半绝缘SiC单晶电阻率均匀性研究

采用非接触电阻率面分布(COREMA)方法对本实验室生长得到的2英寸(50 mm)4H和6H晶型半绝缘SiC单晶片进行电阻率测试,结果发现数据的离散性大,低者低于测试系统下限105Ω.cm,高者高于其上限1012Ω.cm,甚至在同一晶片内会出现小于105Ω.cm,105~1012Ω.cm和大于1012Ω.cm的不同区域,而有的晶片则电阻率的均匀性较好。将SiC电阻率测试结果与二次离子质谱(SIMS)对晶体内主要杂质V,B和N含量测试结果相结合,初步探讨得到引起掺钒SiC单晶电阻率的高低及均匀性的变化由补偿方式决定,在深受主补偿浅施主模式下,V的浓度控制在2×1016~3×1017cm-3,N的浓度控制在1×1016cm-3左右,深受主钒充分补偿浅施主氮,制备得到的SiC单晶具有半绝缘性,且电阻率均匀性好。     

MOCVD生长P型GaN的掺Mg量的研究

使用 MOCVD技术在 Al2 O3衬底上生长了 Ga N∶ Mg薄膜 .通过对退火后样品的光电性能综合分析 ,研究了掺 Mg量对生长 P型 Ga N的影响 .结果表明 :要获得高空穴载流子浓度的 P型 Ga N,Mg的掺杂量必须控制好 .掺 Mg量较小时 ,Ga N∶ Mg单晶膜呈现 N型导电 ,得不到 P型层 ;掺 Mg量过大时 ,会形成与 Mg有关的深施主 ,由于深施主的补偿作用 ,得不到高空穴浓度的 P型 Ga N.生长 P型 Ga N的最佳 Cp2 Mg/TMGa之比在 1 /660— 1 /330之间     

MOCVD生长P型GaN的掺Mg量的研究

使用MOCVD技术在Al2O3衬底上生长了GaN：Mg薄膜.通过对退火后样品的光电性能综合分析,研究了掺Mg量对生长P型GaN的影响.结果表明：要获得高空穴载流子浓度的P型GaN,Mg的掺杂量必须控制好.掺Mg量较小时,GaN：Mg单晶膜呈现N型导电,得不到P型层;掺Mg量过大时,会形成与Mg有关的深施主,由于深施主的补偿作用,得不到高空穴浓度的P型GaN.生长P型GaN的最佳Cp2Mg/TMGa之比在1/660-1/330之间     

PVT法掺钒SiC单晶生长电阻率变化规律研究

在采用COREMA方法测试SiC晶片电阻率时发现同一晶片电阻率相差较大,主要体现在高阻(>105Ω.cm量级)和低阻(<105量级)并存,有的甚至超高阻(>1012量级)和低阻并存,针对这一测试结果,开展了相关的实验研究,SiC单晶半绝缘性能的实现是通过在单晶生长过程中掺入深能级杂质V来补偿浅施主N和浅受主B,利用二次质谱(SIMS)对同一晶片不同区域的杂质元素V、N和B含量进行测试,结果发现晶片中V和N的含量都在1×1017量级时会出现同一晶片不同区域电阻率相差较大的情况,而当V含量在1×1017量级,N含量在5×1016量级以下时,可制备电阻率均匀性好的半绝缘SiC单晶。     

钒掺杂形成半绝缘6H-SiC的补偿机理

研究了钒掺杂生长半绝缘6H-SiC的补偿机理.二次离子质谱分析结果表明,非故意掺杂生长的6H-SiC中,氮是主要的剩余浅施主杂质.通过较深的钒受主能级对氮施主的补偿作用,得到了具有半绝缘特性的SiC材料.借助电子顺磁共振和吸收光谱分析,发现SiC中同时存在中性钒(V4 )和受主态钒(V3 )的电荷态,表明掺入的部分杂质钒通过补偿浅施主杂质氮,形成受主态钒,这与二次离子质谱分析结果相吻合.通过对样品进行吸收光谱和低温光致发光测量,发现钒受主能级在6H-SiC中位于导带下0.62eV处.     

钒掺杂形成半绝缘6H-SiC的补偿机理

研究了钒掺杂生长半绝缘6H-SiC的补偿机理.二次离子质谱分析结果表明,非故意掺杂生长的6H-SiC中,氮是主要的剩余浅施主杂质.通过较深的钒受主能级对氮施主的补偿作用,得到了具有半绝缘特性的SiC材料.借助电子顺磁共振和吸收光谱分析,发现SiC中同时存在中性钒(V4+)和受主态钒(V3+)的电荷态,表明掺入的部分杂质钒通过补偿浅施主杂质氮,形成受主态钒,这与二次离子质谱分析结果相吻合.通过对样品进行吸收光谱和低温光致发光测量,发现钒受主能级在6H-SiC中位于导带下0.62eV处.     

掺Sb的ZnO单晶的缺陷和性质研究

采用化学气相传输法生长了掺Sb的ZnO体单晶,生长温度为950℃. 与非掺ZnO单晶相比,掺Sb后ZnO单晶仍为n型,其自由电子浓度明显升高. X射线光电子能谱（XPS）测量结果表明,掺入的Sb在ZnO单晶中可能占据了Zn位,或处于间隙位置,形成了施主. 利用光致发光谱（PL）测量发现掺Sb后ZnO单晶发出蓝光,该蓝色荧光与浅施主有关. 这些结果表明在高温生长条件下,掺Sb后ZnO单晶中产生了高浓度的施主缺陷,因而难以获得p型材料.     

掺Sb的ZnO单晶的缺陷和性质研究

采用化学气相传输法生长了掺Sb的ZnO体单晶,生长温度为950℃.与非掺ZnO单品相比,掺Sb后ZnO单晶仍为n型,其自由电子浓度明显升高.x射线光电子能谱(XPS)测量结果表明.掺人的Sb在ZnO单晶中可能占据了Zn位,或处于间隙化置,形成了施主.利用光致发光谱(PL)测量发现掺Sb后ZnO单晶发出蓝光,该蓝色荧光与浅施主有关.这些结果表明在高温生长条件下,掺Sb后ZnO单晶中产生了高浓度的施主缺陷,因而难以获得P型材料.     

SI-GaAs材料的电学补偿

研究了ＨＰＬＥＣ工艺生长半绝缘砷化镓单晶过程中,熔体的化学剂量比对晶体深施主缺陷能级、浅受主碳的浓度以及晶体电学性能的影响．由Ｎ型半绝缘晶体的补偿机理对实验现象进行了解释,给出了既能保证晶体电学性能又可以使缺陷浓度较低的最佳熔体剂量比．并将近本征半导体的物理模型推广至半绝缘砷化镓单晶,得到了较理想的电阻率范围．     

掺氮6H-SiC单晶的电阻率、迁移率及自由载流子浓度

测试了国产和美国Cree公司生产的n型6H-SiC低温下的电学参数,包括电阻率、迁移率和自由载流子浓度,并用FCCS软件数据拟合分析得到两种SiC的杂质浓度和能级.实验结果表明:杂质浓度和补偿度对低温下SiC的电性能有很大影响,轻度补偿的掺氮6H-SiC是施主氮的两个能级共同起作用;而重度补偿的6H-SiC在低温时则是受主能级起作用,并且后者迁移率随温度变化曲线的峰值降低并右移.同时发现重度补偿的SiC在较低温度时由n型转变成了p型,并从理论上分析了产生这种现象的原因.     

迅速发展的SiC半导体技术

ＳｉＣ半导体技术在近几年得到了迅速发展。与其它半导体材料相比，ＳｉＣ独特的热特性和电特性，在功率和频率性能方面具有最高的品质因数。ＳｉＣ还适应于高温和辐射环境。从结构上看，ＳｉＣ具有多种同质异型体。本文概括介绍了ＳｉＣ材料特性、晶体生长和器件研制的进展情况，以及ＳｉＣ的应用前景。     

Optical and mechanical properties of C,Si, Ge,and 3C–SiC determined by first-principles theory using Heyd–Scuseria–Ernzerhof functional

Accurately calculating the band gap and electronic state density distribution of crystals is significant in determining optical properties. First-principles calculations were based on the projector-augmented-wave method with the Perdew–Burke–Ernzerhof generalized gradient approximation functional, pure density functional theory (DFT) and Heyd–Scuseria–Ernzerhof (HSE) hybrid functional. Such calculations account for the lattice parameters, electronic structure, optical properties, and mechanical properties of materials, which include the diamond-C and zinc blende structure of Si, Ge, and 3C–SiC in this study. The results obtained with HSE calculations is more accurate than that of the pure DFT calculations, and consistent with previous experimental values. The band structure and density of states of Si, Ge, and 3C–SiC indicate that these materials are indirect band gap materials. Based on HSE calculation, the band gap of Si and 3C–SiC is in accordance with previous experimental values. The imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient also matches previous experimental values. A corresponding relationship exists among the peak of the imaginary part of the analytical dielectric function, the refractive index, and the adsorption coefficient. The optical properties have a direct relationship with the distribution of the crystal band gap and electronic state density. The materials exhibit brittleness. Although 3C–SiC is not as hard and stiff as diamond, it is a better semiconductor than Si and Ge. The mechanical anisotropy of the four materials is inconspicuous. The anisotropy of diamond-C in terms of its Young's modulus is extremely inconspicuous.     

Bulk growth of single crystal silicon carbide

Silicon carbide (SiC) is a promising wide bandgap semiconductor material particularly suitable for future high power devices operable at high temperatures (>200 °C), at high frequencies, and in harsh environments (chemical and radiation) due to its unique physical and crystallographic properties. The absence of SiC liquid phase, under easily achievable growth conditions of pressure and temperature has created unique challenges for crystal growers.This paper reviews the basics of bulk growth processes, including source sublimation, mass transport of the Si and C species to the growing seed and crystallization. The growth process is shown to be a self-congruent phenomenon where the mass transport of the vapor species and the heat dissipation at the surface of phase transformation are interrelated. This process results in reduction of the growth velocity as a function of crystal thickness. Major mechanisms of defect generation in the grown crystal are discussed.     

Influence of 4H-SiC semi-insulating substrate purity on SiC metal-semiconductor field-effect transistor performance

The performances of silicon carbide (SiC) metal-semiconductor field-effect transistors (MESFETs) fabricated on conventional V-doped semi-insulating substrates and new V-free semi-insulating substrates have been compared. The V-free 4H-SiC substrates were confirmed by secondary ion mass spectrometry (SIMS). X-ray topography revealed significantly fewer micropipes and low-angle boundaries in V-free semi-insulating substrates than in conventional V-compensated substrates. Deep-level transient spectroscopy (DLTS) indicated that the spectra signals observed in conventional V-doped substrates were either reduced or disappeared in V-free substrates. The intrinsic deep levels in V-free substrates to make semi-insulating properties were also observed in DLTS spectra. Under various DC and RF stresses, SiC MESFETs fabricated on new V-free semi-insulating substrates showed superior device performance and stability.     

SiC晶体生长和应用

介绍了作为半导体材料应用的ＳｉＣ的主要性能，晶体生长研究进展及器件研制现状。     

Surface morphology of silicon carbide epitaxial films

Silicon carbide (SiC) semiconductor technology has been advancing rapidly, but there are numerous crystal growth problems that need to be solved before SiC can reach its full potential. Among these problems is a need for an improvement in the surface morphology of epitaxial films that are grown to produce device structures. Because of advantageous electrical properties, SiC development is shifting from the 6H to the 4H polytype. In this study of both 6H and 4H-SiC epilayers, atomic force microscopy and other techniques were used to characterize SiC epilayer surface morphology. Observed features included isolated growth pits a few micrometers in size in both polytypes and triangles (in 4H only) approximately 50 um in size for epilayers 3 um in thickness. Also observed in some epilayers were large steps with heights greater than 20 nm. We found that there are significant differences between the morphology of 6H and 4H epilayers grown under identical conditions. We were able to improve surface morphology by avoiding conditions that lead to excess silicon during the initial startup of the growth process. However, the observed morphological defect density in both 6H and 4H epilayers was still the order of 10⁴ cm^-2 and varied widely from run to run. As expected, we found that morphological defects in the SiC substrates play a role in the formation of some epilayer surface features.     

SiC单晶生长及其晶片加工技术的进展

回顾了SiC单晶的发展历史，总结了目前的发展状况，同时介绍了SiC单晶生长所需要的温场和生长工艺，最后介绍了SiC单晶的加工技术. 通过模拟计算与具体实验相结合的方法，调整坩埚在系统中的位置及优化坩埚设计可以得到理想温场. 近平微凸的温场有利于晶体小面的扩展，进而有利于减少缺陷提高晶体的质量. 由于SiC硬度非常高，对单晶后续的加工造成很多困难，包括切割和磨抛. 研究发现利用金刚石线锯切割大尺寸SiC晶体，可以得到低翘曲度、低表面粗糙度的晶片；采用化学机械抛光法，可以有效地去除SiC表面的划痕和研磨引入的加工变质层，加工后的SiC晶片粗糙度可小于1nm.     

掺V 6H-SiC单晶生长表面V析出相研究

采用扫描电镜(SEM)和光学显微镜(OM)观察物理气相传输(PVT)法生长掺V6H-SiC单晶新鲜表面时,发现具有特定形状的析出相,经SEM能谱(EDX)测试确定析出相的主要成分是V,推断其在单晶生长结束后的降温过程中产生。通过对V析出相的进一步研究发现其在数量、尺寸以及方向上都与单晶生长中心具有一定的关系,具有特定的分布规律,任何一个视场,析出相的取向只有两种,且数量相当,这一结果说明结晶动力学对V的掺入具有一定的影响;当结晶温度较高时,这种影响不明显,但随着结晶区温度的降低,影响加剧,从而出现析出相,且析出相的结晶行为完全受晶体表面形貌的制约。     

Time-Resolved Temperature Measurement of AlGaN/GaN Electronic Devices Using Micro-Raman Spectroscopy

We report on the development of time-resolved Raman thermography to measure transient temperatures in semiconductor devices with submicrometer spatial resolution. This new technique is illustrated for AlGaN/GaN HFETs and ungated devices grown on SiC and sapphire substrates. A temporal resolution of 200 ns is demonstrated. Temperature changes rapidly within sub-200 ns after switching the devices on or off, followed by a slower change in device temperature with a time constant of ~10 and ~140 mus for AlGaN/GaN devices grown on SiC and sapphire substrates, respectively. Heat diffusion into the device substrate is also demonstrated     

SiC/Si(111) film quality as a function of GeH4 flow in an MOCVD reactor

Due to large lattice and thermal expansion coefficient mismatches, SiC films grown on Si are usually low quality. To provide a more stable growth front we added Ge in the form of GeH₄ to the reactant gases in a MOCVD reactor. Several SiC films with Ge flow rates ranging from 0–50 sccm were grown on (111) Si substrates at 1000°C. TEM results show that the crystalline quality is amorphous or polycrystalline for Ge flow rates at or below 15 sccm. Samples grown at Ge flow rates at or exceeding 20 sccm have an initial layer of single crystalline 3C SiC followed by heavily twinned crystalline 3C SiC. In particular, the samples grown with 20–30 sccm Ge contain an 80 nm initial layer of reasonably high quality single crystal 3C SiC.