Thermal degradation of Ohmic contacts on semipolar (11–22) GaN films grown on m-plane (1–100) sapphire substrates
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Ohmic contact
Contact resistance
A status report is given on the metalorganic chemical vapor deposition (MOCVD) of high-temperature superconducting thin films. The advantages of MOCVD processing manifest themselves in the quality of the films produced, and in the economy of the process. Metalorganic precursor requirements, deposition parameters and film properties are discussed. Also difficulties have been identified in making MOCVD a manufacturing technology. To solve these problems, future research directions are proposed.
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The conditions for obtaining epitaxial InN layers on a ‐plane (11–20) sapphire with a GaN buffer layer by MOCVD method are determined for the first time. Comparative studies show that InN layers on a ‐plane sapphire have higher structural perfection and improved photoluminescence properties compared to those grown on c ‐plane sapphire. Formation of indium clusters in the InN layers along with the conditions impeding their appearance is considered.
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The main goal of this work is to minimize stress fields due to the mismatch in lattice constants and thermal expansion coefficients between GaN and sapphire by using the chemical and physical changes of the sapphire (0001) substrate. Effects of N/sup +/-implanted sapphire (0001) substrate on GaN epilayer by metal organic chemical vapor deposition (MOCVD) were investigated. It is our intention to examine the possibility of employing the N/sup +/-implantation treatment of the sapphire (0001) substrate to improve the properties of GaN epilayer grown by MOCVD.
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A technique is described to estimate the contact resistance of an ohmic contact, under dynamic conditions, applied to a high resistivity photoconductor. It has been used to estimate the contact resistance of an ohmic contact (Au–Ge) applied to a semiinsulating Cr-doped GaAs (p≊108 W cm).
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Electrical contacts
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상온 혹은 고온 스퍼터링, CVD, MOCVD(metal-organic chemical vapor deposition)등 ZrO2 박막을 제조하는 여러 증착 방법들이 존재하나 특히 CVD법은 폭 넓고 다양한 공정 가능성과 조건 그리고 정밀한 공정 제어로 인해 각광 받아 왔다. 더욱이 MOCVD법은 낮은 온도에서도 양질의 박막을 증착 가능하게 해준다. 그리하여 MOCVD법은 박막 증착에 있어 가장 최적화된 방법으로 인정받고 있다. 본 연구에서는 이보다 한단계 더나가 ZTB 전구체를 이용하여 Si substrate에 ZrO2 단성분계 산화재료를 RTMOCVD (rapid thermal metalorganic chemical vapor deposition) 방법으로 구성하고, 후속 열처리를 통해서 제조된 물질의 결정화로 단일상 물질을 형성하여 다양한 두께의 박막형성을 유도하고 각두께에 따른 열처리 후의 단일상 박막의 결정성, 물성 변화 및 표면 roughness 등에 미치는 영향 SEM, TEM, XRD등의 분석기기들을 이용하여 분석 연구하였다.
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In this article, a scheme for fabricating low resistance Ohmic contacts to n-GaN was developed. This approach takes advantage of Ar plasma treatment and thermal annealing in forming gas ambient. As a result, the adjustment of Ar flow rate was very effective in improving the contact resistance. After proper Ar plasma treatment, the contact resistance and specific contact resistance of as-deposited Ohmic contacts were reduced to 0.362 Ω mm and 3.9×10−5 Ω cm2, respectively. Low contact resistance (0.103 Ω mm) and specific contact resistance (3.2×10−6 Ω cm2) were obtained after annealing in N2 gas ambient. By performing thermal annealing in forming gas ambient, even lower contact resistance (0.093 Ω mm) and specific contact resistance (2.6×10−6 Ω cm2) were successfully achieved, indicating that the electrical characteristics of Ohmic contacts would not be affected by the effect of hydrogen passivation of dopants in n-GaN.
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We show that ε1-Cu3Ge forms a low-resistance ohmic contact to n-type GaAs. The ε1-Cu3Ge contact exhibits a planar and abrupt interface and contact resistivity of 6.5×10−7 Ω cm2 which is considerably lower than that reported for Ge/Pd and AuGeNi contacts on n-type GaAs with similar doping concentrations (∼1×1017 cm−3). The contact is electrically stable during annealing at temperatures up to 450 °C. We also show that in the Ge/Cu/n-type GaAs system, the contact remains ohmic over a wide range of Ge concentration that extends from 15 to 40 at. %. n-channel GaAs metal–semiconductor field-effect transistors using the ε1-Cu3Ge ohmic contacts demonstrate a higher transconductance compared to devices with Ge/Pd and AuGeNi contacts.
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Contact resistance
Transconductance
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Optical and structural properties of light emitting diode (LED) structures grown by MOCVD on both GaN/sapphire templates and sapphire substrates are presented. The GaN/sapphire 3–5 μm thick templates were grown by HVPE on c-plane sapphire. Si-doping can alter defect formation in the templates. Depending on the LED structure design and growth conditions, the EL peak position varied in the range of 380 to 430 nm. MOCVD deposition improved the morphology of the HVPE-grown surface. The LED structures grown on GaN/sapphire templates had similar or superior EL intensity compared to samples grown on sapphire substrates.
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A status report is given on the metalorganic chemical vapor deposition (MOCVD) of high-temperature superconducting thin films. The advantages of MOCVD processing manifest themselves in the quality of the films produced, and in the economy of the process. Metalorganic precursor requirements, deposition parameters and film properties are discussed. Also difficulties have been identified in making MOCVD a manufacturing technology. To solve these problems, future research directions are proposed.
Deposition
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