基于PID技术的深能级光离化截面测试方法

在分析GaN中深能级中心与入射光子问相互作用的基础上,提出了一种基于PID(prortional-integral-deriva-tive)技术的深能级中心光离化截面的测试方法.在针对分子束外延生长GaN材料的光离化截面测试中,使用该方法得到的测试结果同Klein等人报道的HEMTs器件中光离化谱吻合较好,表明基于PID技术的深能级中心光离化截面测试方法能够精确地测试GaN材料中深能级光离化截面.与现有技术相比,该方法的优点是操作方便、测试相对准确,可作为一种缺陷"指纹"鉴定的新方法应用于GaN材料的深能级研究中.     

n型LEC-GaAs中E_5能级的研究

本文采用DLTS及光电容技术对n型未掺LEC-GaAs材料中的深中心进行了研究.通过对E_5能级阈值附近光电离截面谱的温度效应的分析,提出了此能级向导带的电子发射存在两步光热激发过程的模型,算出激发态位于导带下23meV处.用多声子过程解释了E,能级光阈值能小于热激活能的现象.     

InP中钒光谱的研究

1.引言近来,人们认为钒在 InP 中起深施主的作用。这些结果是由深能级瞬时光谱(DLTS)和深能级光学光谱(DLOS)的测量而得到的。DLOS 测量结果表明处于激发态的离化施主空穴与价带共振。为了得到更精确的离化施主数据,作者对 InP:V 材料进行了光     

硅中锰施主能级Mn_i~(0/+)的光学性质研究

本文利用光电容瞬态技术,在不同温度下,首次测得了N型掺锰(Mn)硅中与Mn相关的Mn施主能级Mn_i~(o/+)(Ec-0.416eV)的绝对电子光电离截面谱图.对实验点的理论拟合表明:电子光电离截面(σ_n~o)可用简单的、作了修正的Lucovsky公式来描述.该能级的空穴光电离截面(σ_p~o),在实验系统灵敏度范围内,未检测到讯号.这意味着σ_p~o的极大值也不大于10~(-21)cm~2.该中心的热激活能E_t和电子的光电离截面闽值能量E_(10)的很好一致,以及σ_n~o不依赖于温度的实验事实说明了电子通过该能级跃迁时,不存在着同晶格的强耦合作用.     

硅中金受主能级特性的低温动态光伏研究

本文采用统计方法,对40K下金过补偿的P型硅单晶的动态光伏问题进行处理.计算结果与实验符合很好,从而探讨了硅中金受主能级在光离化、载流子复合过程中的行为,进而估算了金受主能级在hv=0.63eV光照下的光离化截面σ_i=6×10~(18)cm~2,及其对自由空穴的俘获截面σ_p=4×10~(15)cm~2.     

退火对离子注入GaN产生的深能级的影响

我们最近报道了大剂量Al+注入原生GaN后对其光学性质的影响。表明Al+的注入可能产生了某种深能级电子陷阱 ,由于电子陷阱俘获导带电子 ,导致发光猝灭。而经一定条件的退火处理 ,可使深的电子陷阱发生变化 ,因而与缺陷间的跃迁相关的黄色荧光可得到一定程度的恢复。由于注入样品的电阻率高达 1 0 1 2 Ω·cm ,因此不能用已有的常规方法测量。我们为此发展了一种称为“光增强电流谱”(PSCS)新方法 ,用于测量高阻样品中的深能级。研究发现 ,在经过快速退火处理的样品中 ,不能消除由于注入产生的准连续深能级带 ;而在某种常规条件退火的样品中 ,发现了 5个位于导带下 1 .77eV ,1 .2 4eV ,1 .1 6eV ,0 .90eV和 0 .86eV的深电子陷阱 ,它们都是Al+注入经退火后形成的稳定结构。实验发现退火使注入产生的准连续深能级带转变为独立的深能级结构 ,虽不能使GaN的本征发光得到恢复 ,但对黄色荧光的恢复是有利的。此研究有助于了解退火处理对离子注入的GaN的电学结构与发光产生的影响。PSCS的意义在于它适用于测量一切高阻半导体样品中与非辐射跃迁相联系的深陷阱能级 ,而不仅仅适用于测量Al+注入GaN产生的深陷阱能级     

离化吉布斯自由能是远比离化焓为好的表征深能级在禁带中位置的参量

通常用各种结谱方法求得的深能级激活能实际上是在测量温度范围内的平均离化焓.本文通过对作者最近观测到的两个硅中与铜有关的深能级E_1和E_2以及硅中金受主能级的仔细分析,指出它们的离化吉布斯自由能与离化焓之间存在显著的差别,如果用离化焓来表征它们在禁带中的位置,是不精确的,特别是对于硅中与铜有关深能级E_1这种表征还会导致物理上的错误结论.强调指出对于半导体中深能级来说,离化吉布斯自由能才能确切表征各个温度下它们在禁带中的位置.     

InP中的深能级杂质与缺陷

综述了近年来关于InP中深能级缺陷和杂质的研究工作。讨论了深能级杂质及缺陷对InP材料性能的重要影响;介绍了深能级瞬态谱(DLTS)、光致发光谱(PL)、热激电流谱(TSC)、正电子寿命谱(PAS)、正电子深能级瞬态谱(PDLTS)等几种研究深中心的方法在研究InP时的某些特点;综合深能级缺陷和电学性质的测试结果,证明了半绝缘InP单晶材料的电学性能、热稳定性、均匀性等与材料中一些深能级缺陷的含量密切相关;分析了对掺铁和非掺退火两种半绝缘InP材料中深能级缺陷对电学补偿的影响;评述了对InP中的一些深中心所取得的研究成果和半绝缘InP的形成机理。     

GaN基光发射二极管中深能级研究

利用深能级瞬态谱 (DLTS)仪对 Si C衬底上 Ga N基光发射二极管 (LED)中 n-In0 .2 5Ga0 .75N层的深能级进行了研究。在 77K到 3 0 0 K的温度扫描范围内只测量到一个 DLTS峰。该 DLTS峰在反向偏压为 3 V时有一极大值 ,说明 n-In0 .2 5Ga0 .75N层此时全部被耗尽。改变测量的率窗 ,得到该深能级在导带下 0 .2 4e V处 ,浓度为 2 .2 % ND,俘获截面为 1 .93× 1 0 - 1 5cm2。在 Ga N材料中 ,其他小组也报道了此位置上的深能级结果。结合文中的工作 ,该深能级可能和 n-In0 .2 5Ga0 .75N层中的线位错有关。     

调制掺杂Al_xGa_(1-x)As/GaAs异质结持久光电导的光谱响应

本文在77 K下研究了调制掺杂 n-Al_(0.3)Ga_(0.7)As/GaAs异质结持久光电导的光谱响应.结果表明,掺 Cr GaAs衬底中Cr深能级上电子的激发和 Al_xGa_(1-x)As中DX中心的光离化都产生持久光电导.     

Photoionization of deep impurity centers in quantum well structures

The absorption of light by photoionization of deep impurity centers in quantum well heterostructures is studied theoretically using a model with a maximally localized potential. Analytic expressions are found for the photoionization cross sections for light polarized perpendicular and parallel to the axis of the structure, disregarding the effect of the impurity potential on the continuum electronic states. The dependence of the frequency variation of the cross section on the charge state of the impurity after photoionization, as well as on the position of the impurity in the structure and the doping profile, is studied qualitatively near the absorption threshold. Fiz. Tekh. Poluprovodn. 33, 451–455 (April 1999)     

The photoionization cross sections of the Rg*2[3Σ+u] excimer states for Ne*2, Ar*2, and Kr*2

Based on the recently determined Rydberg series of the³Sigma+_{u}excimer states of Ne*2, Ar*2and Kr*2, the photoionization cross sections of these molecules are calculated using a single-channel quantum defect method. These cross sections are found to differ considerably from those of the asymptotic metastable atomic Rg*(ns^{3}P_{2}) states, but are in good agreement with recently reported experiments at isolated wavelengths. The implications of these results for VUV and XUV lasers are discussed.     

Characterization of deep levels in Pt-GaN Schottky diodes depositedon intermediate-temperature buffer layers

Gallium nitride (GaN)-based Schottky junctions were fabricated by RF-plasma-assisted molecular beam epitaxy (MBE). The GaN epitaxial layers were deposited on novel double buffer layers that consist of a conventional low-temperature buffer layer (LTBL) grown at 500°C and an intermediate-temperature buffer layer (ITBL) deposited at 690°C. Low-frequency excess noise and deep level transient Fourier spectroscopy (DLTFS) were measured from the devices. The results demonstrate a significant reduction in the density of deep levels in the devices fabricated with the GaN films grown with an ITBL. Compared to the control sample, which was grown with just a conventional LTBL, a three-order-of-magnitude reduction in the deep levels 0.4 eV below the conduction band minimum (E_c) is observed in the bulk of the thin films using DLTFS measurements     

Photoionization of impurity atoms in semiconductors in the presence of an applied electric field

An analytic expression for the photoionization cross section of an impurity atom in an applied field is derived for photon energies below the zero-field photoionization threshold. The use of a quantum defect wave function for the impurity ground state permits impurity atoms to be conveniently characterized in terms of known ground state energies. The Coulomb Green's function and the WKB approximation in parabolic coordinates are used to calculate the wave function of photoexcited electrons or holes from which the photoionization cross section is obtained. The results apply to shallow or deep levels associated with carriers bound to charged impurity centers. Results for photodetachment of carriers bound to neutral impurities are obtained in the limit where the impurity charge goes to zero.     

高精度智能PID控制

讨论了一种基于专家知识智能PID控制算法，根据专家知识与现场经验，实时修正PID参数。并根据系统响应的在线(识)别进行知识调整．从而实现色谱仪所要求的高精度的温度控制。此种法将在以后的高精度PID非线性控制系统的实际应用中有一定的参考价值。本文介绍了工业色谱仪智能PID温控系统的功能，并详细介绍了系统的硬件结构、软件设计及抗干扰措施。     

The nature of the deep levels responsible for photoelectric memory in GaAs/AlGaAs multilayer quantum-well structures

The electron capture parameters and photoionization cross section of the unintentional deep levels, which are responsible for photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures, have been found from an analysis of the kinetics of the excess current during and after optical illumination of these structures. The dependence of the photoionization cross section on the photon energy, the capture cross section, and the energy barrier for capture of an electron from the bottom of the conduction band indicate that the unintentional deep levels are DX centers formed by the silicon impurity. These DX centers probably appear during growth of the structures as a result of silicon diffusion from the quantum wells along as-grown defects. Fiz. Tekh. Poluprovodn. 32, 1213–1218 (October 1998)     

温度传感器动态性能的改善方法

为了对温度传感器的动态性能进行改善,使温度传感器的响应速度满足快速反应的温度测量系统的要求,在分析了常用的几种改善方法和模糊控制方法的基础上,提出了在温度测量系统中加入PID控制(比例、积分、微分控制),并用仿真工具Simulink(MATLAB的仿真集成环境)进行仿真.仿真结果表明,应用PID控制法可使温度传感器的响应时间极大地缩短,能达到改善温度传感器动态性能的目的.     

Light Effect in Photoionization of Traps in GaN MESFETs

Trapping of hot electron behavior by trap centres located in buffer layer of a wurtzite phase GaN MESFET has been simulated using an ensemble Monte Carlo simulation.The simulated results show the trap centres are responsible for current collapse in GaN MESFET at low temperatures.These electrical traps degrade the performance of the device at low temperature.On the opposite,a light-induced increase in the trap-limited drain current results from the photoionization of trapped carriers and their return to the ...     

Photoionization and photoabsorption characteristics of laser seed compounds

Measurements are reported on the photoabsorption cross sections and photoionization yields of N,N-dimethylaniline, triethylamine, trimethylamine, and tri-n-propylamine over the wavelength region from 116 nm to near the respective ionization thresholds. The usefulness of these organic compounds for UV-preionized lasers is evaluated. The characteristics of nitric oxide as a seedant are compared with those of the organic seedants. N,N-dimethylaniline was found to have the most uniform cross section and highest overall yield.