6H-SiC Schottky二极管的正向特性

提出了一种考虑Schottky结势垒不均匀性和界面层作用的SiC Schottky二极管(SBD)正向特性模型,势垒的不均匀性来自于SiC外延层上的各种缺陷,而界面层上的压降会使正向Schottky结的有效势垒增高.该模型能够对不同温度下SiC Schottky结正向特性很好地进行模拟,模拟结果和测量数据相符.它更适用于考虑器件温度变化的场合,从机理上说明了理想因子、有效势垒和温度的关系.     

ZnO/Si异质结中的晶界层行为研究

本文利用电容-电压,电流-电压和深能级瞬态谱研究了ZnO/Si异质结的晶界层行为和载流子的输运机制。当存在高密度界面态时,ZnO/Si异质结的载流子输运受到晶界层的控制。我们观察到了有趣的现象,不同测量温度下得到的ZnO/Si异质结正向lnI-V曲线发生交叉,另外得到ZnO/Si异质结的有效势垒高度随着测量温度的下降而下降,这与理想的异质结热发射模型是相矛盾的。本文的随后各节对上面提到的现象做出解释。     

固体C_(60)/n型GaAs接触电学性质

本文研究了固体C60和n型GaAs构成的异质结的电学特性，电流-电压测量结果表明这种接触具有相当理想的整流特性，其理想因子接近于1．电流-温度测量表明，在固定正向偏压下，其电流是温度的指数函数，从中可以确定接触的有效势垒高度为1．02eV高频C-V和深能级瞬态谱（DLTS）测量结果表明，在GaAs导带以下0．35eV附近存在着密度为1011／cm2的界面态，这些界面态可能起源于C60和GaAs的相互作用．     

固相反应制备的多晶和外延CoSi_2/n-Si(111)接触的肖特基特性

通过硅 (111)衬底淀积的单层 Co或 Co/ Ti双金属层在不同退火温度的固相反应 ,在硅上形成制备了多晶和外延 Co Si2 薄膜 .用电流 -电压和电容 -电压 (I- V/ C- V)技术在 90 K到室温的温度范围内测量了 Co Si2 / Si肖特基接触特性。用肖特基势垒不均匀模型分析了所测得的 I- V特性 ,在较高温度下 (≥～ 2 0 0 K)或较低温度的较大偏压区域 ,I- V曲线能用热激发和在整个结面积上势垒高度的高斯分布模型描述 .而在较低温度的较小偏压区域 ,电流由流过一些小势垒高度微区的电流决定 ,从而在低温 I- V曲线上在约 10 - 7A处有一个“曲折”.     

PECVD多晶金刚石平面薄膜场发射特性

以n-Si为衬底，用PECVD方法淀积了多晶金刚石薄膜。采用以金刚石薄膜为阴极的二极管结构测试了场发射特性，在6V/μm的电场下，场发射电流为5μA。研究了场发射的有效势垒随外加电场的变化，发现在有效势垒随外电场变化的曲线中存在一段平台。从理论上对这种现象进行了研究，分析了电子从Si衬底注入金刚石薄膜的方式，认为有效势垒的平台是由于缺陷能级在金刚石禁带中分布不均匀所致，并由此建立了在注入限制情况下多晶金刚石薄膜的场发射模型。根据模型计算得到有效势垒的理论曲线与实验曲线，反映了相同的变化规律。     

SiGe/SiHBT异质界面与pn结界面的相对位移的影响

从模拟和实验两方面研究了SiGe/Si HBT发射结中pn结界面和SiGe/Si界面的相对位置对器件的电流增益和频率特性的影响.发现两界面偏离时器件性能会变差.尤其是当pn结位于SiGe/Si界面之前仅几十?就足以产生相当高的电子寄生势垒,严重恶化器件的性能.据此分析了基区B杂质的偏析和外扩对器件的影响以及SiGe/Si隔离层的作用.     

带有复合掺杂层集电区的InP/InGaAs/InP DHBT直流特性分析

设计了一种新结构InP/InGaAs/InP双异质结双极晶体管(DHBT),在集电区与基区之间插入n+-InP层,以降低集电结的导带势垒尖峰,克服电流阻挡效应.采用基于热场发射和连续性方程的发射透射模型,计算了n+-InP插入层掺杂浓度和厚度对InP/InGaAs/InP DHBT集电结导带有效势垒高度和I-V特性的影响.结果表明,当n+-InP插入层掺杂浓度为3×1019cm-3、厚度为3nm时,可以获得较好的器件特性.采用气态源分子束外延(GSMBE)技术成功地生长出InP/InGaAs/InP DHBT结构材料.器件研制结果表明,所设计的DHBT材料结构能有效降低集电结的导带势垒尖峰,显著改善器件的输出特性.     

带有复合掺杂层集电区的InP/InGaAs/InP DHBT直流特性分析

设计了一种新结构InP/InGaAs/InP双异质结双极晶体管(DHBT),在集电区与基区之间插入n -InP层,以降低集电结的导带势垒尖峰,克服电流阻挡效应.采用基于热场发射和连续性方程的发射透射模型,计算了n -InP插入层掺杂浓度和厚度对InP/InGaAs/InP DHBT集电结导带有效势垒高度和I-V特性的影响.结果表明,当n -InP插入层掺杂浓度为3×1019cm-3、厚度为3nm时,可以获得较好的器件特性.采用气态源分子束外延(GSMBE)技术成功地生长出InP/InGaAs/InP DHBT结构材料.器件研制结果表明,所设计的DHBT材料结构能有效降低集电结的导带势垒尖峰,显著改善器件的输出特性.     

(AlGa)As/GaAs DH激光器低温负阻的研究

在室温至 77K范围内测量了 AlGaAs/GaAs DH激光器的正向伏安特性.发现有些激光器在低温下具有负阻的特性. 采用类 Schottky模型对DH激光器中的N-Al_(0.3)Ga_(0.7)As/n-GaAs异质结的电流传输特性进行分析,认为负阻现象是由于N型(AlGa)As层掺杂浓度偏低,N-n异质结在低温DH激光器正向偏置较大时,电子从n区隧道击穿N-n异质结势垒,或空穴从P型有源区注入N区引起的.此外N-AlGaAs层的施主杂质Sn的电离能很大也对低温负阻有贡献.     

AlGaInP大功率半导体激光器的漏电分析

对于GaInP/AlGaInP量子阱激光器,在大电流注入或高温工作时有源区中注入的电子会越过势垒进入p型限制层成为漏电流,严重影响器件的正常工作.本文通过测试AlGaInP大功率压应变量子阱激光器的阈值电流和外微分量子效率随温度的变化,拟合出有源区电子的有效势垒高度,并与理论模拟结果进行了比较,讨论了p型限制层掺杂浓度的分布对势垒高度的影响.     

Ohmic contact behaviour of Co/C/4H-SiC structures

The electrical contact properties of Co/4H-SiC structures are investigated.A carbon interfacial layer between a Co film and SiC is used to improve the Ohmic contact properties significantly.The C film is deposited prior to Co film deposition on SiC using DC sputtering.The high quality Ohmic contact and specific contact resistivity of 2.30×10^-6Ω·cm² are obtained for Co/C/SiC structures after two-step annealing at 500℃for 10 min and 1050℃for 3 min.The physical properties of the contacts are examined by using XRD.The results indicate that the Co-based metal contacts have better structural stability of silicide phases formed after the high temperature annealing and carbon-enriched layer is produced below the contact,playing a key role in forming an Ohmic contact through the reduction of effective Schottky barrier height for the transport of electrons.The thermal stability of Au/Co/C/SiC Ohmic contacts is investigated.The contacts remain Ohmic on doped n-type(2.8×10¹⁸ cm^-3) 4H-SiC after thermal aging treatment at 500℃for 20 h.     

Role of Interface Layers and Localized States in TiAl-Based Ohmic Contacts to <Emphasis Type="Italic">p-</Emphasis>Type 4H-SiC

We have investigated the roles of interfacial reaction, work function variation, and localized states of annealed Ti/Al ohmic contacts to p-type 4H-SiC. The Al was found to be absent in the near interface region. The possibility of additional p-doping by Al indiffusion in the top SiC layer was ruled out. The work function of Ti₃SiC₂, the direct contact layer to SiC, was determined to be intermediate between Ti and p-SiC, leading to a considerably lowered Schottky barrier height. Reaction-induced interfacial states were observed in the near-interface SiC, which may further reduce the barrier height and cause the formation of ohmic contact.     

Electrical characteristics of GaAs MIS Schottky diodes

The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of GaAs metal-insulator-semiconductor (MIS) Schottky barrier diodes are investigated over a wide temperature range and compared with MS diodes. The effects of the insulating layer on barrier height and carrier transport are delineated by an activation energy analysis. Excess currents observed at low forward and reverse bias have also been analyzed and their cause identified. A capacitance anomaly consistently noticed in MIS Schottky barriers is resolved by stipulating a non-uniform interfacial layer, and a self-consistent model of the GaAs MIS Schottky barrier is developed by analyzing I-V and C-V data of both MIS and MS diodes.     

Measurement of Richardson constant of GaAs Schottky barriers

The Richardson constants for near-ideal AuGaAs and AlGaAs Schottky diodes have been determined from an analysis of forward current-voltage characteristics. Measurement of capacitance-voltage characteristics at different temperatures shows that the barrier heights of the diodes have very similar temperature dependence for both Au and Al contacts. On taking into account the temperature dependence of the barrier height, the corrected value of the Richardson constant for AuGaAs diode is found to be very close to the predicted theoretical value. The corresponding value for AlGaAs diode is about a factor of five smaller which is explained on the basis of a thin interfacial layer between Al and GaAs.     

用弹道电子发射显微术研究超薄金属硅化物/硅肖特基接触

采用弹道电子发射显微术 ( BEEM)技术对超薄 Pt Si/Si、Co Si2 /Si肖特基接触特性进行了研究 ,并与电流 -电压 ( I- V)及电容 -电压 ( C- V)测试结果进行了对比 .研究了 Ar离子轰击对超薄Pt Si/n- Si肖特基接触特性的影响 .BEEM、I- V/C- V技术对多种样品的研究结果表明 ,I- V/C- V测试会由于超薄硅化物层串联电阻的影响而使测试结果产生严重误差 ;BEEM测试则不受影响 .随着离子轰击能量增大 ,肖特基势垒高度降低 ,且其不均匀性也越大 .用 BEEM和变温 I- V对超薄 Co Si2 /n- Si肖特基二极管的研究结果表明 ,变温 I- V测试可在一定程度上获得肖特基势垒     

Schottky barrier height modification in Au/n-type 6H-SiC structures by PbS interfacial layer

We have prepared the Au/PbS/n-6H-SiC Schottky diodes with interface layer and the reference Au/n-6H-SiC/Ni Schottky diodes without interface layer to realize Schottky barrier height (SBH) modification in the Au/SiC Schottky diodes. The BH reduction has been succeeded by the PbS interlayer to modify the effective BH by influencing the space charge region of the SiC. The PbS thin layer on the SiC was formed by the vacuum evaporation. The SBH values of 0.97 and 0.89 eV for the samples with and without the interfacial PbS layer were obtained from the forward bias current-voltage (I-V) characteristics. X-ray diffraction (XRD) study was carried out to determine the structural formation of the PbS on SiC. The reduction of the BH in the Au/PbS/n-6H-SiC Schottky diodes has been attributed to the fact that the interface states have a net positive interface charge in metal/n-type semiconductor contact, and thus the positive space charge Q_sc in the Au/PbS/n-6H-SiC Schottky diodes becomes smaller than if the interface state charges Q_ss were absent. The experimental carrier concentration value of 4.73 × 10¹⁷ cm⁻³ obtained from the forward and reverse bias capacitance-voltage characteristics for the Au/PbS/n-6H-SiC contacts is lower than the value of 5.52 × 10¹⁷ cm⁻³ obtained for the reference diode, and this is an evidence of the reduction of the BH by the modification of the space charge density of the SiC.     

A simple model for computer simulation of Schottky-barrier diodes

To simulate the electrical characteristics of metal-semiconductor Schottky barrier diodes, a numerical analysis program based on the Shockley's semiconductor equations has been established. The thermionic emissions of electrons and holes from semiconductor to metal as well as the electric field in the interfacial layer are taken as the derivative boundary conditions of the nonlinear equations. The forward and reverse current-voltage characteristics of various metal-silicon and metal-silicide-silicon Schottky barrier diodes can be simulated by properly choosing the zero-field barrier height and the interfacial-layer capacitance. The barrier height variation as a function of applied voltage is related to the space-charge density and the interfacial-layer capacitance. The nonideality of forward characteristics is attributed to the bending of majority carrier imref and the raising of barrier height. The soft behavior of reverse characteristics can be modeled in terms of the interfacial-layer capacitance.     

SiC表面氢化研究

该文提出6H-SiC ( 0001)/SiO2间过渡层的概念和过渡层结构,通过分析过渡层与HF溶液的反应机理,建立湿化学处理中的SiC表面氢化模型。模型以氢钝化SiC表面悬挂键,降低SiC表面的界面态密度,消除了费米能级钉扎,获得理想的SiC表面。将此模型用于SiC/金属接触的SiC表面处理,在100℃以下制备了理想因子n=1.2~1.25的肖特基结和比接触电阻＝510-3 cm2~710-3 cm2的SiC欧姆接触,其优点在于不仅避免了欧姆接触800~1200℃的高温合金,而且改善了肖特基接触的电学特性。SiC表面模型与实验结果吻合较好。     

Metal-germanium Schottky barriers

A systematic study has been made of the electrical characteristics of Schottky barriers fabricated by evaporating various metal films on n-type chemically cleaned germanium substrates. The diodes, with the exception of Al---Ge contacts, exhibit near-ideal electrical characteristics and age only slightly towards lower barrier height values. Al---Ge contacts exhibit very pronounced ageing towards higher barrier height values, due to formation of an extra aluminium oxide interfacial layer. Because of this, the barrier height values of aged Al---Ge contacts derived from I-V and C-V characteristics differ significantly. The dependence of the barrier height, (φ_b) on the metal work function, φ_m, for different metal-germanium contacts shows that surface states play an important role in the formation of the barrier. The density of germanium surface states is estimated to be D_s = 2 × 10¹³ eV⁻¹ cm⁻².     

Schottky diode characteristics of Ti on strained-Si

The Schottky barrier height and ideality factor of Ti on p-type strained-Si (grown on a graded relaxed Si_0.82Ge_0.18 buffer layer) were investigated in the temperature range 200–300 K using the current-voltage (I-V) characteristics and were found to be temperature dependent. While the ideality factor decreases with an increase in temperature, the barrier height increases.