射频功率对Si薄膜微观结构及电学性能的影响

采用等离子体增强化学气相沉积(PECVD)法制备了不同射频功率的Si薄膜,并对其进行真空退火处理.研究了射频功率和退火处理对薄膜微观结构和电学性能的影响,并总结了不同电场环境对薄膜原子排列有序度的影响规律.结果表明:随射频功率的增加,Si薄膜的非晶结构无实质改变,但其少子寿命明显增强;经800℃真空退火处理后,Si薄膜的微观结构均由非晶态转变为晶态,晶化程度达60;以上,且少子寿命达到20 μs以上.     

管式PECVD氮化硅薄膜不同退火环境的工艺研究

研究了在真空与氮气两种环境中不同的退火温度和退火时间对氮化膜薄膜性能影响,测试了退火后氮化硅薄膜的膜厚、折射率、少子寿命以及电性能参数.结果表明,多晶硅管式PECVD真空退火环境优于氮气,并确定当退火温度在450 ℃、退火时间20 min时,工艺参数最佳.当温度过高过低均不利于膜厚的增加也不利于形成良好的欧姆接触,且此时光电转换效率较差.折射率的变化却不同,其最大值是在低温下达到的,此时氮气环境更有利于高折射率的获得.此外,还就膜厚和折射率随温度、环境变化的情况进行了详细的讨论.     

γ辐射及退火MgAl2O4透明陶瓷光谱特性研究

本文用不同剂量的γ射线辐照镁铝尖晶石透明陶瓷,并对辐照后的样品进行等时退火,UV-VIS和FI-IR测试表明,辐照前3360cm-1处有吸收峰,它是由V-1OH心吸收引起的.经γ辐射,样品在370nm处产生吸收带,它是由辐照产生的V型色心吸收引起的.通过退火可以使V型色心吸收带消除.结果表明:较低剂量的γ辐照能降低陶瓷紫外到红外的透过率;大剂量的γ辐照能在陶瓷中产生退火效应,能增加陶瓷红外透过率.     

退火对电子辐照氮化镓光电性能的影响

本文对10 MeV电子辐照的GaN进行了不同温度的热退火处理.用光致发光谱和霍尔测量了样品的光电性能随退火温度的变化.实验结果表明:黄光带强度、电子浓度和电子迁移率随退火温度呈非线性变化.在200～600℃退火范围内,黄光带、电子浓度和电子迁移率的变化是由于辐照Ga空位与O施主杂质的结合和断裂引起的.800℃退火后黄光带、电子浓度和电子迁移率的变化与电子辐照引入的N空位有关.     

掺Sn对定向凝固多晶硅位错及少子寿命的影响

通过微合金化获取高性能多晶硅,研究了不同Sn掺入量对定向凝固多晶硅位错及少子寿命的影响.将高纯Sn掺入到精炼冶金级硅(UMG-Si)中,定向凝固多晶硅.研究发现,硅锭位错密度沿轴向分布为中间低,底部和顶部高.在晶体硅中掺入Sn后,不影响硅的电学性能,但明显减少硅锭的位错密度.当掺入Sn含量为20 ppmw、50 ppmw和100 ppmw时,硅锭平均少子寿命由未掺Sn硅锭的0.81μs分别增加至1.22 μs、1.47 μs和1.31μs.掺Sn可减少位错密度和增加少子寿命,归因于替代位的Sn原子引入晶格应力,Sn易捕获空位V形成Sn-V对,抑制间隙原子形核.     

晶硅掺镓抑制太阳电池光致衰减效应的研究

采用掺镓晶硅和掺硼晶硅制备的寿命片和太阳电池片分别进行光致衰减实验,用WT-2000少子寿命测试仪和Halm电池电学性能测试仪等研究了它们受光照前后少子寿命和电学性能的变化.发现掺镓单晶寿命片的少子寿命衰减率比掺硼单晶寿命片低50;左右,掺镓单晶PERC电池和掺镓多晶常规电池转换效率的衰减率比掺硼单晶PERC电池和掺硼多晶常规电池分别降低3.41;和0.92;.这些结果表明晶硅太阳电池的光致衰减效应主要是晶硅中少子寿命降低导致的,晶硅掺镓后能有效抑制太阳电池的光致衰减现象.     

6H-SiC单晶的中子辐照损伤及其退火特性研究

用剂量为1.72×1019 n/cm2和1.67×1020 n/cm2的中子对掺氮6H-SiC单晶进行辐照,利用紫外-可见(UV-Vis)吸收光谱等方法研究了辐照引起的晶格损伤及随退火温度的回复过程.结果表明:中子辐照产生的大量缺陷使SiC的光吸收明显增加;光学带隙能随辐照剂量的增加而降低,这与禁带中引入的局域态缺陷能级有关.光吸收边出现强烈的连续吸收可能归因于辐照产生的不同类型缺陷簇或局部非晶区域的光散射.对两个剂量辐照的样品进行室温到1600℃的等时退火,发现两个剂量辐照产生的晶格损伤所需的退火回复温度不同,但退火回复过程都呈现出以800℃为转折点的两个相同阶段.     

降温速率对升级冶金硅定向凝固生长多晶硅少子寿命的影响

对经过前期提纯的冶金级硅料进行一次性定向凝固生长多晶硅铸锭,研究了长晶阶段降温速率对多晶硅少子寿命的影响。结果显示降温速率越低,获得多晶硅少子寿命越高,但降温速率低到一定程度时,少子寿命反而会降低。通过测试生长多晶硅硅锭曲率半径、晶体结构等数据,分析了该现象的产生原因。这将有助于升级冶金硅一次性定向凝固生长多晶硅铸锭的生产应用。     

Ca2+离子对Y3+∶PbWO4晶体辐照硬度的影响

与其它三价稀土离子(La3+、Lu3+等)掺杂相比较,Y3+的掺杂表现出特殊的低剂量辐照行为:光产额辐照后升高,同时伴随着晶体在380nm～500nm波段透过率的变化,并且辐照硬度对退火温度较敏感.以往认为光输出升高的幅度是晶体顶端大于晶体晶种端,因此推测该现象与晶体中有效分凝系数小于1的Na+、K+和Si4+等杂质有关.本文对全尺寸晶体的顶端、中段和晶种端的分段晶体测试了退火温度对晶体透过率和辐照硬度的影响,结果发现:辐照后光产额升高的现象同时存在于晶体的晶种端和晶体顶端;在一定条件下辐照后光产额升高的幅度是晶体晶种端大于晶体顶端,结合我们铅空位补偿型掺杂剂的实验结果,初步推断这可能是由于Ca2+离子含量较高而引起Y3+离子电荷补偿方式的改变.     

多孔BiFeO3薄膜的光伏效应研究

采用溶胶-凝胶法,在不同退火温度下在FTO/玻璃衬底上制备了多孔 BiFeO3薄膜并对薄膜的光伏特性进行了研究.结果表明,在450 ～600℃退火的薄膜,均呈高度(100)择优取向;所有薄膜均为多孔薄膜,450℃、500℃、550℃和600℃退火的薄膜的孔径大小分别为2 μm,2μm,6 μm和lμm.孔隙的出现与加入乙醇胺的量直接相关,同时能够增强对光的吸收.450℃、500℃、550℃和600℃退火的薄膜的光学带隙分别为2.31 eV,2.50 eV,2.51 eV,和2.62 eV,所有光学带隙显著低于通常报道的结果.450℃与500℃退火的BiFeO3薄膜具有较强的光电导效应,而600℃退火的BiFeO3薄膜具有较强的体光伏效应.BiFeO3薄膜中的体光伏效应来自铁电极化产生的内建电场.     

Growth and characterization of GaP and GaAs1−xPx

The minority carrier lifetime at low and high excitation densities was determined in VPE layers of GaP and GaAs_?0.2 P_?0.8. The lifetime at high excitation densities, having a value up to ∽350 ns, is one to two orders of magnitude larger than the lifetime at low excitation densities. It is shown that impurities are involved in some saturable killer centres dominating at low excitation densities. In the case of the largest values of the minority carrier lifetime and at a dislocation density of > 10⁵ cm^?2, the non-radiative recombination at high excitation densities is shown to occur at dislocations; at lower values of the minority carrier lifetime the killer action may be due to microprecipitates. These findings also hold for LPE layers of GaP. It is shown that by measuring the minority carrier lifetime as a function of temperature a discrimination is possible between killer action due to diffusion of minorities towards sinks like dislocations or microprecipitates and due to capture by a normal point-defect type recombination centre.     

热处理工艺对室温制备ZnO:Al薄膜结构与光电性能的影响

采用室温溅射加后续退火工艺制备了ZnO∶ Al透明导电薄膜.研究了热处理工艺对薄膜微观结构和光电性能的影响.研究表明:退火有助于减小Al~(3+)对Zn~(2+)的取代造成的晶格畸变,消除应力,促进晶粒长大,有效提高电子浓度和迁移率,降低电阻率;当溅射功率为80 W、退火温度为320 ℃时,薄膜的电阻率可低至8.6×10~(-4) Ω·cm;退火气氛对薄膜的导电性能有较大影响,真空退火可使吸附氧脱附,大大降低薄膜的方块电阻.而退火温度和退火气氛均对ZnO∶ Al薄膜的透光率没有明显影响,薄膜的透光率在86;以上.     

Anomalous Hall effect in microcrystalline Si:H films

The anomalous sign of the Hall coefficient in amorphous semiconductors is still poorly understood. It seems accepted, however, that an anomalous sign of the Hall coefficient indicates a different charge transport mechanism compared to free carrier motion on which the Lorentz force is acting. We find anomalous Hall coefficient signs in phosphorus-doped microcrystalline silicon films after irradiation with high energy electrons and subsequent annealing. These films are mixtures of amorphous and crystalline phases. We analyze measurements of Hall effect, electrical conductivity, and thermopower on such samples prior to and after electron irradiation and annealing, and use the anomalous Hall effect sign as a phenomenological indication of electronic transport in the amorphous phase. We deduce that the material consists of crystalline particles embedded in an amorphous matrix.     

电势诱导衰退和湿热衰退P-PERC太阳能电池的修复与增效

针对P型钝化发射极背面接触(PERC)太阳能电池在服役期间受到电势衰退和湿热诱导衰退影响而引起光电转换效率降低的问题,本文通过光电注入和热退火工艺对已衰退电池进行修复并研究其增效机制。实验结果表明:在光照强度为3倍标准太阳光、电注入电流为10 A、退火温度为150 ℃、工艺50 min实验条件下,对180片已衰退电池进行修复实验,其中94.32%的已衰退电池的光电转换效率得到修复,实验后电池光电转换效率平均提升8.96%。光致发光光谱和量子效率分析表明,光电注入和热退火工艺可有效减少电池因电势诱导衰退和湿热衰退形成的内部缺陷和背表面缺陷,提升衰退电池片的光电转换效率。     

Transport properties of nanocrystalline silicon and silicon–germanium

We report on the minority carrier lifetime, diffusion length and mobility in nanocrystalline Si and (Si,Ge) p⁺nn⁺ devices. The devices were fabricated on stainless steel using VHF plasma deposition techniques. Minority carrier lifetime was measured using junction reverse recovery techniques. The minority carrier lifetime was found to be well correlated with the inverse of defect density and increased with increasing measurement temperature. Simultaneous measurement of diffusion length and lifetime yielded values for hole mobility.     

Influence of defects and impurities on the deteriorated border region in multicrystalline silicon ingots

The origin of the lower minority carrier lifetime in the border region of multicrystalline silicon (mc‐Si) ingots was investigated. Based on minority carrier lifetime measurements and chemical analyses, distributions of defects and impurities were studied. It is found that the content of oxygen, carbon and other metal impurities in the border region were almost at the same level as that in the bulk, while the concentration of Fe‐B pairs is significantly higher. More interestingly, the dislocation density in the border region was observed to be much lower than that in the adjacent part. It is elucidated that the lower dislocation density in the border region leads to more iron existing in the form of Fe‐B pairs, which could be responsible for the low lifetime. In addition, it is shown that the low minority carrier lifetime in the border region can be improved effectively by phosphorous gettering. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photoelectrical properties of crystalline titanium dioxide thin films after thermo‐annealing

This paper reports the photoelectrical properties of sol gel derived titanium dioxide (TiO₂) thin films annealed at different temperatures (425‐900°C). The structure of the as‐grown film was found to be amorphous and it transforms to crystalline upon annealing. The trap levels are studied by thermally stimulated current (TSC) measurements. A single trap level with activation energy of 1.5 eV was identified. The steady state and transient photocurrent was measured and the results are discussed on the basis of structural transformation. The photocurrent was found to be maximum for the films annealed at 425°C and further it decreases with annealing at higher temperatures. The photoconduction parameters such as carrier lifetime, lifetime decay constant and photosensitivity were calculated and the results are discussed as a function of annealing temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

MOCVD growth of high-quality AlGaAs on Si substrates for high-efficiency solar cells

The crystallinity and solar cell efficiency of Al_0.22Ga_0.78As layers grown on Si substrates have been studied by varying the thermal cycle annealing (TCA) temperature. The optimum TCA temperature to obtain an Al_0.22Ga_0.78As layer with long minority carrier lifetime and high conversion efficiency has been presented. The active-area conversion efficiency of an Al_0.22Ga_0.78As solar cell on a Si substrate as high as 10.2% has been obtained under AM0 and 1 sun conditions.     

n型GaAs欧姆接触电极制备工艺

目前,n型GaAs欧姆接触电极的制备方法以蒸镀法为主,然而该方法具有设备价格高、浪费电极材料的缺点。本文采用离子溅射法制备了n型GaAs的欧姆接触电极AuGeNi/Au,通过优化制备过程,可获得表面光滑平整、成分均匀无偏析的电极层。400 ℃氩气气氛下退火处理后,电极与GaAs之间由肖特基接触变为欧姆接触,极间电阻降为原来的1/20。退火温度在400~500 ℃时可得到很小的比接触电阻率(10^-6 Ω·cm²),有利于半导体器件工作稳定性的提高,降低能耗。退火温度低于400 ℃或高于500 ℃后比接触电阻率都较大,这分别与欧姆接触未形成以及Au-Ge合金的“球聚”有关。该制备方法和过程的优点为:设备成本低、流程简便、节省电极材料,具有良好的经济效益和实用价值,适合科研实验室使用。