N极性GaN/AlGaN异质结二维电子气模拟

通过自洽求解薛定谔方程和泊松方程,较系统地研究了GaN沟道层、AlGaN背势垒层、Si掺杂和AlN插入层对N极性GaN/AlGaN异质结中二维电子气(2DEG)的影响,分析表明,GaN沟道层厚度、AlGaN背势垒层厚度及Al组分变大都能一定程度上提高二维电子气面密度,AlGaN背势垒层的厚度和Al组分变大也可提高二维电子气限阈性,且不同的Si掺杂形式对二维电子气的影响也有差异,而AlN插入层在提高器件二维电子气面密度、限阈性等方面表现都较为突出,在模拟中GaN沟道层厚度小于5nm时无法形成二维电子气,超过20nm后二维电子气面密度趋于饱和,而AlGaN背势垒厚度超过40nm后二维电子气也有饱和趋势,对均匀掺杂和delta掺杂而言AlGaN背势垒层Si掺杂浓度超过5×10~(19)cm~(-3)后2DEG面密度开始饱和,而厚度为2nmAlN插入层的引入会使2DEG面密度从无AlN插入层时的0.93×10~(13)cm~(-2)提高到1.17×10~(13)cm~(-2)。     

Ⅲ族氮化物异质结构二维电子气研究进展

本文总结了近年来Ⅲ族氮化物半导体异质结构二维电子气的研究进展。从Ⅲ族氮化物材料晶格结构和特有的极化性质出发,重点讨论了AlGaN/GaN异质结构中二维电子气的性质,总结分析了异质结构中Al组分、势垒层厚度、应变弛豫度、掺杂等对二维电子气浓度和迁移率的影响,同时还涉及AlGaN/GaN/AlGaN,AlGaN/AlN/GaN和AlGaN/InGaN/GaN等异质结构二维电子气性质。     

Ⅲ族氮化物异质结构二维电子气研究进展

本文总结了近年来Ⅲ族氮化物半导体异质结构二维电子气的研究进展。从Ⅲ族氮化物材料晶格结构和特有的极化性质出发,重点讨论了AlGaN/GaN异质结构中二维电子气的性质,总结分析了异质结构中Al组分、势垒层厚度、应变弛豫度、掺杂等对二维电子气浓度和迁移率的影响,同时还涉及AlGaN/GaN/AlGaN,AlGaN/AlN/GaN和AlGaN/InGaN/GaN等异质结构二维电子气性质。     

高温AlN插入层对AlGaN/GaN异质结材料和HEMTs器件电学特性的影响

研究了在GaN缓冲层中插入40 nm厚高温AlN层的GaN外延层和AlGaN/GaN异质结材料, AlN插入层可以增加GaN层的面内压应力并提高AlGaN/GaN高电子迁移率晶体管（HEMTs）的电学特性. 在精确测量布拉格衍射角的基础上定量计算了压应力的大小. 增加的压应力一方面通过增强GaN层的压电极化电场, 提高了AlGaN/GaN异质结二维电子气（2DEG）面密度, 另一方面使AlGaN势垒层对2DEG面密度产生的两方面影响相互抵消. 同时, 这种AlN插入层的采用降低了GaN与AlGaN层之间的 关键词： 高温AlN插入层 AlGaN/GaN异质结 二维电子气 应力     

AlxGa1-xN/GaN异质结构中Al组分对二维电子气性质的影响

通过用数值计算方法自洽求解薛定谔方程和泊松方程,研究了Al组分对AlxGa1-xN/GaN异质结构二维电子气性质的影响,给出了AlxGa1-xN/GaN异质结构二维电子气分布和面密度,导带能带偏移以及子带中电子分布随AlxGa1-xN势垒层中Al组分的变化关系,并用AlxGa1-xN/GaN异质结构自发极化与压电极化机理和能带偏移对结果进行讨论分析.     

AlGaN/GaN异质结构中极化与势垒层掺杂对二维电子气的影响

从Ⅲ族氮化物中压电极化对应变弛豫度的依赖关系出发，通过自洽求解薛定谔方程和泊松方程,分别研究了自发极化、压电极化和AlGaN势垒层掺杂对AlxGa1-xN/GaN异质结构二维电子气的浓度、分布、面密度以及子带分布等性质的影响.结果表明：二维电子气性质强烈依赖于极化效应,不考虑AlGaN势垒层掺杂，当Al组分为0.3时，由极化导致的二维电子气浓度达1.6×10--13cm-2,其中压电极化对二维电子气贡献为0.7×10-13cm-2，略小于自发极化的贡献(0.9×10-13cm-2)，但为同一数量级，因而通过控制AlGaN层应变而改变极化对于提高二维电子气浓度至关重要. AlGaN势垒层掺杂对二维电子气的影响较弱, 当掺杂浓度从1×10-17增加到1×10-18cm-3时，二维电子气面密度增加0.2×10-13cm-2. 关键词： AlxGa1-xN/GaN 异质结构 二维电子气 自发极化 压电极化     

AlxGa1-xN/GaN异质结构中Al组分对二维电子气性质的影响

通过用数值计算方法自洽求解薛定谔方程和泊松方程，研究了Al组分对Al_xGa1-xN/GaN异质结构二维电子气性质的影响，给出了Al_xGa_{1-x< /sub>N/GaN异质结构二维电子气分布和面密度，导带能带偏移以及子带中电子分布随AlxGa 1-xN势垒层中Al组分的变化关系，并用AlxGa1-xN/GaN 异质结构自发极化与压电极化机理和能 关键词： x}Ga_1-xN/GaN异质结构')" href="#">Al_xGa_1-xN/GaN异质结构 二维电子气 自发极化 压电极化     

结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响

基于漂移-扩散传输模型、费米狄拉克统计模型以及Shockley-Read-Hall复合模型等,通过自洽求解薛定谔方程、泊松方程以及载流子连续性方程,模拟研究了材料结构参数对N极性面GaN/InAlN高电子迁移率晶体管性能的影响及其物理机制.结果表明,增加GaN沟道层的厚度(5—15 nm)与InAlN背势垒层的厚度(10—40 nm),均使得器件的饱和输出电流增大,阈值电压发生负向漂移.器件的跨导峰值随Ga N沟道层厚度的增加与InAlN背势垒层厚度的减小而减小.模拟中,各种性能参数的变化趋势均随GaN沟道层与InAlN背势垒层厚度的增加而逐渐变缓,当GaN沟道层厚度超过15 nm、InAlN背势垒层厚度超过40 nm后,器件的饱和输出电流、阈值电压等参数基本趋于稳定.材料结构参数对器件性能影响的主要原因可归于器件内部极化效应、能带结构以及沟道中二维电子气的变化.     

ZnMgO/ZnO异质结构中二维电子气的研究

论文根据ZnMgO/ZnO异质结构二维电子气的能带结构及相关理论模型, 采用一维Poisson-Schrodinger方程的自洽求解, 模拟计算了ZnMgO/ZnO异质结构中二维电子气的分布及其对ZnMgO势垒层厚度及Mg组分的依赖关系. 研究发现该异质结构中ZnMgO势垒层厚度存在一最小临界值: 当垒层厚度小于该临界值时, 二维电子气消失, 当垒层厚度大于该临界值时, 其二维电子气密度随着该垒层厚度的增加而增大; 同时研究发现ZnMgO势垒层中Mg组分的增加将显著增强其二维电子气的行为, 导致二维电子气密度的明显增大; 论文对模拟计算获得的结果与相关文献报道的实验结果进行了比较, 并从极化效应和能带结构的角度进行了分析和讨论, 给出了合理的解释. 关键词： 氧化锌 二维电子气 异质结构 理论计算     

AlGaN/GaN异质结载流子面密度测量的比较与分析

对MOCVD技术在蓝宝石衬底上生长的不同Al组分AlGaN/GaN异质结进行了范德堡法Hall测量和电容-电压(C-V)测量，发现Hall测量载流子面密度值大于C-V测量值，并且随着AlGaN层Al组分的增加，两种测量值都在增加，同时它们的差值也在增加.认为产生这一结果的原因有两方面.一方面，Ni/Au肖特基金属淀积在AlGaN/GaN异质结上，改变了AlGaN势垒层的表面状态，使得一部分二维电子气(2DEG)电子被抽取到空的施主表面态中，从而减小了AlGaN/GaN异质结界面势阱中的2DEG浓度.随着势垒层Al组分的增加，AlGaN层产生了更多的表面态，从而使得更多的电子被抽取到了空的表面态中.另一方面，由于C-V测量本身精确度受到串联电阻的影响，使得测量电容小于实际电容，从而低估了载流子浓度.     

Polarization effects simulation of AlGaN/GaN heterojunction by using a symbolistic δ-doping layer

Polarization effects in AlGaN/GaN heterojunction are simulated based on a traditional semiconductor device simulator. A δ doping layer is purposely inserted at the interface of the heterojunction in the simulation, so the ionized donors or acceptors can represent polarization-induced positive or negative fixed charges. The free electron distribution of single AlGaN/GaN heterostructures with Ga-face and N-face growth is compared, and the results of the simulation show that carrier confinement takes place only in the former structure. The dependence of sheet density of free electrons at the interface of Ga-face growth AlGaN/GaN on Al composition and the thickness of AlGaN is also investigated. The consistency of simulation results with the experiments and calculations reported by other researchers shows that this method can be effectively used to deal with the polarization effects in the simulation of GaN-based heterojunction devices.     

The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.     

Theoretical analytic model for RESURF AlGaN/GaN HEMTs

In this paper, we propose a two-dimensional(2D) analytic model for the channel potential and electric field distribution of the RESURF AlGaN/GaN high electron mobility transistors(HEMTs). The model is constructed by two-dimensional Poisson's equation with appropriate boundary conditions. In the RESURF AlGaN/GaN HEMTs, we utilize the RESURF effect generated by doped negative charge in the AlGaN layer and introduce new electric field peaks in the device channels,thus, homogenizing the distribution of electric field in channel and improving the breakdown voltage of the device. In order to reveal the influence of doped negative charge on the electric field distribution, we demonstrate in detail the influences of the charge doping density and doping position on the potential and electric field distribution of the RESURF AlGaN/GaN HEMTs with double low density drain(LDD). The validity of the model is verified by comparing the results obtained from the analytical model with the simulation results from the ISE software. This analysis method gives a physical insight into the mechanism of the AlGaN/GaN HEMTs and provides reference to modeling other AlGaN/GaN HEMTs device.     

Two-dimensional electron gas densities in AlGaN/AlN/GaN heterostructures

The dependence of two-dimensional electron gas (2DEG) density and distribution in an Al_xGa_1-xN/AlN/GaN heterostructure on the thicknesses of the Al_xGa_1-xN barrier layer and the AlN interfacial layer are investigated theoretically. A competitive contribution of the AlGaN and AlN layers to the 2DEG density is revealed. For an AlN interfacial layer thinner than a critical value d_cAlN, the 2DEG density is dominated by the AlGaN barrier and the 2DEG density increases with the increase of the AlGaN barrier thickness, as in the case of a simple AlGaN/GaN heterostructure. While the AlN interfacial layer will take the dominant contribution to the 2DEG density as its thickness exceeds d_cAlN. In this case, the increase of AlGaN barrier layer thickness leads to the decrease of the 2DEG density. Detailed calculations show that the critical AlN thickness increases with the increase of Al content in the AlGaN barrier. PACS 85.30.De; 73.40.Kp; 02.60.Cb     

Strong quantum confinement and high carrier concentration in AlGaN/InGaN/GaN heterostructure field-effect transistors

In this letter, we investigate the carrier features in AlGaN/InGaN/GaN heterostructure field-effect transistors. A study of charge control in the AlGaN/InGaN/GaN structure is performed by self-consistently solving Schrödingers equation in conjunction with Poissons equation. The results indicate that the concentration of two-dimensional electron gas can be largely increased with the incorporation of an InGaN layer. Both carrier density and quantum confinement are very sensitive to the strain in the InGaN channel layer. These novel features are attributed to the strong polarization effect in the AlGaN/InGaN and InGaN/GaN interfaces. PACS 85.30.De; 85.30.Tv; 77.65.Ly; 85.35.Be; 02.60.Cb     

Simulation of polarization effects in AlGaN/GaN heterojunction

Because of their large band-gap, large high-field electron velocity, large breakdownfield, and large thermal conductivity, GaN and its heterojunction with AlGaN and InGaNhave foreseeable potential in the applications of high-power/temperature electronics, andoptoelectronic devices operative in UV and visible wavelength. Polarization inducedelectric field can reach the magnitude of ~MV/cm[1,2]. For AlGaN/GaN based FETs theconcentration of sheet carrier induced by polarization in the cha…     

Simulation study of InAlN/GaN high-electron mobility transistor with AlInN back barrier

In this work, we use a 3-nm-thick Al_(0.64)In_(0.36)N back-barrier layer in In_(0.17)Al_(0.83) N/Ga N high-electron mobility transistor(HEMT) to enhance electron confinement. Based on two-dimensional device simulations, the influences of Al_(0.64)In_(0.36) N back-barrier on the direct-current(DC) and radio-frequency(RF) characteristics of In AlN/GaN HEMT are investigated, theoretically. It is shown that an effective conduction band discontinuity of approximately 0.5 eV is created by the 3-nm-thick Al_(0.64)In_(0.36) N back-barrier and no parasitic electron channel is formed. Comparing with the conventional In AlN/GaN HEMT, the electron confinement of the back-barrier HEMT is significantly improved, which allows a good immunity to short-channel effect(SCE) for gate length decreasing down to 60 nm(9-nm top barrier). For a 70-nm gate length, the peak current gain cut-off frequency( f_T) and power gain cut-off frequency( f_(max)) of the back-barrier HEMT are172 GHz and 217 GHz, respectively, which are higher than those of the conventional HEMT with the same gate length.     

Impact of dopants in GaN on the formation of two-dimensional electron gas in AlGaN/GaN heterostructure field-effect transistors

The two-dimensional electron gas distribution in AlGaN/GaN high electron mobility transistors is determined from the solution of the coupled Schr?dinger’s and Poisson’s equations. Considering the piezoelectric effect, the two-dimensional electron gas concentration is calculated to be as high as 7.7×10¹⁹ cm^-3. In order to obtain an understanding of how the two-dimensional electron gas distribution is influenced by dopants in GaN, we observed the two-dimensional electron gas concentration and occupation of sub-bands versus dopant concentration in the GaN layer of an AlGaN/GaN heterostructure. Our results show that the two-dimensional electron gas concentration is slightly increased at higher doping levels in GaN, while the quantum confinement in the AlGaN/GaN heterostructure is weakened with the increase of donor concentration in the GaN layer. Received: 26 May 2001 / Accepted: 23 July 2001 / Published online: 23 January 2002     

AlGaN/GaN双异质结F注入增强型高电子迁移率晶体管

理论模拟了不同GaN沟道厚度的双异质结(AlGaN/GaN/AlGaN/GaN)材料对高电子迁移率晶体管(HEMT)特性的影响,并模拟了不同F注入剂量下用该材料制作的增强型器件的特性差异.采用双异质结材料,结合F注入工艺成功地研制出了较高正向阈值电压的增强型HEMT器件.实验研究了三种GaN沟道厚度制作的增强型器件直流特性的差异,与模拟结果进行了对比验证.采用降低的F注入等离子体功率,减小了等离子体处理工艺对器件沟道迁移率的损伤,研制出的器件未经高温退火即实现了较高的跨导和饱和电流特性.对14 nm GaN沟道厚度的器件进行了阈值电压温度稳定性和栅泄漏电流的比较研究,并且分析了双异质结器件的漏致势垒降低效应.