Characterization and Control of GaN-based semiconductor interfaces for Fabrication of Field Effect Transistors

研究了金属/GaN、绝缘体/GaN和AlGaN/GaN异质结构在MESFET和HEMT器件中的界面特性。金属/GaN界面的表征(1)测量的各种金属/n， p-GaN肖特基二极管的I-V-T和C-V-T特性，包括理查德森图以及有效肖特基势垒高度（SBH）和理想因子的温度依赖性，可以用先前提出的“表面斑块”模型一致地解释。只有总斑块面积的10^<-5>的一小部分有效地降低了RT下的SBH，而它不影响从C-V曲线推断出的平波段SBH。(2) n- gan和p-GaN样品的高温I-V曲线对金属功函数的依赖较弱，s值较小，分别为0.28。(3)由于隧穿电流的存在，金属/n-AlGaN样品的有效SBH在室温下大大降低，但其真实SBH却比相应的金属/GaN样品大得多。金属/氮化镓界面的控制通过在氮气中退火，大大改善了I-V特性。氮化镓表面的热氧化导致SBH的增加，而二极管的特性没有明显的退化。氮化镓生长模拟；开发了包含层反位缺陷形成的MBE-GaN生长蒙特卡罗模拟程序，考察了生长条件对生长前表面平整度和缺陷密度的影响。深层特征；通过C-t测量，确定了SiO_2/GaN的体积阱和界面态的捕获截面和活化能。AlGaN/GaN异质结构的表征(1)通过I-V-T和C-V-T测量系统地揭示了AlGaN/GaN异质结构的电学性质。(2)提出了一种制备HEMT器件的新型阳极刻蚀工艺。

Interface properties of metal/GaN, insulator/GaN, and AlGaN/GaN heterostructure have been characterized for the fabrication of MESFET and HEMT devices.1. Characterization of metal/GaN interfaces ; (1) Measured I-V-T and C-V-T characteristics for various metal/n, p-GaN schottky diodes, which include the Richardson plots together with temperature dependences of the effective schottky barrier height (SBH) and the ideality factor, can be consistently explained by the previously proposed "surface patch" model. Only the fraction of the total patchy area of 10^<-5>effectively reduces the SBH at RT, while it does not affect the flat-band SBH deduced from the C-V curve. (2) The true SBHs determined from high-temperature I-V curve are weakly dependent on the metal work function with small S-values of 0.28 for n-and p-GaN samples, respectively. (3) Although the effective SBH for a metal/n-AlGaN sample is considerably lowered at RT, owing to a tunneling current, the true SBH is fairly larger as compared with that for corresponding metal/GaN sample.2. Control of Metal/GaN Interface ; I-V characteristics are greatly improved by an annealing in nitrogen. Thermal oxidation of GaN surface leads to increase of the SBH without noticeable degradation of the diode characteristics.3. Simulation of GaN growth ; A Monte Carlo simulation program for MBE-GaN growth, which incorporates formation of anti-site defect of layer, was developed, and the influence of growth conditions on the flatness of the growth front surface and on defect density was examined.4. Characterization of deep levels ; Capture cross-sections and activation energies for bulk traps and interface states at SiO_2/GaN were determined by C-t measurements.5. Characterization of AlGaN/GaN heterostructures ; (1) Electrical properties of AlGaN/GaN heterostructures were systematically revealed by I-V-T and C-V-T measurements. (2) A new anodic etching process has been developed for the fabrication of HEMT devices.