用于GaN CMOS集成技术的p型GaN欧姆接触研究

通过金属叠层结构、蒸发-合金工艺条件的优化调整,实现了低接触电阻率、高稳定的p型GaN欧姆接触技术,并研究分析了电极金属在合金过程中的扩散行为。测试结果显示,改进后的p型GaN欧姆接触电阻为11.9Ω·mm,比导通电阻率为3.9×10^(-5)Ω·cm^(2),同时在250℃以内的高温环境中欧姆特性不会发生退化。在此基础上,采用低损伤凹槽栅刻蚀、叠层栅介质沉积等工艺研制出增强型p沟道GaN晶体管器件,器件的阈值电压为-1.2 V(V_(GS)=VDS,IDS=10μA/mm),漏极电流密度为-5.6 mA/mm,导通电阻为665Ω·mm(V_(GS)=-8 V,V_(DS)=-2 V)。优异的p型GaN欧姆接触技术为高性能GaN p沟道器件的研制以及GaN CMOS集成技术的小型化、智能化、高速化发展奠定了重要基础。

融合门控变换机制和GAN的低光照图像增强方法

针对低光照图像增强过程中存在的配对图像数据依赖、细节损失严重和噪声放大问题,提出结合门控通道变换机制和生成对抗网络(GAN)的低光照图像增强方法AGR-GAN,该方法可以在没有低/正常光图像对的情况下进行训练。首先,设计特征提取网络,该网络由多个基于门控通道变换单元的多尺度卷积残差模块构成,以提取输入图像的全局上下文特征和多尺度局部特征信息;然后,在特征融合网络中,采用卷积残差结构将提取的深浅层特征进行充分融合,再引入横向跳跃连接结构,最大程度保留细节特征信息,获得最终的增强图像;最后,引入联合损失函数指导网络训练过程,抑制图像噪声,使增强图像色彩更自然匀称。实验结果表明,该方法在主观视觉分析和客观指标评价方面相较其他算法均具有显著优势,其能有效提高低光照图像的亮度和对比度,减弱图像噪声,增强后的图像更清晰且色彩更真实,峰值信噪比、结构相似度和无参考图像质量评价指标平均可达16.48 dB、0.93和3.37。

基于微区拉曼法的AlGaN/GaN HEMT沟道温度测试研究

针对现有温度测试技术难以满足GaN器件寿命、可靠性以及热管理控制对沟道温度精确评估的需求,开展基于微区拉曼法测定AlGaN/GaN高电子迁移率晶体管(HEMT)的沟道温度的研究。使用拉曼系统测量GaN材料的E2声子频率特征峰来确定沟道温度。通过使用洛伦兹拟合方法,提高拉曼测试结果精度。对微区拉曼法和红外热成像法测量器件结温进行量化研究,器件的直流输出功率密度分别为6、8、10 W/mm时基于微区拉曼法测得的GaN器件沟道温度分布为140.7、176.7、213.6℃;基于红外热成像法测得的温度分布为132.0、160.2、189.8℃。其测试精度相对红外法分别提升6.6%,10.3%和12.5%,同时尝试探索沟道深度方向的温度测量,实现沟道下3μm的温度测量,结果表明微区拉曼法有更高的测试精度,对器件结温的测量与评估以及热管理技术的提升都有重要意义。

MMIC LNA based novel composite-channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMTs

A microwave monolithic integrated circuit （MMIC） C-band low noise amplifier （LNA） using 1 μm-gate composite-channel Al0.3Ga0.7N/Al0.05Ga0.95N/GaN high electron mobility transistors （CC-HEMTs） has been designed, fabricated and characterized. The material structure and special channel of CC-HEMT were given and analysed. The MMIC LNA with CC-HEMT showed a noise figure of 2.4 dB, an associated gain of 12.3 dB, an input return loss of -6 dB and an output return loss of -16 dB at 6GHz. The IIP3 of the LNA is 13 dBm at 6 GHz. The LNA with 1 μm ×100 μm device showed very high-dynamic range with decent gain and noise figure.

Breakdown voltage enhancement in GaN channel and AlGaN channel HEMTs using large gate metal height

A large gate metal height technique is proposed to enhance breakdown voltage in GaN channel and AlGaN channel high-electron-mobility-transistors(HEMTs).For GaN channel HEMTs with gate-drain spacing LGD=2.5μm,the breakdown voltage VBR increases from 518 V to 582 V by increasing gate metal height h from 0.2μm to 0.4μm.For GaN channel HEMTs with LGD=7μm,VBR increases from 953 V to 1310 V by increasing h from 0.8μm to 1.6μm.The breakdown voltage enhancement results from the increase of the gate sidewall capacitance and depletion region extension.For Al0.4Ga0.6N channel HEMT with LGD=7μm,VBR increases from 1535 V to 1763 V by increasing h from 0.8μm to 1.6μm,resulting in a high average breakdown electric field of 2.51 MV/cm.Simulation and analysis indicate that the high gate metal height is an effective method to enhance breakdown voltage in GaN-based HEMTs,and this method can be utilized in all the lateral semiconductor devices.

Breakdown mechanisms in AlGaN/GaN high electron mobility transistors with different GaN channel thickness values

In this paper,the off-state breakdown characteristics of two different AlGaN/GaN high electron mobility transistors（HEMTs）,featuring a 50-nm and a 150-nm GaN thick channel layer,respectively,are compared.The HEMT with a thick channel exhibits a little larger pinch-off drain current but significantly enhanced off-state breakdown voltage（SVoff）.Device simulation indicates that thickening the channel increases the drain-induced barrier lowering（DIBL） but reduces the lateral electric field in the channel and buffer underneath the gate.The increase of BVoff in the thick channel device is due to the reduction of the electric field.These results demonstrate that it is necessary to select an appropriate channel thickness to balance DIBL and BVoff in AlGaN/GaN HEMTs.

Groove-type channel enhancement-mode Al GaN/GaN MIS HEMT with combined polar and nonpolar AlGaN/GaN heterostructures

A novel groove-type channel enhancement-mode AlGaN/GaN MIS high electron mobility transistor（GTCE-HEMT）with a combined polar and nonpolar AlGaN/GaN heterostucture is presented. The device simulation shows a threshold voltage of 1.24 V, peak transconductance of 182 m S/mm, and subthreshold slope of 85 m V/dec, which are obtained by adjusting the device parameters. Interestingly, it is possible to control the threshold voltage accurately without precisely controlling the etching depth in fabrication by adopting this structure. Besides, the breakdown voltage（VB） is significantly increased by 78% in comparison with the value of the conventional MIS-HEMT. Moreover, the fabrication process of the novel device is entirely compatible with that of the conventional depletion-mode（D-mode） polar AlGaN/GaN HEMT. It presents a promising way to realize the switch application and the E/D-mode logic circuits.

Enhancement-Mode AlGaN/GaN High Electron Mobility Transistors Using a Nano-Channel Array Structure

A nano-channel array(NCA)structure is applied to realize enhancement-mode(E-mode)AlGaN/GaN high-electron mobility transistors(HEMTs).The fabricated NCA-HEMT,consisting of 1000 channels connected in parallel with a channel width of 64 nm,shows a threshold voltage of 0.15 V and a subthreshold slope of 78 mV/dec,compared to−3.92 V and 99 mV/dec for a conventional HEMT(C-HEMT),respectively.Both the NCA-HEMT and C-HEMT show similar gate leakage current,indicating no significant degradation in gate leakage characteristics for the NCA-HEMT.The surrounding-field effect and relieved polarization contribute to the very large positive threshold voltage shift,while the work function difference makes it positive.

Influence of the channel electric field distribution on the polarization Coulomb field scattering in In_(0.18) Al_(0.82) N/AlN/GaN heterostructure field-effect transistors

By making use of the quasi-two-dimensional （quasi-2D） model, the current-voltage （l-V） characteristics of In0AsA10.82N/A1N/GaN heterostructure field-effect transistors （HFETs） with different gate lengths are simulated based on the measured capacitance-voltage （C-V） characteristics and I-V characteristics. By analyzing the variation of the electron mobility for the two-dimensional electron gas （2DEG） with electric field, it is found that the different polarization charge distributions generated by the different channel electric field distributions can result in different polarization Coulomb field scatterings. The difference between the electron mobilities primarily caused by the polarization Coulomb field scatterings can reach up to 1522.9 cm2/V.s for the prepared In0.38AI0.82N/A1N/GaN HFETs. In addition, when the 2DEG sheet density is modulated by the drain-source bias, the electron mobility presents a peak with the variation of the 2DEG sheet density, the gate length is smaller, and the 2DEG sheet density corresponding to the peak point is higher.

Trap analysis of composite 2D-3D channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C multi-heterostructure at different temperatures

The graded AlGaN:Si back barrier can form the majority of three-dimensional electron gases(3DEGs)at the GaN/graded AlGaN:Si heterostructure and create a composite two-dimensional(2D)-three-dimensional(3D)channel in AlGaN/GaN/graded-AlGaN:Si/GaN:C heterostructure(DH:Si/C).Frequency-dependent capacitances and conductance are measured to investigate the characteristics of the multi-temperature trap states of in DH:Si/C and AlGaN/GaN/GaN:C heterostructure(SH:C).There are fast,medium,and slow trap states in DH:Si/C,while only medium trap states exist in SH:C.The time constant/trap density for medium trap state in SH:C heterostructure are(11μs-17.7μs)/(1.1×10^13 cm^-2·eV^-1-3.9×10^13 cm^-2·eV^-1)and(8.7μs-14.1μs)/(0.7×10^13 cm^-2·eV^-1-1.9×10^13 cm^-2·eV^-1)at 300 K and 500 K respectively.The time constant/trap density for fast,medium,and slow trap states in DH:Si/C heterostructure are(4.2μs-7.7μs)/(1.5×10^13 cm^-2·eV^-1-3.2×10^13 cm^-2·eV^-1),(6.8μs-11.8μs)/(0.8×10^13 cm^-2·eV^-1-2.8×10^13 cm^-2·eV^-1),(30.1μs-151μs)/(7.5×10^12 cm^-2·eV^-1-7.8×10^12 cm^-2·eV^-1)at 300 K and(3.5μs-6.5μs)/(0.9×10^13 cm^-2·eV^-1-1.8×10^13 cm^-2·eV^-1),(4.9μs-9.4μs)/(0.6×10^13 cm^-2·eV^-1-1.7×10^13 cm^-2·eV^-1),(20.6μs-61.9μs)/(3.2×10^12 cm^-2·eV^-1-3.5×10^12 cm^-2·eV^-1)at 500 K,respectively.The DH:Si/C structure can effectively reduce the density of medium trap states compared with SH:C structure.

An Al0.25Ga0.75N/GaN Lateral Field Emission Device with a Nano Void Channel

We report an Al0.25Ga0.75N/GaN based lateral field emission device with a nanometer scale void channel. A -45 nm void channel is obtained by etching out the SiO2 sacrificial dielectric layer between the semiconductor emitter and the metal collector. Under an atmospheric environment instead of vacuum conditions, the OaN- based field emission device shows a low turn-on voltage of 2.3 V, a high emission current of -40 μA （line current density 2.3mA/cm） at a collector bias Vc = 3 V, and a low reverse leakage of 3nA at Vc = -3 V. These characteristics are attributed to the nanometer scale void channel as well as the high density of two-dimensional electron gas in the AlGaN/GaN heterojunction. This type of device may have potential applications in high frequency mieroelectronics or nanoelectronics.

AlGaN Channel High Electron Mobility Transistors with an AlxGa1-xN/GaN Composite Buffer Layer

We report an AlGaN channel high electron mobility transistor （HEMT） on a sapphire substrate with a 1000-nm A1xGa1-xN （x = 0-0.18）/GaN composite buffer layer, With a significant improvement of crystal quality, the device features a high product orris. #n. The AIGaN channel HEMTs presented show improved performance with respect to the conventional AIGaN channel HEMTs, including the on-resistance reduced from 31.2 to 8.1 Ω.mm, saturation drain current at 2 V gate bias promoted from 218 to 540 mA/mm, peak transconductance at 10 V drain bias promoted from 100 to a state-of-the-art value of 174 mS/ram, and reverse gate leakage current reduced from 1.85 × 10-3 to 2.15 × 10-5 mA/mm at VOD = -20 V.

Strain in GaN/Si<111> by RBS/Channeling

GaN film grown on Si substrate was characterized by Rutherford backscattering/Channeling (RBS/C). The experimental results show that the thick- ness of GaN epilayer is about 2.5 μm and the GaN film has a good crystalline quality (Xmin=3.3%). By using channeling angular scanning. the 0.35% of average tetragonal distortion in GaN layer is observed. In addition, the depth profiles of strain in GaN film layer reveal that the strain in GaN film nonlinearly decreases with the increase of film thickness. The strain-free thickness (above 2.5 μm) of GaN film on Si substrate is far below that (150μm) of GaN film on Sapphire.

新型再生长沟道GaN基准垂直MOSFET仿真研究

电能在转化与运用过程中会不可避免地出现能量的损耗,而电力控制和电能转换过程中最核心部分即为电力电子器件。GaN基准垂直MOSFET器件具有高输入阻抗、开关速率快以及对表面态陷阱不太敏感等优点,从而成为目前研究的热点,但由于沟道载流子的迁移率较低造成导通电阻与损耗较大。通过对再生长沟道GaN基准垂直MOSFET进行仿真,证明该结构可以有效解决沟道载流子的迁移率过低的问题。在再生长沟道GaN基准垂直MOSFET的基础上进行了结构改进,主要针对器件在源极区域与漂移区域的载流子分布进行了优化。其中,源极区域通过对源电极金属帽子下方Al_(2)O_(3)进行刻蚀,使得器件源极区域的电流导通路径得到了有效的缩短;而漂移区域通过在栅极下方插入一层载流子分布层,使得漂移区内载流子分布更加均匀。最终设计出了阈值电压为2.3V的新型再生长沟道GaN基准垂直MOSFET,器件的导通电阻低至1.8mΩ·cm^(2),击穿电压高达1053V。

A review on GaN HEMTs:nonlinear mechanisms and improvement methods

The GaN HEMT is a potential candidate for RF applications due to the high frequency and large power handling capability.To ensure the quality of the communication signal,linearity is a key parameter during the system design.However,the GaN HEMT usually suffers from the nonlinearity problems induced by the nonlinear parasitic capacitance,transconductance,channel transconductance etc.Among them,the transconductance reduction is the main contributor for the nonlinearity and is mostly attributed to the scattering effect,the increasing resistance of access region,the self-heating effect and the trapping effects.Based on the mechanisms,device-level improvement methods of transconductance including the trapping suppression,the nanowire channel,the graded channel,the double channel,the transconductance compensation and the new material structures have been proposed recently.The features of each method are reviewed and compared to provide an overview perspective on the linearity of the GaN HEMT at the device level.

High threshold voltage enhancement-mode GaN p-FET with Sirich LPCVD SiN_(x) gate insulator for high hole mobility

In this work,the GaN p-MISFET with LPCVD-SiN_(x) is studied as a gate dielectric to improve device performance.By changing the Si/N stoichiometry of SiN_(x),it is found that the channel hole mobility can be effectively enhanced with Si-rich SiN_(x) gate dielectric,which leads to a respectably improved drive current of GaN p-FET.The record high channel mobility of 19.4 cm2/(V∙s)was achieved in the device featuring an Enhancement-mode channel.Benefiting from the significantly improved channel mobility,the fabricated E-mode GaN p-MISFET is capable of delivering a decent-high current of 1.6 mA/mm,while simultaneously featuring a negative threshold-voltage(VTH)of–2.3 V(defining at a stringent criteria of 10μA/mm).The device also exhibits a well pinch-off at 0 V with low leakage current of 1 nA/mm.This suggests that a decent E-mode operation of the fabricated p-FET is obtained.In addition,the VTH shows excellent stability,while the threshold-voltage hysteresisΔVTH is as small as 0.1 V for a gate voltage swing up to–10 V,which is among the best results reported in the literature.The results indicate that optimizing the Si/N stoichiometry of LPCVD-SiN_(x) is a promising approach to improve the device performance of GaN p-MISFET.

Analytical model of non-uniform charge distribution within the gated region of GaN HEMTs

A physics-based analytical expression that predicts the charge,electrical field and potential distributions along the gated region of the GaN HEMT channel has been developed.Unlike the gradual channel approximation(GCA),the proposed model considers the non-uniform variation of the concentration under the gated region as a function of terminal applied volt-ages.In addition,the model can capture the influence of mobility and channel temperature on the charge distribution trend.The comparison with the hydrodynamic(HD)numerical simulation showed a high agreement of the proposed model with numerical data for different bias conditions considering the self-heating and quantization of the electron concentration.The ana-lytical nature of the model allows us to reduce the computational and time cost of the simulation.Also,it can be used as a core expression to develop a complete physics-based transistorⅣmodel without GCA limitation.

AlN/GaN HEMT毫米波器件结构仿真研究

为实现更高工作频率的氮化镓(gallium nitride,GaN)基高电子迁移率晶体管(high electron mobility transistor,HEMT)器件,采用薄势垒外延结构、缩小栅长对提升器件的截止频率十分重要。通过对不同氮化铝(aluminium nitride,AIN)势垒层厚度以及不同尺寸栅长的AlN/GaN HEMT进行仿真分析,系统研究不同结构对器件短沟道效应、直流及频率等特性的影响。首先固定栅长为100nm,研究了跨导与截止频率随AlN势垒层厚度的变化情况。跨导随势垒层厚度的增加先增大后减小。当势垒层厚度为4nm时,跨导达到最大值(592mS/mm),截止频率也达到最大值。为尽可能提升器件的截止频率,同时避免器件出现短沟道效应,固定AlN势垒层厚度为4nm,研究器件截止频率与短沟道效应随器件栅长的变化情况。仿真表明器件截止频率随栅长的减小而增大,50nm栅长的器件截止频率最高,但栅长为50nm时器件短沟道效应严重,此时器件纵横比(L_(g)/T_(bar))为12.5。因此需要提升器件的纵横比,当器件栅长达到100nm时(L_(g)/T_(bar)=25),器件短沟道效应得到抑制,且具有较高的截止频率。仿真结果表明,AlN HEMT具有较高的截止频率,同时应采用较大的纵横比设计(纵横比为25左右)以抑制短沟道效应,为后续高频AlN/GaN HEMTs器件的制备提供了理论依据。

基于应变迁移率模型对应变沟道AlGaN/GaNHEMT器件电子输运特性的研究

为了进一步提升AlGaN/GaN HEMTs的电流特性,提出了一种在非栅下沟道插入InGaN弛豫层的应变GaN沟道AlGaN/5-nm-GaN/InGaN HEMT(SGC-HEMT)器件结构。通过Sentaurus TCAD仿真研究了SGC-HEMT器件电子输运特性。基于修正的应变迁移率模型,通过改变InGaN弛豫层的In组分调整沟道应变的大小,同时考虑了5-nm-GaN沟道应变和AlGaN势垒层的附加应变,讨论了极化诱导电子气分布与沟道应变的理论关系。仿真结果表明,应变的引入显著增加了器件的漏极饱和电流,当In组分为0.02时,应变GaN(GaNs)沟道层和AlGaN势垒层的拉伸应变为0.225%,SGC-HEMT的漏极饱和电流为0.914 A·mm^(-1),相比传统GaN/AlGaN HEMT的0.701 A·mm^(-1)提高了30.63%;随着沟道拉伸应变的进一步施加,散射机制不断增强,漏极饱和电流和有效迁移率的增长趋于平缓,栅极泄漏也逐渐恶化。此外,由于栅极下方的沟道未施加应变,阈值电压基本不随应变而变化。最后,提取了不同拉伸应变下的有效迁移率,发现随着沟道拉伸应变的增加,低电场区的有效迁移率较高,而高电场区的衰减较慢。对应变沟道GaN HEMT电子输运特性的研究成果有利于进一步提高AlGaN/GaN HEMT的电学性能。

GaN的RBS/沟道、X射线双晶衍射和光致发光谱

采用卢瑟福背散射及沟道效应、X射线双晶衍射和光致发光谱三种技术对两类未故意掺杂的 MOVPE生长的 Ga N样品进行综合测试 .它们在表征 Ga