转移基板材质对Si衬底GaN基LED芯片性能的影响

在Si衬底上生长了GaN基LED外延材料,分别转移到新的硅基板和铜基板上,制备了垂直结构蓝光LED芯片。研究了这两种基板GaN基LED芯片的光电性能。在切割成单个芯片之前,对大量尺寸为(300μm×300μm)的这两种芯片分别通高达1 A的大电流在测试台上加速老化1 h。结果显示,铜基板Si衬底GaN基LED芯片有更大的饱和电流,光输出效率更高,工作电压随驱动电流的变化不大,光输出在老化过程中衰减更小。铜基板芯片比硅基板芯片可靠性更高,在大功率半导体照明器件中前景诱人。     

Growth by molecular beam epitaxy of AlGaN/GaN high electron mobility transistors on Si-on-polySiC

We report on the growth by molecular beam epitaxy of AlGaN/GaN high electron mobility transistors (HEMTs) on Si(111)/ SiO₂/polySiC substrates. The structural, optical, and electrical properties of these films are studied and compared with those of heterostructures grown on thick Si(111) substrates. Field effect transistors have been realized, and they demonstrate the potentialities of III–V nitrides grown on these advanced substrates.     

基于拉曼热测量技术的铜基复合物法兰GaN基晶体管的热阻分析

采用拉曼热测量技术结合有限元热仿真模型,分析比较新型铜/石墨复合物法兰封装与传统铜钼法兰封装的GaN器件的结温与热阻,发现前者的整体热阻比铜钼法兰器件的整体热阻低18.7%,器件内部各层材料的温度分布显示铜/石墨复合物法兰在器件中的热阻占比相比铜钼法兰在器件中的热阻占比低13%,这证明使用高热导率铜/石墨复合物法兰封装提高GaN器件热扩散性能的有效性.通过对两种GaN器件热阻占比的测量与分析,发现除了封装法兰以外,热阻占比最高的是GaN外延与衬底材料之间的界面热阻,降低界面热阻是进一步提高器件热性能的关键.同时,详细阐述了使用拉曼光热技术测量GaN器件结温和热阻的原理和过程,展示了拉曼光热技术作为一种GaN器件热特性表征方法的有效性.     

High vertical breakdown strength in with low specific on‐resistance AlGaN/AlN/GaN HEMTs on silicon

Off‐state and vertical breakdown characteristics of AlGaN/AlN/GaN high‐electron‐mobility transistors (HEMTs) on high‐resistivity (HR)‐Si substrate were investigated and analysed. Three‐terminal off‐state breakdown (BV_gd) was measured as a function of gate–drain spacing (L_gd). The saturation of BV_gd with L_gd is because of increased gate leakage current. HEMTs with L_gd = 6 µm exhibited a specific on‐resistance R_DS[ON] of 0.45 mΩ cm². The figure of merit (FOM = BV_gd²/R_DS[ON]) is as high as 2.0 × 10⁸ V² Ω^–1 cm^–2, the highest among the reported values for GaN HEMTs on Si substrate. A vertical breakdown of ～1000 V was observed on 1.2 µm thick buffer GaN/AlN grown on Si substrate. The occurrence of high breakdown voltage is due to the high quality of GaN/AlN buffer layers on Si substrate with reduced threading dislocations which has been confirmed by transmission electron microscopy (TEM). This indicates that the AlGaN/AlN/GaN HEMT with 1.2 µm thick GaN/AlN buffer on Si substrate is promising candidate for high‐power and high‐speed switching device applications. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Plasma Etching in InAlN/GaN Hemt Technology

Russian Physics Journal - The experimental data on the plasma etching of Si3N4 for sub-100 nm gate fabrication for high electron mobility transistors (HEMTs) based on InAlN/GaN heterostructures are...     

Si衬底GaN基LED外延薄膜转移至金属基板的应力变化

采用电镀金属基板及湿法腐蚀衬底的方法将硅衬底上外延生长的GaNMQWLED薄膜转移至不同结构的金属基板,通过高分辨X射线衍射(HRXRD)和光致发光(PL)研究了转移的GaN薄膜应力变化。研究发现:(1)转移至铜基板、铬基板、铜/镍/铜叠层基板等三种基板的GaN薄膜张应力均减小,其中转移至铬基板的GaN薄膜张应力最小。(2)随着铬基板中铬主体层厚度的增加,转移后的GaN薄膜应力不发生明显变化。     

Effect of SiN:H_x passivation layer on the reverse gate leakage current in GaN HEMTs

This paper concentrates on the impact of SiN passivation layer deposited by plasma-enhanced chemical vapor deposition(PECVD) on the Schottky characteristics in GaN high electron mobility transistors(HEMTs). Three types of SiN layers with different deposition conditions were deposited on GaN HEMTs. Atomic force microscope(AFM), capacitance-voltage(C-V), and Fourier transform infrared(FTIR) measurement were used to analyze the surface morphology, the electrical characterization, and the chemical bonding of SiN thin films, respectively. The better surface morphology was achieved from the device with lower gate leakage current. The fixed positive charge Q_f was extracted from C-V curves of Al/SiN/Si structures and quite different density of trap states(in the order of magnitude of 1011-1012 cm~(-2)) was observed.It was found that the least trap states were in accordance with the lowest gate leakage current. Furthermore, the chemical bonds and the %H in Si-H and N-H were figured from FTIR measurement, demonstrating an increase in the density of Q_f with the increasing %H in N-H. It reveals that the effect of SiN passivation can be improved in GaN-based HEMTs by modulating %H in Si-H and N-H, thus achieving a better Schottky characteristics.     

高阻GaN的MOCVD外延生长

利用金属有机化合物气相沉积(MOCVD)在蓝宝石衬底上生长了高阻GaN薄膜。对GaN成核层生长的反应室压力、生长时间和载气类型对GaN缓冲层电学特性的影响进行了分析。实验结果表明,延长GaN成核层的生长时间,降低成核层生长时的反应室压力,载气由H₂换为N₂都会得到高阻的GaN缓冲层。样品的方块电阻R_s最高为2.49×10¹¹ Ω/□。以高阻GaN样品为衬底制备了AlGaN/AlN/GaN结构HEMT器件,迁移率最高达1 230 cm²/(V·s)。     

Fabrication and characterization of V-gate AlGaN/GaN high-electron-mobility transistors

V-gate GaN high-electron-mobility transistors (HEMTs) are fabricated and investigated systematically. A V-shaped recess geometry is obtained using an improved Si3N4 recess etching technology. Compared with standard HEMTs, the fabricated V-gate HEMTs exhibit a 17% higher peak extrinsic transconductance due to a narrowed gate foot. Moreover, both the gate leakage and current dispersion are dramatically suppressed simultaneously, although a slight degradation of frequency response is observed. Based on a two-dimensional electric field simulation using Silvaco "ATLAS" for both standard HEMTs and V-gate HEMTs, the relaxation in peak electric field at the gate edge is identified as the predominant factor leading to the superior performance of V-gate HEMTs.     

Si衬底GaN基LED的结温特性

结温是发光二极管的重要参数之一,它对器件的内量子效率、输出功率、可靠性及LED的其他一些性能有很大的影响。首次报道Si衬底GaN基LED的结温特性。利用正向压降法测量Si衬底上GaN基LED的结温,通过与蓝宝石衬底上GaNLED的结温比较,发现Si衬底GaNLED有更低的结温,原因归结为Si有更好的导热性。同时也表明:用Si作GaNLED的衬底在大功率LED方面具有更大的应用潜力。     

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.     

GaN epilayers on nanopatterned GaN/Si(1 1 1) templates: Structural and optical characterization

Template-based nanoscale epitaxy has been explored to realize high-quality GaN on Si(1 1 1) substrates. We have employed polystyrene-based nanosphere lithography to form the nano-hole array patterns on GaN/Si(1 1 1) template and then, subsequent regrowth of GaN is carried out by metalorganic chemical vapor deposition (MOCVD). During the initial growth stage of GaN on such nanopatterned substrates, we have observed formation of nanoislands with hexagonal pyramid shape due to selective area epitaxy. With further epitaxial regrowth, these nanoislands coalesce and form continuous GaN film. The overgrown GaN on patterned and non-patterned regions is characterized by high-resolution X-ray diffraction (HRXRD) and high-spatial resolution optical spectroscopic methods. Micro-photoluminescence (PL), micro-Raman scattering and scanning electron microscopy (SEM) have been used to assess the microstructural and optical properties of GaN. Combined PL and Raman data analyses show improved optical quality when compared to GaN simultaneously grown on non-patterned bulk Si(1 1 1). Such thicker GaN templates would be useful to achieve III-nitride-based opto- and electronic devices integrated on Si substrates.     

Heteroepitaxial GaN films on silicon substrates with porous buffer layers

New complex buffer layers based on a porous material have been developed for epitaxial growth of GaN films on Si substrates. The characteristics of gallium nitride heteroepitaxial layers grown on silicon substrates with new buffer layers by metal-organic vapor phase epitaxy are investigated. It is shown that the porous buffer layers improve the electric homogeneity and increase the photoluminescence intensity of epitaxial GaN films on Si substrates to the values comparable with those for reference GaN films on Al₂O₃ substrates. It is found that a fianite layer in a complex buffer is a barrier for silicon diffusion from the substrate into a GaN film.     

The effects of ⁶⁰Co γ-ray irradiation on the DC characteristics of enhancement-mode AlGaN/GaN high-electron-mobility transistors

The effects of 60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electron-mobility transistors (E-mode HEMTs) are investigated. The results show that having been irradiated by 60Co γ-rays at a dose of 3 Mrad (Si), the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode AlGaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.     

阶梯AlGaN外延新型Al_(0.25)Ga_(0.75)N/GaNHEMTs击穿特性分析

为了优化AlGaN/GaN HEMTs器件表面电场,提高击穿电压,本文首次提出了一种新型阶梯AlGaN/GaN HEMTs结构.新结构利用AlGaN/GaN异质结形成的2DEG浓度随外延AlGaN层厚度降低而减小的规律,通过减薄靠近栅边缘外延的AlGaN层,使沟道2DEG浓度分区,形成栅边缘低浓度2DEG区,低的2DEG使阶梯AlGaN交界出现新的电场峰,新电场峰的出现有效降低了栅边缘的高峰电场,优化了AlGaN/GaN HEMTs器件的表面电场分布,使器件击穿电压从传统结构的446 V,提高到新结构的640 V.为了获得与实际测试结果一致的击穿曲线,本文在GaN缓冲层中设定了一定浓度的受主型缺陷,通过仿真分析验证了国际上外延GaN缓冲层时掺入受主型离子的原因,并通过仿真分析获得了与实际测试结果一致的击穿曲线.     

Effects of SiNx on two-dimensional electron gas and current collapse of AlGaN/GaN high electron mobility transistors

SiN_x is commonly used as a passivation material for AlGaN/GaN high electron mobility transistors (HEMTs). In this paper, the effects of SiN_x passivation film on both two-dimensional electron gas characteristics and current collapse of AlGaN/GaN HEMTs are investigated. The SiN_x films are deposited by high- and low-frequency plasma-enhanced chemical vapour deposition, and they display different strains on the AlGaN/GaN heterostructure, which can explain the experiment results.     

The effects of 60Co γ-ray irradiation on the DC characteristics of enhancement-mode AlGaN/GaN high-electron-mobility transistors

The effects of 60Co γ-ray irradiation on the DC characteristics of AlGaN/GaN enhancement-mode high-electron-mobility transistors (E-mode HEMTs) are investigated. The results show that having been irradiated by 60Co γ-rays at a dose of 3 Mrad (Si), the E-mode HEMT reduces its saturation drain current and maximal transconductance by 6% and 5%, respectively, and significantly increases both forward and reverse gate currents, while its threshold voltage is affected only slightly. The obvious performance degradation of E-mode AlGaN/GaN HEMTs is consistent with the creation of electronegative surface state charges in the source-gate spacer and gate-drain spacer after being irradiated.     

Simulation design of normally-off AlGaN/GaN high-electron-mobility transistors with p-GaN Schottky hybrid gate

A novel normally-off AlGaN/GaN high-electron-mobility transistor (HEMT) with a p-GaN Schottky hybrid gate (PSHG) is proposed, and compared with the conventional p-GaN normally-off AlGaN/GaN HEMTs. This structure can be realized by selective etching of p-GaN layer, which enables the Schottky junction and PN junction to control the channel charge at the same time. The direct current (DC) and switching characteristics of the PSHG HEMTs are simulated by Slivaco TCAD, and the p-GaN HEMTs and conventional normally-on HEMTs are also simulated for comparison. The simulation results show that the PSHG HEMTs have a higher current density and a lower on-resistance than p-GaN HEMTs, which is more obvious with the decrease of p-GaN ratios of the PSHG HEMTs. The breakdown voltage and threshold voltage of the PSHG HEMTs are very close to those of the p-GaN HEMTs. In addition, the PSHG HEMTs have a higher switching speed than the conventional normally-on HEMTs, and the p-GaN layer ratio has no obvious effect on the switching speed.     

硅衬底氮化镓基LED薄膜转移至柔性黏结层基板后其应力及发光性能变化的研究

本文将硅(Si)衬底上外延生长的氮化镓(GaN)基发光二极管(LED)薄膜转移至含有柔性黏结层的基板上, 获得了不受衬底和支撑基板束缚的LED薄膜. 利用高分辨率X射线衍射仪(HRXRD)研究了薄膜转移前后的应力变化, 同时对其光致发光(PL)光谱的特性进行了研究. 结果表明: 硅衬底GaN基LED薄膜转移至柔性基板后, GaN受到的应力会由转移前巨大的张应力变为转移后微小的压应力, InGaN/GaN量子阱受到的压应力则增大; 尽管LED薄膜室温无损转移至柔性基板其InGaN阱层的In组分不会改变, 然而按照HRXRD倒易空间图谱通用计算方法会得出平均铟组发生了变化; GaN基LED薄膜从外延片转移至柔性基板时其PL谱会发生明显红移.     

基于GaN同质衬底的高迁移率AlGaN/GaNHEMT材料

研究了表面预处理对GaN同质外延的影响,获得了高电子迁移率AlGaN/GaN异质结材料.通过NH_3/H_2混合气体与H_2交替通入反应室的方法对GaN模板和GaN半绝缘衬底进行高温预处理.研究结果表明,NH_3/H_2能够抑制GaN的分解,避免粗糙表面,但不利于去除表面的杂质,黄光带峰相对强度较高;H_2促进GaN分解,随时间延长GaN分解加剧,导致模板表面粗糙不平,AlGaN/GaN HEMT材料二维电子气迁移率降低.采用NH_3/H_2混合气体与H_2交替气氛模式处理模板或衬底表面,能够清洁表面,去除表面杂质,获得平滑的生长表面和外延材料表面,有利于提高AlGaN/GaN HEMT材料电学性能.在GaN衬底上外延AlGaN/GaN HEMT材料,2DEG迁移率达到2113 cm~2/V·s,电学性能良好.