• Journal of the Korean Vacuum Society
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• v.17 no.1
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• pp.34-39
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• 2008

We have investigated the characteristics of $Al_{0.55}Ga_{0.45}N$/GaN heterostructures with and without low-temperature (LT) AlN interlayer grown by metalorganic chemical vapor deposition. The structural and optical properties were systematically studied by Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), optical microscopy (OMS), scanning electron microscopy (SEM), and photoluminescence (PL). The Al content (x) of 55% and the structural properties of $Al_xGa_{1-x}N$/GaN heterostructures were investigated by using RBS and XRD, respectively. We carried out OMS and SEM experiments and obtained a decrease of the crack network in $Al_{0.55}Ga_{0.45}N$ layer with LT-AlN interlayer. A two-dimensional electron gas (2DEG)-related PL peak located at ${\sim}3.437eV$ was observed at 10 K for $Al_{0.55}Ga_{0.45}N$/GaN with LT-AlN interlayer. The 2DEG-related emission intensity gradually decreased with increasing temperature and disappeared at temperatures around 100 K. In addition, with increasing the excitation power above 3.0 mW, two 2DEG-related PL peaks were observed at ${\sim}3.411$ and ${\sim}3.437eV$. The observed lower-energy and higher-energy side 2DEG peaks were attributed to the transitions from the sub-band level and the Fermi energy level of 2DEG at the AlGaN/LT-AlN/GaN heterointerface, respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.375-375
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• 2010

CdTe as an absorber material is widely used in thin film solar cells with the heterostructure due to its almost ideal band gap energy of 1.45 eV, high photovoltaic conversion efficiency, low cost and stable performance. The deposition methods and preparation conditions for the fabrication of CdTe are very important for the achievement of high solar cell conversion efficiency. There are some rearranged reports about the deposition methods available for the preparation of CdTe thin films such as close spaced sublimation (CSS), physical vapor deposition (PVD), vacuum evaporation, vapor transport deposition (VTD), closed space vapor transport, electrodeposition, screen printing, spray pyrolysis, metalorganic chemical vapor deposition (MOCVD), and RF sputtering. The RF sputtering method for the preparation of CdTe thin films has important advantages in that the thin films can be prepared at low growth temperatures with large-area deposition suitable for mass-production. The authors reported that the optical and electrical properties of CdTe thin film were closely connected by the thickness-uniformity of the film in the previous study [1], which means that the better optical absorbance and the higher carrier concentration could be obtained in the better condition of thickness-uniformity for CdTe thin film. The thickness-uniformity could be controlled and improved by the some process parameters such as vacuum level and RF power in the sputtering process of CdTe thin films. However, there is a limitation to improve the thickness-uniformity only in the preparation process [1]. So it is necessary to introduce the external or additional method for improving the thickness-uniformity of CdTe thin film because the cell size of thin film solar cell will be enlarged. Therefore, the authors firstly applied the chemical mechanical polishing (CMP) process to improving the thickness-uniformity of CdTe thin films with a G&P POLI-450 CMP polisher [2]. CMP process is the most important process in semiconductor manufacturing processes in order to planarize the surface of the wafer even over 300 mm and to form the copper interconnects with damascene process. Some important CMP characteristics for CdTe were obtained including removal rate (RR), WIWNU%, RMS roughness, and peak-to-valley roughness [2]. With these important results, the CMP process for CdTe thin films was performed to improve the thickness-uniformity of the sputtering-deposited CdTe thin film which had the worst two thickness-uniformities of them. Some optical properties including optical transmittance and absorbance of the CdTe thin films were measured by using a UV-Visible spectrophotometer (Varian Techtron, Cary500scan) in the range of 400 - 800 nm. After CMP process, the thickness-uniformities became better than that of the best condition in the previous sputtering process of CdTe thin films. Consequently, the optical properties were directly affected by the thickness-uniformity of CdTe thin film. The absorbance of CdTe thin films was improved although the thickness of CdTe thin film was not changed.

• Journal of the Semiconductor & Display Technology
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• v.4 no.1 s.10
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• pp.43-48
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• 2005

Metaloganic chemical vapor deposition, also known as metalorganic vapor phase epitaxy has become one of the main techniques for growing thin, high purity films for compound semiconductors such as GaAs, InP, and InGaAsP. In this study, the distribution of growth rate and composition of InGaAsP, InGaP, and InGaAs films are studied using computational method. The influences of process parameters such as pressure, temperature and precursors' partial pressure on the growth rate and composition distributions are analyzed. The film growth rate is increased in the upstream part according to the increase of temperature but not in the downstream part. The Ga composition in InGaAsP film shows an asymptotic behavior for temperature variation but As composition varies significantly within the temperature range considered in the present study. The overall film growth rates of InGaP, InGaAs and InGaAsP are decreased with increasing the Ga/In ratios of the source gases. Pressure variation does not seem to be a significant parameter to the film growth. Film growth characteristics of tertiary films such as InGaP and InGaAs show similar trends to the quaternary film, InGaAsP.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.215-215
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• 2010

The feasibility of InSbTe (IST) chalcogenide materials prepared by metalorganic chemical vapor deposition (MOCVD) for phase-change memory (PRAM) applications was demonstrated. Films grown below $225^{\circ}C$ exhibited an amorphous structure, and the films grown at $300^{\circ}C$ Cincluded various crystalline phases such as In-Sb-Te, In-Sb, In-Te, and Sb-Te. The composition of the amorphous films grown at $225^{\circ}C$ was dependent on the working pressure. Films grown at $225^{\circ}C$ exhibited a smooth morphology with a root mean square(rms) roughness of less than 1nm, and the step-coverage of the films grown on a trench structure with an aspect ratio of 5:1 was greater than 90%. An increase in deposition time increased the filling rate, while retaining the conformal step-coverage. Films grown at $225^{\circ}C$ for 3h in a working pressure of $13{\times}10^2$ Pa exhibited a reproducible and complete filling in a trench structure.

• Journal of the Korean Vacuum Society
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• v.9 no.4
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• pp.373-378
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• 2000

There was a great difference in the formation kinetics of $TiO_2$ and $Bi_2O_3$ on silicon, but the growth of bismuth titanate (BIT) thin film was mainly limited by the formation of $TiO_2$. As a result, the BIT film was easy to be lack of bismuth. The pulse injection metalorganic chemical vapor deposition (MOCVD) process was introduced in order to overcome this problem by recovering the insufficient bismuth content in the film. By this pulse injection method, bismuth content was increased and also the uniform in-depth composition of the film was attained with a abrupt $Bi_4Ti_3O_{12}/Si$ interface. In addition, the crystallinity of $Bi_4Ti_3O_{12}$ thin film prepared by pulse injection process was greatly improved and the leakage current density was lowered by 1/2~1/3 of magnitude. Clockwise hysteresis of C-V was observed and the ferroelectric switching was confirmed for $Bi_4Ti_3O_{12}$ film deposited by pulse injection method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.21-21
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• 2006

21세기 정보통신 및 관련 소재의 연구방향은 새로운 기능성 확보, 극한적 제어성, 복합 및 융합이라는 경향으로 발전해 가고 있다. 반도체 기술 분야에서 현재의 공정적 한계를 극복하고 새로운 기능성을 부여하기 위해 나노 합성과 배열을 기본으로 하여 bottom-up 방식의 나노소자 구현이 큰 주목을 받고 있다. 나노선의 경우 나노 스케일의 dimension, 양자 제한 효과, 우수한 결정성, self-assembly, internal stress 등 기존 벌크형 소재에서 발견할 수 없는 새로운 기능성이 나타나고 있어 바이오, 에너지, 구조, 전자, 센서 등의 분야에서의 활용이 가능하다. 현재 국내외적으로 반도체 나노선으로 널리 연구되고 있는 재료는 ZnO, $SnO_2$, SiC 등이 중심이 되고 있다. 이중 ZnO 나 노선의 합성을 위해서는 thermal CVD, MOCVD, PLD, wet-chemical 등 다양한 방법이 사용되고 있다. 특히 MOCVD 방법에 의해 수직 정렬된 ZnO 나노막대를 성장할 수 있다. 이러한 나노막대는 MO 원료 및 산소 공급량을 적절히 제어함으로서 수직 배향 및 나노선의 구경 제어가 가능하며, 나노 막대의 크기 제어와 관련해서는 반응 관내의 DEZn 와 $O_2$의 양을 변화시켜 구조체의 크기를 수 십 ~ 수 백 나노미터의 크기로 제어할 수 있다. 본 연구는 이러한 ZnO 나노선의 성장과정에서 $210^{\circ}C$ 이하의 저온에서 성장한 ZnO 버퍼층을 이용해 나노구조의 형상을 제어하고자 하였다. 특히 ZnO 저온 버퍼층의 두께에 따라 나노막대의 직경변화, 수직배향성, 형상변화의 제어가 가능하였다. 나노막대의 특성 평가는 TEM, SEM, PL, XRD 등을 이용하여 구조적, 결정학적, 광학적 특성을 분석하였다.

• Korean Journal of Materials Research
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• v.10 no.4
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• pp.270-275
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• 2000

The Pt/YMnO$_3$/Y$_2$O$_3$/Si structure for metal/ferroelectric/insulator/semiconductor(MFIS)-FET was fabricated and effect of $Y_2$O$_3$layer on the properties of MFIS structure was investigated. The $Y_2$O$_3$ thin films on p-type Si(111) substrate deposited by Pulsed Laser Deposition were crystallized along (111) orientation irrespective of the deposition temperatures. Ferroelectric YMnO$_3$ thin films deposited directly on p-type Si (111) by MOCVD resulted in Mn deficient layer between Si and YMnO$_3$. However, YMnO$_3$ thin films having good quality and stoichiometric composition can be obtained by adopting $Y_2$O$_3$ buffer layer. The memory window of the $Y_2$O$_3$thin films with YMnO$_3$ film is greater than that of the YMnO$_3$ thin films without $Y_2$O$_3$ film after the annealing at 85$0^{\circ}C$ in vacuum ambient(100mtorr). The memory window is 1.3V at an applied voltage of 5V.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.63-63
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• 2012

편광분석법(ellipsometry)은 대상 물질의 유전율 함수의 실수부와 허수부를 Kramers-Kronig 관계식의 도움 없이 그 물질상수를 정확히 측정할 수 있는 매우 우수한 기술이다. 이 기술의 큰 장점 중 하나는 빛의 편광상태의 변화를 이용한 비파괴적인 방법으로써 실시간 측정이 가능하며, 박막의 두께측정의 오차범위는 0.1 nm 이하로써 매우 정확하다는 것이다. 본 연구자는 이러한 우수한 측정 기술인 편광분석법을 고진공의 분자살박막증착장치(MBE) 와 결합하여 AlSb, AlP의 유전율 함수를 측정하였다. Al 계열을 포함하는 반도체 화합물은 Al의 산소친화력이 강해 대기 중에서 순수한 유전율 함수를 얻기가 불가능하다. 하지만 본 연구실에서 초고진공 상태의 MBE 챔버에서 시료를 성장시키는 동시에 실시간으로 편광분석기를 이용하여 측정하였고, 지금까지 발표된 결과들 중 가장 순수한 상태의 AlSb 유전율 함수를 얻어낼 수 있었다. 또한 순수한 AlP의 유전함수를 측정할 수 있었고, 이는 편광분석기를 이용한 최초의 실험결과로써 이차미분을 이용한 전이점 분석결과 이론적인 전자밴드구조에서 E1, E1+${\Delta}1$, E2에 해당하는 밴드갭들을 확인할 수 있었다. 또한 표면의 원자배열 구조와 실시간으로 일어나는 그들의 역학적인 현상들에 관한 정보를 얻을 수 있는 surface photoabsorption (SPA)를 metalorganic chemical vapor deposition (MOCVD)에 장착하여 실시간 모니터링이 가능하도록 하였다. SPA를 이용하여 GaAs/AlGaAs 양자우물구조의 성장을 원자층 수준으로 실시간 모니터링을 할 수 있었다. 그리고 SPA를 이용하여 MOCVD 안에서 InP에 As가 흡착 및 탈착되는 현상을 분석하여, As의 흡착이 두 단계에 의해 이루어짐을 분석하였다. 그리고 편광분석법의 빠르고 정확한 측정 기술을 규칙적인 구조체에서 전자기파의 회절을 구할 수 있는 Rigorous Coupled-Wave Analysis (RCWA) 계산방법과 결합하여 나노구조의 기하학적인 모양을 정확하고 빠르게 구할 수 있었다. 본 연구를 위해 규칙적인 3차원 Si 구조체 제작하여 편광분석기로 측정하고 $SiO_2$와 표면 거칠기를 고려하여 RCWA로 분석한 결과, 규칙적인 Si 구조와 산화막 층까지 정확하게 분석할 수 있음을 확인하였다. 또한 규칙적인 나노구조분석 연구를 넘어 불규칙적인 나노구조에 대한 분석 가능성을 보이기 위해 InAs 양자점을 증착하여 분석하였고, 이를 통해 편광분석법과 RCWA를 이용하여 불규칙적인 나노구조의 모양과 크기, 분포의 분석이 가능함을 보였다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.9 no.6
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• pp.553-557
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• 1999

In order to investigate the optical properties of the $Al_XGa_{1-X}N/GaN$ thin film grown by metalorganic chemical vapor deposition (MOCVD) method, the photoluminescene (PL), photocurrent (PC) and persistent photoconductivity (PPC) measurements were carried out at room temperature. The band gap of the $A1_x$$Ga_{1-x}$N/GaN was determined to 3.70 eV by the PL and PC measurements. The PC measurement on the light illumination from the top of the $A1_x$$Ga_{1-x}$N/GaN thin film provides peaks at 3.70, 3.43, and around 2.2 eV. The PC spectrum by the illumination passing through from the substrate of the sample can be shown at 3.43 eV together with a broad tail band from the GaN band edge to around 2.23 eV. The photocurrent quenching and anomalous PPC decay observed in PPC measurements indicate that metastable electron states are fomed in the band gap of GaN layer to trap electrons which can be tunneled the potential barrier for long recovery time.

• Journal of the Korean Vacuum Society
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• v.15 no.2
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• pp.186-193
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• 2006

In this study, we analyzed the electrical and optical properties of metalorganic chemical vapor deposition grown InGaAs/InGaAsP/InP quantum dot(QD) molecules by using photoluminescence and deep-level transient spectroscopy. From these resulte, the energy levels of the large QDs are located at deeper region from the conduction band edge of the barrier than that of the small QDs, The large QDs seem to have the energy states more than two, and these energy levels of the QD molecules are located at 0.35, 0.42, and 0.45 eV from conduction band edge under -4 V reverse bias conditions. The energy levels are closely coupled under low reverse bias, and then decoupled as the bias voltage is increased.