掺Ge ZnSe的稳恒光电导及其局域性效应

在一定的温度以下,某些半导体材料的光电导效应在激发光源撤去以后会持久地保持下去,当温度升高超过这个温度(称为淬变温度)以后,这种持续的光电导现象会消除,称为稳恒光电导现象.而且这种光电导效应具有很强的局域性.采用电学测量方法,通过测量激光照射前后电导率随温度的变化研究了掺Ge的ZnSe的稳恒光电导效应,结果发现淬变温度高达210K的稳恒光电导效应.并通过研究光电阻随光照位置变化的趋势研究了这种光电导的局域性特性,结果发现在淬变温度以上局域性随稳恒光电导消失而消失.     

Ga δ掺杂ZnSe超晶格的稳恒光电导效应

通过直接测量激光照射前后电阻随温度的变化关系,研究了Ga δ掺杂ZnSe超晶格的稳恒光电导效应。被研究的两块样品都显示了稳恒光电导效应,其中一块样品稳恒光电导的淬灭温度为120K,另一块样品的淬灭温度接近290K。描述了对这类超晶格稳恒光电导现象的测量结果,讨论了掺杂过程对光电导淬灭温度的影响。     

Gaδ掺杂ZnSe超晶格的稳恒光电导效应

通过直接测量激光照射前后电阻随温度的变化关系,研究了Ｇａδ掺杂ＺｎＳｅ超晶格的稳恒光电导效应．被研究的两块样品都显示了稳恒光电导效应,其中一块样品稳恒光电导的淬灭温度为１２０Ｋ,另一块样品的淬灭温度接近２９０Ｋ．描述了对这类超晶格稳恒光电导现象的测量结果,讨论了掺杂过程对光电导淬灭温度的影响．     

非故意掺杂n型GaN的负持续光电导现象

研究了MOCVD方法制备的非故意掺杂n型GaN薄膜的持续光电导现象.实验发现样品的光电导与入射光强有密切的关系,当入射光强由弱到强变化时,样品会依次出现正常持续光电导(PPC)、负光电导(NPC)和负持续光电导(NPPC)现象.据知,这是首次在一个样品中仅仅通过改变入射光强就可以依次产生以上现象的实验报道.通过系统的实验分析和理论研究认为,该现象形成的主要原因是材料中深能级电子陷阱和空穴陷阱共同作用的结果.     

非故意掺杂n型GaN的负持续光电导现象

研究了MOCVD方法制备的非故意掺杂n型GaN薄膜的持续光电导现象.实验发现样品的光电导与入射光强有密切的关系,当入射光强由弱到强变化时,样品会依次出现正常持续光电导(PPC)、负光电导(NPC)和负持续光电导(NPPC)现象.据知,这是首次在一个样品中仅仅通过改变入射光强就可以依次产生以上现象的实验报道.通过系统的实验分析和理论研究认为,该现象形成的主要原因是材料中深能级电子陷阱和空穴陷阱共同作用的结果.     

凝胶维度对纳米碳化硅晶须形成过程的影响

讨论了纳米碳化硅晶须的制备过程中出现的直径分布不均匀性问题。在制备纳米碳化硅晶须的实验中发现,凝胶呈现体积跃变的现象,并且发生形貌的改变,这又直接影响纳米晶体的形状,其中的原因归之于凝胶体系的局域氢键作用,称之为维度变化。结果发现,凝胶随温度跃变首先膨胀,然后又萎缩。其逆过程同样存在这一现象并呈现体积跃变迟滞。     

带隙态对辉光放电a—SiNx：H光电导的作用

研究了a-SiN_x:H中带隙态和带尾态对光电导的影响。实验结果表明:退火引起光电导响应增加,光电流谱中的肩峰在200℃退火时消失,光生载流子的复合随退火温度的变化由双分子型变为单、双分子混合型,取决于光电导的带隙随退火温度的提高而略有增加。并从光电导测量定量地给出了悬键态密度。     

用毫微秒脉冲激光研究非晶硅的光电导和光开关特性

本文用He-Ne激光和毫微秒脉冲激光作激发光源,研究非晶硅的稳态光电导和瞬态光电导,并对非晶硅的光开关效应作了初步探讨。实验发现稳态光电导随光强按幂指数规律变化;瞬态光电导的上升和下降时间在微秒量级,并随光强的增加而减小,但与外加电场的强弱无关。     

InSb薄膜磁阻效应的厚度依赖性

在12~300K的温度范围内研究了InSb薄膜(利用MBE生长)的磁阻效应随厚度的变化关系.实验发现厚的InSb薄膜只能产生半经典(∝B2)磁阻效应.而减小薄膜厚度,在薄的InSb薄膜中会更容易出现弱反局域化效应,从而造成在低温下(35K)出现了一个异常的随温度增加而迁移率降低的趋势.我们发现该弱反局域化效应可用HLN模型拟合,证明了它可能来源于二维(2-D)体系,比如InSb的界面态.     

GaAs MESFET旁栅迟滞现象与沟道电流数据采集时间的关系

采用平面选择注入隔离工艺制作 MESFET及旁栅电极 ,通过改变半导体特性测试仪的延迟时间参数 ,深入研究了不同沟道电流的数据采集时间对旁栅效应迟滞现象的影响 .发现当延迟时间超过 2 s时 ,迟滞现象基本消失 ,旁栅效应达到稳态 ,而且准静态地改变旁栅电压 ,沟道电流的变化会达到一稳定值 ,与过程无关 ,于是可以避免迟滞现象 .并从理论上解释了所发现的现象     

GaN外延材料中持续光电导的光淬灭

研究了非故意掺杂和掺Si的n型GaN外延材料持续光电导的光淬灭。实验发现非故意掺杂GaN的持续光电导淬灭程度远大于掺Si的n型GaN;撤去淬灭光后前者的持续光电导几乎没有变化,后者的却有明显减小;稍后再次加淬灭光前者的持续光电导无变化,而后者的有明显增加。我们认为两者持续光电导的形成都与空穴陷阱有关,用空穴陷阱模型解释了非故意掺杂GaN持续光电导的形成以及淬灭;认为掺Si的n型GaN的持续光电导是电子陷阱(杂质能级)和空穴陷阱共同作用的结果,并且在持续光电导发生的不同阶段其中一种陷阱的作用占主要地位。     

Persistent photoconductivity as a tool for monitoring oxide cluster concentration in silicon wafers

Many semiconductor devices rely on the so-called “denuded zone” of the silicon wafers. It is therefore essential to have a simple means to monitor the purity of this zone. It will be shown that persistent photoconductivity (PPC) can be related to the oxygen concentration in the wafer, and thus can be used to evaluate the quality of the denuded zone. A test structure was designed and the PPC measurements performed. They clearly indicate that the intensity of the PPC effect is roughly proportional to the amount of oxygen clusters in the wafer.     

立方相GaN的持续光电导

研究了金属有机物化学气相外延 (MOVPE)方法生长的非故意掺杂的立方相 Ga N的持续光电导效应 .在六方相 Ga N中普遍认为持续光电导效应与黄光发射有关 ,而实验则显示在立方 Ga N中 ,持续光电导效应与其中的六方相 Ga N夹杂有关系 ,而与黄光发射没有关系 .文中提出 ,立方相 Ga N与其中的六方相 Ga N夹杂之间的势垒引起的空间载流子分离是导致持续光电导现象的物理原因 .通过建立势垒限制复合模型 ,解释了立方相 Ga N的持续光电导现象的物理过程 ,并对光电导衰减过程的动力学作了分析 .对实验数据拟合的结果证明以上的模型和推导是与实验相符的 .     

Study of photoconductivity and persistent photoconductivity in sulphur-doped amorphous hydrogenated silicon

We report on the spectral response and intensity dependence of photoconductivity (PC) and persistent photoconductivity (PPC) in plasma-enhanced chemical vapour deposition grown sulphur-doped n-type a-Si:H films. From the intensity dependence of PC it is found that the addition of sulphur changes the recombination mechanism from monomolecular for intrinsic and low-doped films to bimolecular at a high sulphur doping level. The photo-induced metastable increase of dark conductivity in these films is found to be quite similar to that for compensated and doping-modulated a-Si:H films. The PPC effect is detectable up to an illumination temperature of at least 380 K the highest temperature used in this study. At 300 K the conduction persists at a level of one order higher than the equilibrium dark conductivity for over 10³ s after removing the excitation. The PPC in a-Si, S:H is explained in terms of the valence alternation pair model.     

The hall mobility and its relationship with persistent photoconductivity of undoped GaN

Temperature-variable Hall effect measurements have been used to investigate the electrical properties of undoped GaN, which have the electron densities on the order of mid-10¹⁶ cm⁻³ and a Hall mobility varying from <50 cm²/sV to >500 cm²/sV. We found that very strong ionized impurity scattering limits the Hall mobility of GaN. Illumination even at 77 K has very little effect on the electron density but can lead to a noticeable persistent increase of the Hall mobility. The induced persistent photoconductivity (PPC) effect is therefore related to the Hall mobility through intrinsic electrically active defects. The properties of those defects were further investigated by monitoring a transient change of resistivity after removal of illumination at different temperatures. It reveals that the recapturing process of excited electrons into illumination-neutralized defects is the mechanism responsible for the PPC effect of undoped GaN.     

Changes in Electrical Characteristics of ZnO Thin Films Due to Environmental Factors

The impact of light and controlled gas ambient on the electrical characteristics of ZnO:P grown by pulsed laser deposition (PLD) is investigated with temperature-dependent Hall-effect and photo-Hall-effect using above-bandgap light. Exposure to blue/ultraviolet (UV) light results in long-lived persistent photoconductivity (PPC) effects dominated by electron conduction. However, these persistent effects can be largely reversed by exposing the sample to a controlled ambient of dry O₂ gas. These O₂-induced changes in the electronic properties persist in vacuum up to at least 400 K. Exposure to dry N₂ gas following blue/UV light has no effect on the observed PPC characteristics. The implications of these effects on the preparation of p-type ZnO will be discussed.     

Persistent Photoconductivity in n-type GaN

The persistent photoconductivity（PPC） phenomena in n-type GaN Films grown by metalorganic chemical vapor deposition（MOCVD） have been studied. After using some testing and analysis methods, such as the double crystal X-ray diffraction（DCXRD）, the photolumineseence（PL） spectra, etc, it is found that the issue which influences PPC in n-type GaN is not relative to the dislocations and yellow band （YB）, and is caused by the doping level of Si most likely.     

Charging of deep-level centers and negative persistent photoconductivity in modulationdoped AlGaAs/GaAs heterostructures

The relaxation kinetics of persistent photoconductivity in AlGaAs/GaAs modulation-doped heterostructures due to charging of EL2-and DX-centers is investigated over a wide range of temperatures and excitation photon energies. The light-induced charging of these deep centers was found to lead to accumulation of positive and negative localized charges, which give rise to positive and negative persistent photoconductivities, respectively. These positive and negative charges are accumulated in different parts of the heterostructure. Their different characteristic times, and the different temperature dependences of these times, result in nonmonotonic time and temperature dependences of the persistent photoconductivity. Charging of EL2-centers in the GaAs buffer layer leads to negative persistent conductivity in the temperature range 180–300 K, while the negative photoconductivity observed at the temperatures below 180 K is caused by excited states of DX-centers in the n ⁺-AlGaAs. Fiz. Tekh. Poluprovodn. 33, 68–74 (January 1999)     

Dependence of GaAs:Si persistent photoconductivity on temperature and α-particle irradiation

We investigated the photoconductivity of GaAs:Si epilayer on SI-GaAs specimens. We measured the current from the time we switched on the illumination and after switching it off as a function of time at various temperatures from 250 to 330 K. A small persistent photoconductivity starts to appear from 250 K. At 330 K a clear positive persistent photoconductivity (PPPC) appears. The persistent photoconductivity increases with temperature.Then the specimens were irradiated with α-particles from an Am²⁴¹ source at 330 K.A change in persistent photoconductivity is observed from the dose of 6×10¹² particles/cm². At higher doses not only the current increases, but also the PPC duration. We try to explain these phenomena on the base of the existing theoretical models.