AlGaN/GaN肖特基结参数分析与电流运输机理研究

通过对AlGaN/GaN HEMT器件肖特基栅电流输运机理的研究,在变温下采用I-V法对AlGaN/GaN上的Ni/Au肖特基势垒高度和理想因子进行了计算. 通过对不同电流机理的分立研究,得到了更为准确的势垒高度值_b. 通过分析温度在300—550K之间肖特基反向泄漏电流的特性,得出结论：AlGaN材料的表面漏电不是HEMT器件反向泄漏电流的主要来源. 关键词： AlGaN/GaN异质结 肖特基结 理想因子     

SILC during NBTI Stress in PMOSFETs with Ultra-Thin SiON Gate Dielectrics

Negative bias temperature instability （NBTI） and stress-induced leakage current （SILC） both are more serious due to the aggressive scaling lowering of devices. We investigate the SILC during NBTI stress in PMOSFETs with ultra-thin gate dielectrics. The SILC sensed range from -1 V to 1 V is divided into four parts： the on-state SILC, the near-zero SILC, the off-state SILC sensed at lower positive voltages and the one sensed at higher positive voltages. We develop a model of tunnelling assisted by interface states and oxide bulk traps to explain the four different parts of SILC during NBTI stress.     

Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transistor with SiN passivation

The transport mechanism of reverse surface leakage current in the AlGaN/GaN high-electron mobility transistor(HEMT) becomes one of the most important reliability issues with the downscaling of feature size.In this paper,the research results show that the reverse surface leakage current in AlGaN/GaN HEMT with SiN passivation increases with the enhancement of temperature in the range from 298 K to 423 K.Three possible transport mechanisms are proposed and examined to explain the generation of reverse surface leakage current.By comparing the experimental data with the numerical transport models,it is found that neither Fowler-Nordheim tunneling nor Frenkel-Poole emission can describe the transport of reverse surface leakage current.However,good agreement is found between the experimental data and the two-dimensional variable range hopping(2D-VRH) model.Therefore,it is concluded that the reverse surface leakage current is dominated by the electron hopping through the surface states at the barrier layer.Moreover,the activation energy of surface leakage current is extracted,which is around 0.083 eV.Finally,the SiN passivated HEMT with a high Al composition and a thin AlGaN barrier layer is also studied.It is observed that 2D-VRH still dominates the reverse surface leakage current and the activation energy is around 0.10 eV,which demonstrates that the alteration of the AlGaN barrier layer does not affect the transport mechanism of reverse surface leakage current in this paper.     

Hot-carrier degradation for 90nm gate length LDD-NMOSFET with ultra-thin gate oxide under low gate voltage stress

The hot-carrier degradation for 90~nm gate length lightly-doped drain (LDD) NMOSFET with ultra-thin (1.4~nm) gate oxide under the low gate voltage (LGV) (at V_g=V_th, where V_th is the threshold voltage) stress has been investigated. It is found that the drain current decreases and the threshold voltage increases after the LGV (V_g=V_th stress. The results are opposite to the degradation phenomena of conventional NMOSFET for the case of this stress. By analysing the gate-induced drain leakage (GIDL) current before and after stresses, it is confirmed that under the LGV stress in ultra-short gate LDD-NMOSFET with ultra-thin gate oxide, the hot holes are trapped at interface in the LDD region and cannot shorten the channel to mask the influence of interface states as those in conventional NMOSFET do, which leads to the different degradation phenomena from those of the conventional NMOS devices. This paper also discusses the degradation in the 90~nm gate length LDD-NMOSFET with 1.4~nm gate oxide under the LGV stress at V_g=V_th with various drain biases. Experimental results show that the degradation slopes (n) range from 0.21 to 0.41. The value of n is less than that of conventional MOSFET (0.5-0.6) and also that of the long gate length LDD MOSFET (\sim0.8).     

Optical and structural investigation of a-plane GaN layers on r-plane sapphire with nucleation layer optimization

Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers:(A) a GaN nucleation layer deposited at low temperature(LT);(B) an AlN nucleation layer deposited at high temperature;or(C) an LT thin AlN nucleation layer with an AlN layer and an AlN/AlGaN superlattice both subsequently deposited at high temperature.The samples have been characterized by Xray diffraction(XRD),atomic force microscopy and photoluminescence.The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A,indicating a reduction in crystal defect density.Furthermore,the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely.The improved optical property,corresponding to the enhanced crystal quality,is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.     

Investigation of passivation effects in AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistor by gate-drain conductance dispersion study

This paper studies the drain current collapse of AlGaN/GaN metal-insulator-semiconductor high electron-mobility transistors (MIS-HEMTs) with NbAlO dielectric by applying dual-pulsed stress to the gate and drain of the device.For NbAlO MIS-HEMT,smaller current collapse is found,especially when the gate static voltage is 8 V.Through a thorough study of the gate-drain conductance dispersion,it is found that the growth of NbAlO can reduce the trap density of the AlGaN surface.Therefore,fewer traps can be filled by gate electrons,and hence the depletion effect in the channel is suppressed effectively.It is proved that the NbAlO gate dielectric can not only decrease gate leakage current but also passivate the AlGaN surface effectively,and weaken the current collapse effect accordingly.     

Influence of double A1N buffer layers on the qualities of GaN films prepared by metal-organic chemical vapour deposition

<正>In this paper we report that the GaN thin film is grown by metal-organic chemical vapour deposition on a sapphire (0001) substrate with double AlN buffer layers.The buffer layer consists of a low-temperature(LT) AlN layer and a high-temperature(HT) AlN layer that are grown at 600℃and 1000℃,respectively.It is observed that the thickness of the LT-AlN layer drastically influences the quality of GaN thin film,and that the optimized 4.25-min-LT-AlN layer minimizes the dislocation density of GaN thin film.The reason for the improved properties is discussed in this paper.     

场板结构AlGaN/GaN HEMT的电流崩塌机理

在不同的漏偏压下,研究了钝化和不同场板尺寸AlGaN/GaN HEMT对电流崩塌的抑制能力.实验结果表明,钝化器件对电流崩塌的抑制能力随着漏偏压的升高而显著下降;在高漏偏压下,场板的尺寸对器件抑制崩塌的能力有较大影响,而合适尺寸的场板结构在各个漏偏压下都能够很好的抑制电流崩塌.深入分析发现,场板结构不仅能够抑制虚栅的充电过程,而且提供了放电途径,有利于虚栅的放电,从而抑制电流崩塌.在此基础上,通过建立场板介质对虚栅放电的模型,解释了高漏偏压下场板的尺寸对器件抑制崩塌的能力有较大影响的原因. 关键词： AlGaN/GaN HEMT 场板 电流崩塌     

复合漏电模型建立及阶梯场板GaN肖特基势垒二极管设计

准垂直GaN肖特基势垒二极管(SBD)因其低成本和高电流传输能力而备受关注.但其主要问题在于无法很好地估计器件的反向特性,从而影响二极管的设计.本文考虑了GaN材料的缺陷以及多种漏电机制,建立了复合漏电模型,对准垂直Ga N SBD的特性进行了模拟,仿真结果与实验结果吻合.基于此所提模型设计出具有高击穿电压的阶梯型场板结构准垂直GaN SBD.根据漏电流、温度和电场在反向电压下的相关性,分析了漏电机制和器件耐压特性,设计的阶梯型场板结构准垂直GaN SBD的Baliga优值BFOM达到73.81 MW/cm~2.