High temperature characteristics of AlGaN/GaN high electron mobility transistors

Direct current (DC) and pulsed measurements are performed to determine the degradation mechanisms of AlGaN/GaN high electron mobility transistors (HEMTs) under high temperature. The degradation of the DC characteristics is mainly attributed to the reduction in the density and the mobility of the two-dimensional electron gas (2DEG). The pulsed measurements indicate that the trap assisted tunneling is the dominant gate leakage mechanism in the temperature range of interest. The traps in the barrier layer become active as the temperature increases, which is conducive to the electron tunneling between the gate and the channel. The enhancement of the tunneling results in the weakening of the current collapse effects, as the electrons trapped by the barrier traps can escape more easily at the higher temperature.     

具有部分本征GaN帽层新型AlGaN/GaN高电子迁移率晶体管特性分析

为了优化传统Al GaN/GaN高电子迁移率晶体管(high electron mobility transistors,HEMTs)器件的表面电场,提高击穿电压,本文提出了一种具有部分本征GaN帽层的新型Al GaN/GaN HEMTs器件结构.新型结构通过在Al GaN势垒层顶部、栅电极到漏电极的漂移区之间引入部分本征GaN帽层,由于本征GaN帽层和Al GaN势垒层界面处的极化效应,降低了沟道二维电子气(two dimensional electron gas,2DEG)的浓度,形成了栅边缘低浓度2DEG区域,使得沟道2DEG浓度分区,由均匀分布变为阶梯分布.通过调制沟道2DEG的浓度分布,从而调制了Al GaN/GaN HEMTs器件的表面电场.利用电场调制效应,产生了新的电场峰,且有效降低了栅边缘的高峰电场,Al GaN/GaN HEMTs器件的表面电场分布更加均匀.利用ISE-TCAD软件仿真分析得出:通过设计一定厚度和长度的本征GaN帽层,Al GaN/GaN HEMTs器件的击穿电压从传统结构的427 V提高到新型结构的960 V.由于沟道2DEG浓度减小,沟道电阻增加,使得新型Al GaN/GaN HEMTs器件的最大输出电流减小了9.2%,截止频率几乎保持不变,而最大振荡频率提高了12%.     

Effect of overdrive voltage on PBTI trapping behavior in GaN MIS-HEMT with LPCVD SiNx gate dielectric

The effect of high overdrive voltage on the positive bias temperature instability(PBTI)trapping behavior is investigated for GaN metal–insulator–semiconductor high electron mobility transistor(MIS-HEMT)with LPCVD-SiNx gate dielectric.A higher overdrive voltage is more effective to accelerate the electrons trapping process,resulting in a unique trapping behavior,i.e.,a larger threshold voltage shift with a weaker time dependence and a weaker temperature dependence.Combining the degradation of electrical parameters with the frequency–conductance measurements,the unique trapping behavior is ascribed to the defect energy profile inside the gate dielectric changing with stress time,new interface/border traps with a broad distribution above the channel Fermi level are introduced by high overdrive voltage.     

Low power fluorine plasma effects on electrical reliability of AlGaN/GaN high electron mobility transistor

The new electrical degradation phenomenon of the AlGaN/GaN high electron mobility transistor(HEMT) treated by low power fluorine plasma is discovered. The saturated current, on-resistance, threshold voltage, gate leakage and breakdown voltage show that each experiences a significant change in a short time stress, and then keeps unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. These results suggest that the low power fluorine implant ion stays in an unstable state. It causes the electrical properties of AlGaN/GaN HEMT to present early degradation. A new migration and degradation mechanism of the low power fluorine implant ion under the off-stress electrical stress is proposed. The low power fluorine ions would drift at the beginning of the off-state stress, and then accumulate between gate and drain nearby the gate side. Due to the strong electronegativity of fluorine, the accumulation of the front fluorine ions would prevent the subsequent fluorine ions from drifting, thereby alleviating further the degradation of AlGaN/GaN HEMT electrical properties.     

Electrical characteristics of AlInN/GaN HEMTs under cryogenic operation

Electrical properties of an AlInN/GaN high-electron mobility transistor (HEMT) on a sapphire substrate are investi-gated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AlInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.     

具有高开启/关断电流比的Al2O3/AlGaN/GaN金属氧化物半导体高电子迁移率晶体管

采用原子层淀积(ALD)方法,制备了Al₂O₃为栅介质的高性能AlGaN/GaN金属氧化物半导体高电子迁移率晶体管(MOS-HEMT)。在栅压为-20 V时,MOS-HEMT的栅漏电比Schottky-gate HEMT的栅漏电低4个数量级以上。在栅压为+2 V时,Schottky-gate HEMT的栅漏电为191μA;在栅压为+20 V时,MOS-HEMT的栅漏电仅为23.6 nA,比同样尺寸的Schottky-gate HEMT的栅漏电低将近7个数量级。AlGaN/GaN MOS-HEMT的栅压摆幅达到了±20 V。在栅压V_gs=0 V时, MOS-HEMT的饱和电流密度达到了646 mA/mm,相比Schottky-gate HEMT的饱和电流密度(277 mA/mm)提高了133%。栅漏间距为10μm的AlGaN/GaN MOS-HEMT器件在栅压为+3 V时的最大饱和输出电流达到680 mA/mm,特征导通电阻为1.47 mΩ·cm²。Schottky-gate HEMT的开启与关断电流比仅为10⁵,MOS-HEMT的开启与关断电流比超过了10⁹,超出了Schottky-gate HEMT器件4个数量级,原因是栅漏电的降低提高了MOS-HEMT的开启与关断电流比。在V_gs=-14 V时,栅漏间距为10μm的AlGaN/GaN MOS-HEMT的关断击穿电压为640 V,关断泄露电流为27μA/mm。     

Investigation of trap states in Al_2O_3 InAlN/GaN metal–oxide–semiconductor high-electron-mobility transistors

In this paper the trapping effects in Al2O3/In0.17Al0.83N/Ga N MOS-HEMT(here, HEMT stands for high electron mobility transistor) are investigated by frequency-dependent capacitance and conductance analysis. The trap states are found at both the Al2O3/In Al N and In Al N/Ga N interface. Trap states in In Al N/Ga N heterostructure are determined to have mixed de-trapping mechanisms, emission, and tunneling. Part of the electrons captured in the trap states are likely to tunnel into the two-dimensional electron gas(2DEG) channel under serious band bending and stronger electric field peak caused by high Al content in the In Al N barrier, which explains the opposite voltage dependence of time constant and relation between the time constant and energy of the trap states.     

Degraded model of radiation-induced acceptor defects for GaN-based high electron mobility transistors （HEMTs）

Using depletion approximation theory and introducing acceptor defects which can characterize radiation induced deep-level defects in AlGaN/GaN heterostructures, we set up a radiation damage model of AlGaN/GaN high electron mobility transistor (HEMT) to separately simulate the effects of several main radiation damage mechanisms and the complete radiation damage effect simultaneously considering the degradation in mobility. Our calculated results, consistent with the experimental results, indicate that thin AlGaN barrier layer, high Al content and high doping concentration are favourable for restraining the shifts of threshold voltage in the AlGaN/GaN HEMT; when the acceptor concentration induced is less than 10¹⁴cm^-3, the shifts in threshold voltage are not obvious; only when the acceptor concentration induced is higher than 10¹⁶cm^-3, will the shifts of threshold voltage remarkably increase; the increase of threshold voltage, resulting from radiation induced acceptor, mainly contributes to the degradation in drain saturation current of the current--voltage (I--V) characteristic, but has no effect on the transconductance in the saturation area.     

阶梯AlGaN外延新型Al0.25Ga0.75N/GaNHEMTs器件实验研究

本文报道了作者提出的阶梯AlGaN外延层新型AlGaN/GaN HEMTs结构的实验结果. 实验利用感应耦合等离子体刻蚀(ICP)刻蚀栅边缘的AlGaN外延层, 形成阶梯的AlGaN 外延层结构, 获得浓度分区的沟道2DEG, 使得阶梯AlGaN外延层边缘出现新的电场峰, 有效降低栅边缘的高峰电场, 从而优化了AlGaN/GaN HEMTs器件的表面电场分布. 实验获得了阈值电压-1.5 V的新型AlGaN/GaN HEMTs器件. 经过测试, 同样面积的器件击穿电压从传统结构的67 V提高到新结构的106 V, 提高了58%左右; 脉冲测试下电流崩塌量也比传统结构减少了30%左右, 电流崩塌效应得到了一定的缓解.     

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.     

High-field-induced electron detrapping in An AlGaN/GaN high electron mobility transistor

A step stress test is carried out to study the reliability characteristics of an AlGaN/GaN high electron mobility transistor(HEMT).An anomalous critical drain-to-gate voltage with a negative temperature coefficient is observed in the stress sequence,beyond which the HEMT device starts to recover from degradation induced by early lower voltage stress.While the performance degradation featuring the drain current slump stems from electron trapping in the surface or bulk states during low-to-medium bias stress,the recovery is attributed to high field induced electron detrapping.The carrier detrapping mechanism could be helpful for lessening the trapping-related performance degradation of a GaN-based HEMT.     

Negative transconductance effect in p-GaN gate AlGaN/GaN HEMTs by traps in unintentionally doped GaN buffer layer

We investigate the negative transconductance effect in p-GaN gate AlGaN/GaN high-electron-mobility transistor(HEMT) associated with traps in the unintentionally doped GaN buffer layer. We find that a negative transconductance effect occurs with increasing the trap concentration and capture cross section when calculating transfer characteristics.The electron tunneling through AlGaN barrier and the reduced electric field discrepancy between drain side and gate side induced by traps are reasonably explained by analyzing the band diagrams, output characteristics, and the electric field strength of the channel of the devices under different trap concentrations and capture cross sections.     

An AlGaN/GaN HEMT with a reduced surface electric field and an improved breakdown voltage

A reduced surface electric field in an AlGaN/GaN high electron mobility transistor(HEMT) is investigated by employing a localized Mg-doped layer under the two-dimensional electron gas(2-DEG) channel as an electric field shaping layer.The electric field strength around the gate edge is effectively relieved and the surface electric field is distributed evenly as compared with those of HEMTs with conventional source-connected field plate and double field plate structures with the same device physical dimensions.Compared with the HEMTs with conventional sourceconnected field plates and double field plates,the HEMT with a Mg-doped layer also shows that the breakdown location shifts from the surface of the gate edge to the bulk Mg-doped layer edge.By optimizing both the length of Mg-doped layer,L m,and the doping concentration,a 5.5 times and 3 times the reduction in the peak electric field near the drain side gate edge is observed as compared with those of the HEMTs with source-connected field plate structure and double field plate structure,respectively.In a device with V GS = -5 V,L m = 1.5 μm,a peak Mg doping concentration of 8×10 17cm-3 and a drift region length of 10 μm,the breakdown voltage is observed to increase from 560 V in a conventional device without field plate structure to over 900 V without any area overhead penalty.     

A bistable, self-latching inverter by the monolithic integration of resonant tunnelling diode and high electron mobility transistor

This paper reports that the structures of AlGaAs/InGaAs high electron mobility transistor (HEMT) and AlAs/GaAs resonant tunnelling diode (RTD) are epitaxially grown by molecular beam epitaxy (MBE) in turn on a GaAs substrate. An Al_0.24Ga_0.76As chair barrier layer, which is grown adjacent to the top AlAs barrier, helps to reduce the valley current of RTD. The peak-to-valley current ratio of fabricated RTD is 4.8 and the transconductance for the 1-μm gate HEMT is 125mS/mm. A static inverter which consists of two RTDs and a HEMT is designed and fabricated. Unlike a conventional CMOS inverter, the novel inverter exhibits self-latching property.     

不同量子阱宽度的InP基In0.53GaAs/In0.52AlAs高电子迁移率晶体管材料二维电子气的性能研究

用Shubnikov-de Haas(SdH)振荡效应，研究了在1.4 K下不同量子阱宽度(10—35 nm)的InP基高电子迁移率晶体管材料的二维电子气特性.通过对纵向电阻SdH振荡的快速傅里叶变换分析，得到不同阱宽时量子阱中二维电子气各子带电子浓度和量子迁移率.研究发现，在Si掺杂浓度一定时，阱宽的改变对于量子阱中总的载流子浓度改变不大，但是随着阱宽的增加，阱中的电子从占据一个子带到占据两个子带，且第二子带上的载流子迁移率远大于第一子带迁移率.当量子阱宽度为20 nm时，处在第二子能级上的电子数与处在 关键词： 量子阱宽 二维电子气 Shubnikov-de Haas振荡 高电子迁移率晶体管     

高电子迁移率晶体管放大器高功率微波损伤机理

在TCAD半导体仿真环境中,建立了0.25 m栅长的AlGaAs/InGaAs高电子迁移率晶体管(HEMT)低噪声放大器与微波脉冲作用的仿真模型,基于器件内部的电场强度、电流密度和温度分布的变化,研究了1 GHz的微波从栅极和漏极注入的损伤机理。研究结果表明,从栅极注入约40.1 dBm的微波时,HEMT内部峰值温度随着时间的变化振荡上升,最终使得器件失效,栅下靠源侧电流通道和强电场的同时存在使得该位置最容易损伤;从漏极注入微波时,注入功率的高低会使器件内部出现不同的响应过程,注入功率存在一个临界值,高于该值,器件有可能在第一个周期内损伤,损伤位置均在漏极附近。在1 GHz的微波作用下,漏极注入比栅极注入更难损伤。     

The degradation mechanism of an AlGaN/GaN high electron mobility transistor under step-stress

Step-stress experiments are performed in this paper to investigate the degradation mechanism of an AlGaN/GaN high electron mobility transistor(HEMT).It is found that the stress current shows a recoverable decrease during each voltage step and there is a critical voltage beyond which the stress current starts to increase sharply in our experiments.We postulate that defects may be randomly induced within the AlGaN barrier by the high electric field during each voltage step.But once the critical voltage is reached,the trap concentration will increase sharply due to the inverse piezoelectric effect.A leakage path may be introduced by excessive defect,and this may result in the permanent degradation of the AlGaN/GaN HEMT.     

Snapback应力引起的90 nm NMOSFET's栅氧化层损伤研究

实验结果发现突发击穿(snapback)，偏置下雪崩热空穴注入NMOSFET栅氧化层，产生界面态，同时空穴会陷落在氧化层中.由于栅氧化层很薄，陷落的空穴会与隧穿入氧化层中的电子复合形成大量中性电子陷阱，使得栅隧穿电流不断增大.这些氧化层电子陷阱俘获电子后带负电，引起阈值电压增大、亚阈值电流减小.关态漏泄漏电流的退化分两个阶段：第一阶段亚阈值电流是主要成分，第二阶段栅电流是主要成分.在预加热电子(HE)应力后，HE产生的界面陷阱在snapback应力期间可以屏蔽雪崩热空穴注入栅氧化层，使器件snapback开态和关态特性退化变小. 关键词： 突发击穿 软击穿 应力引起的泄漏电流 热电子应力     

Structural characterization of Mg substituted on A/B sites in $$\hbox {NiFe}_2\hbox {O}_4$$ nanoparticles using autocombustion method

A compact quantitative model based on oxide semiconductor interface density of states (DOS) is proposed for Al_0.25Ga_0.75N/GaN metal oxide semiconductor high electron mobility transistor (MOSHEMT). Mathematical expressions for surface potential, sheet charge concentration, gate capacitance and threshold voltage have been derived. The gate capacitance behaviour is studied in terms of capacitance–voltage (CV) characteristics. Similarly, the predicted threshold voltage (V _T) is analysed by varying barrier thickness and oxide thickness. The positive V _T obtained for a very thin 3 nm AlGaN barrier layer enables the enhancement mode operation of the MOSHEMT. These devices, along with depletion mode devices, are basic constituents of cascode configuration in power electronic circuits. The expressions developed are used in conventional long-channel HEMT drain current equation and evaluated to obtain different DC characteristics. The obtained results are compared with experimental data taken from literature which show good agreement and hence endorse the proposed model.     

量子点浮置栅量子线沟道三栅结构单电子场效应管存储特性的数值模拟

通过建立二维薛定谔方程和泊松方程数值模型,对基于硅量子点浮置栅和硅量子线沟道三栅结构单电子场效应管(FET)存储特性进行了研究.通过在不同尺寸、栅压和不同写入电荷条件下,对硅量子线沟道中电子浓度的二维有限元自洽数值求解,研究了在纳米尺度下硅量子线沟道中量子限制效应和电荷分布对于器件特性的影响.模拟结果发现,沟道的导通阈值电压随着尺寸的缩小而提高,并随浮置栅内存储的电子数目的增加而明显升高.然而,这样的增加趋势在受到纳米尺度沟道中高电荷密度的影响下将出现非线性饱和趋势.进一步研究发现,当沟道尺寸较小时,沟道 关键词： 三栅单电子FET存储器 量子效应 薛定谔方程 泊松方程