Influence of Schottky drain contacts on the strained AlGaN barrier layer of AlGaN/AlN/GaN heterostructure field-effect transistors

Rectangular Schottky drain AlGaN/AlN/GaN heterostructure field-effect transistors (HFETs) with different gate contact areas and conventional AlGaN/AlN/GaN HFETs as control were both fabricated with same size. It was found there is a significant difference between Schottky drain AlGaN/AlN/GaN HFETs and the control group both in drain series resistance and in two-dimensional electron gas (2DEG) electron mobility in the gate-drain channel. We attribute this to the different influence of Ohmic drain contacts and Schottky drain contacts on the strained AlGaN barrier layer. For conventional AlGaN/AlN/GaN HFETs, annealing drain Ohmic contacts gives rise to a strain variation in the AlGaN barrier layer between the gate contacts and the drain contacts, and results in strong polarization Coulomb field scattering in this region. In Schottky drain AlGaN/AlN/GaN HFETs, the strain in the AlGaN barrier layer is distributed more regularly.     

Study on the drain bias effect on negative bias temperature instability degradation of an ultra-short p-channel metal-oxide-semiconductor field-effect transistor

This paper studies the effect of drain bias on ultra-short p-channel metal-oxide-semiconductor field-effect transistor (PMOSFET) degradation during negative bias temperature (NBT) stress. When a relatively large gate voltage is applied, the degradation magnitude is much more than the drain voltage which is the same as the gate voltage supplied, and the time exponent gets larger than that of the NBT instability (NBTI). With decreasing drain voltage, the degradation magnitude and the time exponent all get smaller. At some values of the drain voltage, the degradation magnitude is even smaller than that of NBTI, and when the drain voltage gets small enough, the exhibition of degradation becomes very similar to the NBTI degradation. When a relatively large drain voltage is applied, with decreasing gate voltage, the degradation magnitude gets smaller. However, the time exponent becomes larger. With the help of electric field simulation, this paper concludes that the degradation magnitude is determined by the vertical electric field of the oxide, the amount of hot holes generated by the strong channel lateral electric field at the gate/drain overlap region, and the time exponent is mainly controlled by localized damage caused by the lateral electric field of the oxide in the gate/drain overlap region where hot carriers are produced.     

Modeling of lightly-doped drain and source contact with boron and nitrogen in graphene nanoribbon

Graphene, a monolayer carbon atoms arranged in hexagonal honeycomb lattice possesses impressive electronic properties. It is utilized as channel, source and drain contact in graphene nanoribbon field-effect transistor (GNRFET). Zigzag graphene nanoribbon (ZGNR) is used as semi-metallic drain and source terminal to a pristine armchair graphene nanoribbon (AGNR) that acts as a semiconducting channel. In addition, a single dopant, either nitrogen or boron is added to create lightly-doped drain and source contact. The electronic properties of graphene nanoribbon (GNR) with lightly-doped drain and source contacts are obtained from tight-binding approach. With self-energy matrices, the lightly-doped contacts Hamiltonian matrices are combined with the pristine channel Hamiltonian matrix. The density of states (DOS) are simulated based on the non-equilibrium Green's Function (NEGF) formalism. Our findings are then compared with published research work. Furthermore, it is demonstrated that the DOS of the overall GNR structure still retain a small band gap and possess semiconducting properties when the channel is connected to semi-metallic contact at the drain and source terminal.     

Reverse blocking enhancement of drain field plate in Schottky-drain AlGaN/GaN high-electron mobility transistors

In this paper, we present the combination of drain field plate(FP) and Schottky drain to improve the reverse blocking capability, and investigate the reverse blocking enhancement of drain FP in Schottky-drain AlGaN/GaN high-electron mobility transistors(HEMTs). Drain FP and gate FP were employed in a two-dimensional simulation to improve the reverse blocking voltage(VRB) and the forward blocking voltage(VFB). The drain-FP length, the gate-FP length and the passivation layer thickness were optimized. VRBand VFBwere improved from-67 V and 134 V to-653 V and 868 V respectively after optimization. Simulation results suggest that the combination of drain FP and Schottky drain can enhance the reverse blocking capability significantly.     

Mechanism of improving forward and reverse blocking voltages in AlGaN/GaN HEMTs by using Schottky drain

In this paper, we demonstrate that a Schottky drain can improve the forward and reverse blocking voltages(BVs)simultaneously in AlGaN/GaN high-electron mobility transistors(HEMTs). The mechanism of improving the two BVs is investigated by analysing the leakage current components and by software simulation. The forward BV increases from72 V to 149 V due to the good Schottky contact morphology. During the reverse bias, the buffer leakage in the Ohmicdrain HEMT increases significantly with the increase of the negative drain bias. For the Schottky-drain HEMT, the buffer leakage is suppressed effectively by the formation of the depletion region at the drain terminal. As a result, the reverse BV is enhanced from-5 V to-49 V by using a Schottky drain. Experiments and the simulation indicate that a Schottky drain is desirable for power electronic applications.     

Effects of Unintended Dopants on I-V Characteristics of the Double-Gate MOSFETs,a Simulation Study

In this paper, we study the effects of an unintended dopant in the channel on the current-voltage characteristics of a Double-Gate (DG) Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). Non-Equilibrium Green's Function (NEGF) approach is used. A quantum transport model to calculate the drain current is presented and subthreshold swing and drain induced barrier lowering (DIBL) effect are studied.     

Influence of a drain field plate on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor

In this paper,the influence of a drain field plate(FP)on the forward blocking characteristics of an AlGaN/GaN high electron mobility transistor(HEMT)is investigated.The HEMT with only a gate FP is optimized,and breakdown voltage VBRis saturated at 1085 V for gate–drain spacing LGD≥8μm.On the basis of the HEMT with a gate FP,a drain FP is added with LGD=10μm.For the length of the drain FP LDF≤2μm,VBRis almost kept at 1085 V,showing no degradation.When LDFexceeds 2μm,VBRdecreases obviously as LDFincreases.Moreover,the larger the LDF,the larger the decrease of VBR.It is concluded that the distance between the gate edge and the drain FP edge should be larger than a certain value to prevent the drain FP from affecting the forward blocking voltage and the value should be equal to the LGDat which VBR begins to saturate in the first structure.The electric field and potential distribution are simulated and analyzed to account for the decrease of VBR.     

AlGaN表面坑状缺陷及GaN缓冲层位错缺陷对AlGaN/GaN HEMT电流崩塌效应的影响

利用金属有机气相外延(MOVPE)技术生长了具有不同AlGaN表面坑状缺陷和GaN缓冲层位错缺陷密度的AlGaN/GaN 高电子迁移率晶体管(HEMT)样品,并对比研究了两种缺陷对器件栅、漏延迟电流崩塌效应的影响.栅延迟测试表明,AlGaN表面坑状缺陷会引起栅延迟电流崩塌效应和源漏电阻的增加,而且表面坑状缺陷越多,栅延迟电流崩塌程度和源漏电阻的增加越明显.漏延迟测试显示,AlGaN表面坑状缺陷对漏延迟电流崩塌影响不大,而GaN缓冲层位错缺陷主要影响漏延迟电流崩塌.研究结果表明,AlGaN表面坑状缺陷和Ga 关键词： AlGaN/GaN HEMT 电流崩塌 坑状缺陷 位错缺陷     

高$lt;i$gt;k$lt;/i$gt;栅介质小尺寸全耗尽绝缘体上锗p型金属氧化物半导体场效应晶体管漏源电流模型

通过求解沟道的二维泊松方程得到沟道表面势和沟道反型层电荷, 建立了高k栅介质小尺寸绝缘体上锗(GeOI) p型金属氧化物半导体场效应晶体管(PMOSFET)的漏源电流解析模型. 模型包括了速度饱和效应、迁移率调制效应和沟长调制效应, 同时考虑了栅氧化层和埋氧层与沟道界面处的界面陷阱电荷、氧化层固定电荷对漏源电流的影响. 在饱和区和非饱和区, 漏源电流模拟结果与实验数据符合得较好, 证实了模型的正确性和实用性. 利用建立的漏源电流模型模拟分析了器件主要结构和物理参数对跨导、漏导、截止频率和电压增益的影响, 对GeOI PMOSFET的设计具有一定的指导作用. 关键词： 绝缘体上锗p型金属氧化物半导体场效应晶体管 漏源电流模型 跨导 截止频率     

Mechanism of NBTI Recovery under Negative Voltage Stress

Recovery phenomenon is observed under negative gate voltage stress which is smaller than the previous degradation stress. We focus on the drain current to study the degradation and recovery of negative bias temperature instability (NBTI) with a real-time method. By this method, different recovery phenomena among different size devices are observed. Under negative recovery stress, the drain current gradually recovers for the large size devices and gets into recovery saturation when long recovery time is involved. For small-size devices, a step-like recovery of drain current is observed. The recovery of the drain current is mainly caused by the holes detrapping and tunnelling back to the channel surface which are trapped in oxide. The model of hole detrapping explains the recovery under negative voltage stress reasonably.     

GaSb p-channel metal-oxide-semiconductor field-effect transistor and its temperature dependent characteristics

GaSb p-channel metal-oxide-semiconductor field-effect transistors(MOSFETs)with an atomic layer deposited Al2O3gate dielectric and a self-aligned Si-implanted source/drain are experimentally demonstrated.Temperature dependent electrical characteristics are investigated.Different electrical behaviors are observed in two temperature regions,and the underlying mechanisms are discussed.It is found that the reverse-bias pn junction leakage of the drain/substrate is the main component of the off-state drain leakage current,which is generation-current dominated in the low temperature regions and is diffusion-current dominated in the high temperature regions.Methods to further reduce the off-state drain leakage current are given.     

The role of metal contacts in the stability of n-type organic field effect transistors

We are presenting a long-time bias stress stability of C₆₀-based n-type organic field effect transistors (OFETs), in bottom gate, top contacts configuration, with aluminium (Al), silver (Ag) and gold (Au) source–drain contacts. The results clearly shows that the bias stress effects in C₆₀-based n-type OFETs is similar to p-type OFETs and it can be reduced by using an appropriate metal for the source–drain contacts. During the bias stress time, the threshold voltage shift and an increase in the contacts resistance have also been measured. On the basis of the stability of the device parameters, it is proposed that the Al source–drain contact-based devices gives better stability as compared to the devices with Ag and Au source–drain contacts. Our results show that the bias stress-induced threshold voltage shift is due to the trapping of charges in the channel region and in the vicinity of the source–drain contacts.     

浮顶罐中央排水管泄漏油气扩散激光检测研究

浮顶罐中央排水管油气泄漏研究对及时制定合理的应急措施、预防重大事故发生有重要意义。介绍了一种判断中央排水管泄漏的方法。通过数值模拟分析了不同泄漏位置对中央排水管泄漏后报警时间的影响,模拟发现3个泄漏位置的报警时间最大相差1 308 s,说明泄漏位置对报警时间的影响较大。采用浓度为10%的甲烷代替油气进行了中央排水管油气泄漏激光检测可行性的实验验证。结果表明:TDLAS技术可用于中央排水管泄漏报警系统中油气浓度的检测, 对浮顶罐中央排水管泄漏报警系统的设计有一定的参考意义。     

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.     

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     

Analytical modeling and simulation of subthreshold behavior in nanoscale dual material gate AlGaN/GaN HEMT

A two-dimensional (2-D) analytical model for a Dual Material Gate (DMG) AlGaN/GaN High Electron Mobility Transistor (HEMT) has been developed to demonstrate the unique attributes of this device structure in suppressing short channel effects (SCEs). The model accurately predicts the channel potential, electric field variation along the channel, and sub-threshold drain current, taking into account the effect of lengths of the two gate metals, their work functions, barrier layer thicknesses, and applied drain biases. It is seen that the SCEs and hot carrier effects in DMG AlGaN/GaN HEMT are suppressed due to the work function difference of the two metal gates, thereby screening the drain potential variations by the gate near the drain. Besides, a more uniform electric field along the channel leads to improved carrier transport efficiency. The accuracy of the results obtained from our analytical model has been verified using ATLAS device simulations.     

Exploring the warped bulk

In this study, a gallium nitride (GaN) high electron mobility transistor (HEMT) with recessed insulator and barrier is reported. In the proposed structure, insulator is recessed into the barrier at the drain side and barrier is recessed into the buffer layer at the source side. We study important device characteristics such as electric field, breakdown voltage, drain current, maximum output power density, gate-drain capacitance, short channel effects and DC transconductance using two-dimensional and two-carrier device simulator. Recessed insulator in the drain side of the proposed structure reduces maximum electric field in the channel and therefore increases the breakdown voltage and maximum output power density compared to the conventional counterpart. Also, gate-drain capacitance value in the proposed structure is less than that of the conventional structure. Overall, the proposed structure reduces short channel effects. Because of the recessed regions at both the source and the drain sides, the average barrier thickness of the proposed structure is not changed. Thus, the drain current of the proposed structure is almost equivalent to that of the conventional transistor. In this work, length (L _r) and thickness (T _r) of the recessed region of the barrier at the source side are the same as those of the insulator at the drain side.     

Novel attributes of AlGaN/AlN/GaN/SiC HEMTs with the multiple indented channel

In this paper, a high performance AlGaN/AlN/GaN/SiC High Electron Mobility Transistor (HEMT) with the multiple indented channel (MIC-HEMT) is proposed. The main focus of the proposed structure is based on reduction of the space around the gate, stop of the spread of the depletion region around the source–drain, and decrement of the thickness of the channel between the gate and drain. Therefore, the breakdown voltage increases, meanwhile the elimination of the gate depletion layer extension to source/drain decreases the gate–source and gate–drain capacitances. The optimized results reveal that the breakdown voltage and the drain saturation current increase about 178% and 46% compared with a conventional HEMT (C-HEMT), respectively. Therefore, the maximum output power density is improved by factor 4.1 in comparison with conventional one. Also, the cut-off frequency of 25.2 GHz and the maximum oscillation frequency of 92.1 GHz for the MIC-HEMT are obtained compared to 13 GHz and 43 GHz for that of the C-HEMT and the minimum figure noise decreased consequently of reducing the gate–drain and gate–source capacitances by about 42% and 40%, respectively. The proposed MIC-HEMT shows a maximum stable gain (MSG) exceeding 24.1 dB at 3.1 GHz which the greatest gain is yet reported for HEMTs, showing the potential of this device for high power RF applications.     

具有纵向漏极场板的低导通电阻绝缘体上硅横向双扩散金属氧化物半导体器件新结构

为降低绝缘体上硅(SOI)横向双扩散金属氧化物半导体(LDMOS)器件的导通电阻,同时提高器件击穿电压,提出了一种具有纵向漏极场板的低导通电阻槽栅槽漏SOI-LDMOS器件新结构.该结构特征为采用了槽栅槽漏结构,在纵向上扩展了电流传导区域,在横向上缩短了电流传导路径,降低了器件导通电阻;漏端采用了纵向漏极场板,该场板对漏端下方的电场进行了调制,从而减弱了漏极末端的高电场,提高了器件的击穿电压.利用二维数值仿真软件MEDICI对新结构与具有相同器件尺寸的传统SOI结构、槽栅SOI结构、槽栅槽漏SOI结构进行了比较.结果表明:在保证各自最高优值的条件下,与这三种结构相比,新结构的比导通电阻分别降低了53%,23%和提高了87%,击穿电压则分别提高了4%、降低了9%、提高了45%.比较四种结构的优值,具有纵向漏极场板的槽栅槽漏SOI结构优值最高,这表明在四种结构中新结构保持了较低导通电阻,同时又具有较高的击穿电压.     

Photoelectric spectroscopy of oxide states with MOS structures atT=79 K

AtT=79 K illumination effects with visible and UV light on the drain current were studied forn-channel enhancement-type MOS transistors. The results show that the response of photoelectric measurements is due to electron excitation from oxide states into the silicon surface layer (positive changes of drain current). The oxide states lying near the bottom of the silicon dioxide conduction band are distributed in energy. Oxide states having captured a hole can be discharged by electrons excited from the silicon conduction or valence band (negative changes of drain current) in combination with a tunneling process.