiNbO_3 with [10-10] GaN//[11-20] LiNbO_3. The successful growth of an epitaxial wide-band-gap GaN film on nonlinear optical LiNbO_3 is promising for the development of integrated multi-functional optoelectric devices on ferroelectrics.

Molecular Beam Epitaxy of InAs/AlSb HFET’s on Si and GaAs Substrates

Jae-Eung Oh,Mun Deok Kim 대한전자공학회 2006 Journal of semiconductor technology and science Vol.6 No.3

High electron mobility transistors with InAs channels and antimonide barriers were grown on Si and GaAs substrates by means of molecular beam epitaxy. While direct growth of Sb materials on Si substrate generates disordered and coalescences 3-D growth, smooth and mirror-like 2D growth can be repeatedly obtained by inserting AlSb QD layers between them. Room-temperature electron mobilities of over 10,000 ㎠/V-s and 20,000 ㎠/v-s can be routinely obtained on Si and GaAs substrates, respectively, after optimizing the buffer structure as well as maintaining InSb-like interface.

Optical properties and carrier dynamics of GaAs/GaInAs multiplequantum- well shell grown on GaAs nanowire by molecular beam epitaxy

Kwangwook Park,Sooraj Ravindran,주건우,Jung-Wook Min,Seokjin Kang,명노성,Sang-Youp Yim,조용륜,김봉중,Yong-Tak Lee 한국물리학회 2016 Current Applied Physics Vol.16 No.12

GaAs/GaInAs multiple-quantum-well (MQW) shells having different GaInAs shell width formed on the surface of self-catalyzed GaAs core nanowires (NWs) are grown on (100) Si substrate using molecular beam epitaxy. The photoluminescence emission from GaAs/GaInAs MQW shells and the carrier lifetime could be varied by changing the width of GaInAs shell. Time-resolved photoluminescence measurements showed that the carrier lifetime had a fast and slow decay owing to the mixing of wurtzite and zincblende structures of the NWs. Furthermore, strain relaxation caused the carrier lifetime to decrease beyond a certain thickness of GaInAs quantum well shells.