Atomic-Level Control of SiC and Device Applications

碳化硅是一种宽禁带的IV-IV化合物半导体材料。碳化硅的宽禁带使材料具有很高的击穿电场，约为硅或砷化镓击穿电场的十倍。碳化硅中的光学声子能量高达100-120 meV，这导致了高的饱和电子漂移速度(6H-碳化硅中的2×10~(-7)cm/S)和高的热导率(4.9W/Kcm)。这些优异的性能和晶体生长过程中可控的p型和n型掺杂使碳化硅成为一种非常有吸引力的半导体材料。研究了化学气相沉积(CVD)法在碳化硅(SiC0 0 0 1)衬底上的生长及其器件应用。提出了在无取向的碳化硅(0001)衬底上采用阶梯流生长(阶梯控制外延)的多晶型控制外延生长碳化硅的方法，并对其生长机理进行了讨论。在阶梯控制外延中，碳化硅的生长是由反应物在停滞层中的扩散控制的。利用描述在邻近的{0001}衬底上生长的模型，预测了生长模式由阶梯流动转变为二维成核的临界生长条件作为生长条件的函数。还研究了碳化硅外延层表面的阶跃聚束、成核和阶跃动力学。通过低温光致发光、霍尔效应和深能级测量，证实了高质量的碳化硅外延层。通过对氮施主和铝/硼受体的原位掺杂，获得了良好的宽范围掺杂可控性。研究了阶跃控制离轴层制备碳化硅器件的最新进展。高功率、高频、高温碳化硅器件的优异性能显示了碳化硅的内在潜力，为开发新型电子学奠定了基础。

Silicon carbide (SiC) is a IV-IV compound semiconductor material with a wide bandgap. The wide bandgaps of SiC give the material very high breakdown field, about ten times higher than that of Si or GaAs. The energies of optical phonons in SiC are as high as 100-120meV,which leads tohigh saturated electron drift velocity (2x10^7 cm/s in 6H-SiC) and high thermal conductivity (4.9W/Kcm). These outstanding properties and controllable p- and n-type doping during crystal growth make SiC a very attractive semiconductor material. Chemical vapor deposition (CVD) of silicon carbide (SiC) on SiC {0001} substrates and device applications have been investigated. Polytype-controlled epitaxial growth of SiC,which utilizes step-flow growth on off-oriented SiC {0001} substrates(step-controlled epitaxy), isproposed, and the detailedgrowth mechanism is discussed. In step-controlled epitaxy, SiC growth is controlled by the diffusion of reactants in a stagnant layr. Critical growth conditions where the growth mode changes from step-flow to two-dimensional nucleation are predicted as a function of growth conditions using a model describing SiC growth on vicinal {0001} substrates. Step bunching on the surfaces of SiC epilayrs, nucleation, and step-dynamics are also investigated. High quality of SiC epilayrs was elucidated through low-temperature photoluminescence, Hall effect, and deep level measurements. Excellent doping controllability in the wide range has been obtained by in-situ doping of a nitrogen donor and aluminum/boron acceptors. Recent progress in SiC device fabrication using step-controlledepitaxial layrs is studied. Intrinsic potential of SiC has been demonstrated in the excellent performance of high-power, high-frequency, and high-temperature SiC devices, which will exploit novel electronics.