n-GaN肖特基势垒光敏器件的电子辐照效应

本文主要研究了n型GaN肖特基紫外光敏器件(包括GaN肖特基势垒紫外探测器,GaN肖特基二极管)的电子辐照效应和失效机理,以及辐照后二极管对不同波长光的光敏特性的变化。从实验中观测到,随着辐照注量的不断增加,GaN光敏器件的击穿电压明显减小,反向漏电流逐渐增大。证实了辐照后Au/GaN间产生的界面态是引起GaN肖特基势垒光敏器件辐照失效的原因。另外,在研究辐照效应对GaN肖特基二管光敏特性的影响时观测到,经过一定剂量的辐照后,GaN肖特基二管能探测到380nm的紫外光和可见光,而在辐照以前,它是探测不到的。这说明辐照效应将导致肖特基势垒光敏器件对较长波长的吸收,使得UV探测器中可见光成分的背景噪声增加。     

Ni/4H-SiC肖特基势垒二极管的γ射线辐照效应

对制备的Ni/4H-SiC肖特基势垒二极管（SBD）进行了γ射线辐照试验,并在辐照过程中对器件分别加0和-30?V偏压.经过1?Mrad（Si）总剂量的γ射线辐照后,不同辐照偏压下的Ni/4H-SiC肖特基接触的势垒高度和理想因子没有退化,SiC外延层中的少子寿命也没有退化.辐照后器件的反向电流下降,这是由于器件表面的负界面电荷增加引起的.研究表明,辐照偏压对Ni/4H-SiC SBD的辐照退化效应没有明显的影响. 关键词： 碳化硅 肖特基 辐照效应 偏压     

GaN基肖特基势垒二极管结构优化研究进展

作为宽禁带半导体器件,GaN基肖特基势垒二极管(SBD)有耐高压、耐高温、导通电阻小等优良特性,这使得它在电力电子等领域有广泛应用。本文首先综述了SBD发展要解决的问题;然后,介绍了GaN SBD结构、工作原理及结构优化研究进展;接下来,总结了AlGaN/GaN SBD结构、工作原理及结构优化研究进展,并着重从AlGaN/GaN SBD的外延片结构、肖特基电极结构以及边缘终端结构等角度,阐述了这些结构的优化对AlGaN/GaN SBD性能的影响;最后,对器件进一步的发展方向进行了展望。     

套刻偏差对4H-SiC 浮动结结势垒肖特基二极管的影响研究

4H-SiC浮动结结势垒肖特基二极管与常规结势垒肖特基二极管相比在 相同的导通电阻条件下具有更高的击穿电压. 由p⁺埋层形成的浮动结与主结p⁺区 之间的套刻对准是实现该结构的一项关键技术. 二维模拟软件ISE的模拟结果表明, 套刻偏差的存在会明显影响器件的击穿特性, 随着偏差的增大击穿电压减小. 尽管主结和埋层的交错结构与对准结构具有相似的击穿特性, 但是当正向电压大于2 V后, 交错结构的串联电阻更大.     

Ni/Au/n-GaN肖特基二极管可导位错的电学模型

可导线性位错被普遍认为是GaN基器件泄漏电流的主要输运通道,但其精细的电学模型目前仍不清楚.鉴于此,本文基于对GaN肖特基二极管的电流输运机制分析提出可导位错的物理模型,重点强调:1)位于位错中心的深能级受主态(主要Ga空位)电离后库仑势较高,理论上对泄漏电流没有贡献; 2)位错周围的高浓度浅能级施主态电离后能形成势垒高度较低的薄表面耗尽层,可引发显著隧穿电流,成为主要漏电通道;3)并非传统N空位,认为O替代N所形成的浅能级施主缺陷应是引发漏电的主要电学态,其热激活能约为47.5 meV.本工作亦有助于理解其他GaN器件的电流输运和电学退化行为.     

势垒可调的氧化镓肖特基二极管

氧化镓作为新一代宽禁带材料,其器件具有优越的性能.本文仿真研究了n~+高浓度外延薄层对氧化镓肖特基二极管的势垒调控.模拟结果显示,当n型氧化镓外延厚度为5 nm、掺杂浓度为2.6×10¹⁸ cm^-3时,肖特基二极管纵向电流密度高达496.88 A/cm~2、反向击穿电压为182.30 V、导通电阻为0.27 mΩ·cm~2,品质因子可达123.09 MW/cm~2.进一步研究发现肖特基二极管的性能与n~+外延层厚度和浓度有关,其电流密度随n~+外延层的厚度和浓度的增大而增大.分析表明,n~+外延层对势垒的调控在于镜像力、串联电阻及隧穿效应综合影响,其中镜像力和串联电阻对势垒的降低作用较小,而高电场下隧穿效应变得十分显著,使得热发射电流增大的同时,隧穿电流得到大幅度提升,从而进一步提升了氧化镓肖特基二极管的性能.     

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.     

Ti/4H-SiC肖特基势垒二极管抗辐射特性的研究

本文采用γ射线、高能电子和中子对Ti/4H-SiC肖特基势垒二极管(SBD)的抗辐射特性进行了研究.研究发现对于γ射线和1 MeV电子辐照,-30 V辐照偏压对器件的辐照效应没有明显的影响.经过1 Mrad(Si)的γ射线或者1×l0¹³ n/cm²的中子辐照后,Ti/4H-SiC肖特基接触都没有明显退化;经过3.43×10¹⁴ e/cm²的1 MeV电子辐照后Ti/4H-SiC的势垒高度比辐照前轻微下降,这是由于高能 关键词： 碳化硅 肖特基 辐照 偏压     

GaN肖特基二极管的正向电流输运和低频噪声行为

首先测量了GaN肖特基二极管的正向变温电流-电压特性,研究了其电流输运机制,然后分析了在不同注入电流条件下的低频噪声行为.结果表明:1)在正向高电压区,热发射机制占主导,有效势垒高度约为1.25 eV;2)在正向低偏压区(V <0.8 V),与位错相关的缺陷辅助隧穿电流占主导,有效势垒高度约为0.92 eV (T=300 K);3)在极小电流(I <1μA)和极低频率(f <10 Hz)下,洛伦兹型噪声才会出现;电子的渡越时间取决于多个缺陷对电子的不断捕获和释放过程,典型时间常数约为30 ms (I=1μA);4)在更高频率和电流下,低频1/f噪声占主导;电流的输运主要受到势垒高度的随机波动的影响,所对应的系数约为1.1.     

InAs量子点在肖特基势垒二极管输运特性中的影响

在77到292K的范围内,系统研究了含InAs自组装量子点的金属-半导体-金属双肖特基势垒二极管的输运特性.随着温度上升,量子点的存储效应引起的电流回路逐渐减小.在测试温度范围内,通过量子点的共振隧穿过程在电流电压(I-V)曲线中造成台阶结构,且使电流回路随温度的上升急剧减小.根据肖特基势垒的反向I-V曲线,计算了势垒的反向饱和电流密度和平均理想因子.发现共振随穿效应使肖特基势垒在更大的程度上偏离了理想情况,而量子点的电子存储效应主要改变了肖特基势垒的有效势垒高度,从而影响了势垒的反向饱和电流密度 关键词： 自组装量子点 肖特基势垒 电流-电压特性     

ZnO薄膜肖特基二极管的研制

采用直流反应磁控溅射的方法,在Al/Si(100)衬底上沉积了ZnO晶体薄膜.利用Al和Pt作为与ZnO接触的欧姆电极与肖特基电极,制作了ZnO薄膜肖特基二极管.X射线衍射测试结果表明ZnO薄膜具有高度的c轴择优取向.原子力显微分析表明:样品表面光洁平整,晶粒尺寸约100nm,扩展电阻分析表明ZnO薄膜的厚度为0.4μm,载流子浓度为1.8×1015 cm-3,此后的霍尔测试证实了这一结果并说明ZnO的导电类型为n型.室温下的I-V测试显示ZnO肖特基二极管具有明显的整流特性.Pt与n型ZnO接触的势垒高度为0.54eV.文中的ZnO肖特基二极管为首次研制的原型器件,其性能可以通过器件结构与制作工艺的进一步优化而得到改善.     

Sulphide passivation of GaN based Schottky diodes

Wet chemical passivation of n-GaN surface was carried out by dipping GaN samples in ammonium sulphide diluted in aqueous and alcoholic solvent base solutions. Photoluminescence (PL) investigations indicated that sulphide solution effectively led to the reduction of GaN surface states. Increased band edge PL peak showed that S²⁻ ions are more active in alcohol based solvents. X-ray photoelectron spectroscopy revealed reduction in surface oxides by introduction of sulphide species. Ni/n-GaN Schottky barrier diodes were fabricated on passivated surfaces. Remarkable improvement in the Schottky barrier height (0.98 eV for passivated diodes as compared to 0.75 eV for untreated diodes) has been observed.     

Leakage current and sub-bandgap photo-response of oxygen-plasma treated GaN Schottky barrier diodes

The effect of oxygen plasma treatment on the performance of GaN Schottky barrier diodes is studied. The GaN surface is intentionally exposed to oxygen plasma generated in an inductively coupled plasma etching system before Schottky metal deposition. The reverse leakage current of the treated diodes is suppressed in low bias range with enhanced diode ideality factor and series resistance. However, in high bias range the treated diodes exhibit higher reverse leakage current and corresponding lower breakdown voltage. The X-ray photoelectron spectroscopy analysis reveals the growth of a thin GaO_x layer on GaN surface during oxygen plasma treatment. Under sub-bandgap light illumination, the plasma-treated diodes show larger photovoltaic response compared with that of untreated diodes, suggesting that additional defect states at GaN surface are induced by the oxygen plasma treatment.     

Barrier lowering and leakage current reduction in Ni-AlGaN/GaN Schottky diodes with an oxygen-treated GaN cap layer

We report on the effect of oxygen annealing for GaN surface on the Schottky barrier configuration and leakage current in Ni-AlGaN/GaN Schottky barrier diodes. After oxygen annealing, their turn-on voltage and reverse-bias leakage current characteristics are significantly improved due to a reduction in the Schottky barrier height (SBH) and suppression in the surface states respectively. Interface state density extracted from the Terman method was reduced by 2 orders of magnitude. X-ray photoelectron spectroscopy measurements show that the oxygen annealing induces Ga₂O₃ on the GaN surface. The formation of Ga₂O₃ reduces the interface state density as well as lowers the SBH through the modification of hybridized metal induced gap states.     

High-temperature current conduction through three kinds of Schottky diodes

Fundamentals of the Schottky contacts and the high-temperature current conduction through three kinds of Schottky diodes are studied. N-Si Schottky diodes, GaN Schottky diodes and AlGaN/GaN Schottky diodes are investigated by I--V--T measurements ranging from 300 to 523~K. For these Schottky diodes, a rise in temperature is accompanied with an increase in barrier height and a reduction in ideality factor. Mechanisms are suggested, including thermionic emission, field emission, trap-assisted tunnelling and so on. The most remarkable finding in the present paper is that these three kinds of Schottky diodes are revealed to have different behaviours of high-temperature reverse currents. For the n-Si Schottky diode, a rise in temperature is accompanied by an increase in reverse current. The reverse current of the GaN Schottky diode decreases first and then increases with rising temperature. The AlGaN/GaN Schottky diode has a trend opposite to that of the GaN Schottky diode, and the dominant mechanisms are the effects of the piezoelectric polarization field and variation of two-dimensional electron gas charge density.     

Diamond Schottky Contact Transit-time Diode for Terahertz Power Generation

A diamond mixed tunneling and avalanche transit-time diode is designed in this letter. Schottky contact is used in this kind of diode to reduce the contact resistance. Electrical characteristics of n-type diamond Schottky contact have been accurately investigated. Total output power of such transit-time diode is evaluated using an accurate large-signal model. The results indicate that the new type transit-time diode can operate with the frequency up to several terahertzes. The output power density is more than 1.185 MW/cm² from 1.07 to 2.12THz. About 17% improvement in efficiency is found at 2.12THz.