单晶硅表面金字塔大小及分布对少子寿命的影响

单晶硅表面钝化后少子寿命以及制成的太阳电池转换效率与单晶硅表面金字塔大小、形貌和分布密切相关。用不同的碱液刻蚀单晶硅表面,用SEM观察其表面绒面结构,测量了不同碱液刻蚀的单晶硅表面的少子寿命以及对应太阳电池的转换效率。实验研究表明,不同碱液刻蚀的单晶硅表面绒面结构形貌差异大,少子寿命明显不同。进一步研究发现,绒面上金字塔尺寸较大,且分布不均匀,则其少子寿命较短,对应太阳电池的转换效率较低;反之,绒面上金字塔小且分布均匀,则绒面少子寿命相对较长,对应的太阳电池转换效率相对较高。     

受主型杂质对p型单晶硅中少子衰减过程的影响

少子寿命测试技术是监控单晶硅中杂质和缺陷的数量及性质的重要技术手段.基于常规光电导少子寿命测试的基本参数,研究了不同性质的受主型杂质缺陷对太阳电池用p型单晶硅中少子衰减过程的影响,并重点分析了仅存在受主型电子陷阱或复合中心时,少子衰减过程的变化规律;受主型电子陷阱和复合中心并存时,少子衰减过程的变化规律.研究表明:p型单晶硅中仅存在电子陷阱或复合中心时,二者的密度和俘获截面越小,少子寿命越长,且二者均存在一个最小阈值;当二者并存时,少子电子的衰减过程可根据少子寿命值的不同分成不同的衰减区域.     

直拉区熔联合法硅单晶生长技术研究

通过直拉工艺生长直径60 mm的N型100单晶,之后以该单晶作为原料,采用区熔工艺生长成50 mm(2英寸)N型111单晶,单晶的电阻率为2.71~5.35Ω·cm,少子寿命为500~750μs,氧碳含量均低于1×16 cm-3。实验表明,通过直拉工艺和区熔工艺联合方式研制的低阻硅单晶具有电阻率控制准确、氧碳含量低、工艺易于实施等特点。同时,对直拉区熔联合法生长单晶的技术特点进行了探讨。     

施主型杂质对单晶硅中少子衰减过程的影响

单晶硅材料内少子的衰减过程可以反映出其内部杂质和缺陷的信息。针对施主型杂质是单晶硅内多数杂质呈现的基本形态,首先在小注入条件下分析了p型单晶硅内少子衰减的基本机制,然后根据施主型杂质密度、俘获截面和能级距导带底之间距离等参数的不同,重点讨论了存在施主型电子陷阱和复合中心时,太阳电池用p型单晶硅内少子衰减的基本规律。研究表明:存在施主型电子陷阱或复合中心时,p型单晶硅的少子衰减过程具有恒定的少子寿命,且杂质的密度N_T和俘获截面σ_n之积(N_T×σ_n)存在最小的影响阈值,N_T×σ_n值大于阈值的杂质和缺陷对少子衰减过程才具有重要的影响。     

高阻区熔硅单晶的径向少子寿命变化

在氩气气氛及真空环境下生长的高阻区熔硅单晶的径向少子寿命分布情况进行了检测.检测结果表明,在氩气气氛下生长的各种规格的高阻单晶,其少子寿命一般都在1 000μs以上,且径向变化大部分在10%以内,当生长工艺参数改变时,单晶少子寿命的径向分布规律虽然会有所不同,但对少子寿命径向均匀性的影响却几乎可以忽略.而在真空环境、不同工艺参数下生长的单晶,其少子寿命的径向分布及均匀性的变化则十分的明显,还会经常看到中心少子寿命400～500μs、边缘区域少子寿命高于1 000μs的单晶.本文在单晶生长试验的基础上,通过对产生这种现象的原因进行分析,确定了采用适当地降低晶体生长速率、提高加热功率的方法,可以使高阻真空区熔硅单晶中心区域的少子寿命的提高,并使其径向分布变均匀.     

3英寸半绝缘4H-SiC单晶的研制

报道了采用物理气相传输(PVT)法进行SiC单晶生长方面取得的最新进展,成功研制得到固态微波器件急需的3英寸(75 mm)半绝缘4H-SiC衬底。使用计算机模拟技术,进行了3英寸(75 mm)4H-SiC晶体生长的热场设计,并在此基础上研制出适合3英寸(75 mm)4H-SiC PVT生长的晶体生长设备,采用喇曼光谱对晶体生长表面5点进行测试,结果均为单一的4H晶型,采用非接触电阻率面分布(COREMA)方法测得晶片电阻率为109~1012Ω.cm。微管道缺陷(MPD)测量采用熔融KOH腐蚀法,测得平均微管道密度为104个/cm2,其中晶片的30%区域微管道缺陷小于10个/cm2。使用X射线双晶衍射测试得到其半高宽(FWHM)为31 arcsec,说明所获得的晶体具有良好的结晶完整性。     

硅光单体电源铝背场吸杂对非平衡少子寿命的影响

采用φ100mm厚度400μm、电阻率为0.8～2Ω·cm的p(100)CZ硅片制作硅光单体电源,并对RTP和铝背场烧结工艺进行了研究.实验发现:快速热退火工艺对硅片少子寿命产生一定影响.铝背场烧结和适当的快速热处理促成了硅片界面晶格应力对重金属杂质的吸附作用,并减少了载流子的复合中心,从而提高了光生载流子的扩散长度,提高了非平衡少子寿命.     

硅光单体电源铝背场吸杂对非平衡少子寿命的影响

采用φ100mm厚度400μm、电阻率为0.8～2Ω·cm的p(100)CZ硅片制作硅光单体电源,并对RTP和铝背场烧结工艺进行了研究.实验发现:快速热退火工艺对硅片少子寿命产生一定影响.铝背场烧结和适当的快速热处理促成了硅片界面晶格应力对重金属杂质的吸附作用,并减少了载流子的复合中心,从而提高了光生载流子的扩散长度,提高了非平衡少子寿命.     

真空高阻区熔Si单晶中的微缺陷及其少子寿命

通过在Ar气氛及真空环境中进行的高阻区熔Si单晶生长实验,分析了晶体直径、晶体生长环境及晶体生长速率对晶体中微缺陷及少子寿命的影响及产生这种影响的原因.单晶生长实验表明,与在Ar气氛下的单晶生长相比,在真空环境下采用较低的晶体生长速率即可生长出无漩涡缺陷的单晶,而当晶体生长速度较高时,尽管可以消除漩涡,但单晶的少子寿命却有明显的下降.     

坩埚位置对PVT生长AlN晶体过程中物质传输的影响

使用FEMAG晶体生长模拟仿真软件以及自主开发的PVT法有限元传质模块对全自动、双电阻加热物理气相沉积炉开展了AlN晶体生长工艺过程中不同坩埚埚位对温度场、过饱和度场及烧结体升华速率等影响的模拟仿真分析研究。模拟仿真结果表明:在给定工艺条件下,坩埚埚位较低时烧结体温度较高且内部温差较小,烧结体升华表面存在较大的Al蒸气分压梯度,各表面升华速率较快且均匀,籽晶衬底生长前沿温度场呈微凸分布,有利于晶体扩径及生长高质量晶体。随着坩埚埚位的上升,低温区向坩埚壁扩展,预烧结体内轴向及径向温度梯度增加,籽晶衬底附近径向温度梯度逐步降低,过饱和度区域扩大且增强。在坩埚埚位较高情况下,坩埚内原料升华变得不均匀,坩埚侧壁存在高过饱和区域,极易在坩埚壁上发生大量的AlN多晶沉积。模拟分析结果与大量实际晶体生长实验后的坩埚壁处沉积现象及剩余烧结体原料形态相符,较好地验证了模拟仿真分析结果的准确性。     

Origin of the low carrier lifetime edge zone in multicrystalline PV silicon

An investigation of impurities, crystal defects and microstructure has been performed on the edge zone, i.e. close to the crucible wall, which experiences reduced carrier lifetime in a directionally solidified multicrystalline p‐doped silicon ingot. The characterization methods applied have been QSSPC, FTIR, μW‐PCD, EBSD, CDI, PVScan, optical microscopy, FeB‐pair splitting and GDMS. The results of the minority carrier lifetime measurements have revealed strongly reduced values in the vicinity of the edge (< 1 μs). Increased values were obtained starting at 15–17 mm from the edge. Light elements analyses showed that the O, N and C concentrations, interstitially or in particles, did not increase in the edge zone, neither did the dislocation density. GDMS analyses detected traces of aluminium, iron, copper, titanium and chromium. The total iron concentration showed an increase towards the edge, though high concentrations were occasionally detected in the bulk. FeB pair analysis revealed large concentrations of Fe (∼1 × 10¹³ cm⁻³) in the vicinity of the edge with a distinctively decreasing trend moving away from the edge. The detected FeB‐concentrations are sufficient to account for the majority of the lifetime degradation close to the edge (0‐‐15 mm). In addition, Fe, in the form of FeB pairs, was extensively observed as object to internal gettering to high angle boundaries and dislocations. Fe, in the form of FeB pairs, is furthermore believed to originate from solid state diffusion from the crucible and coating. Copyright © 2008 John Wiley & Sons, Ltd.     

High‐quality multi‐crystalline silicon growth for solar cells by grain‐controlled directional solidification

We report simple ideas for grain control by using active cooling and crucible insulation for high‐quality multi‐crystalline silicon (mc‐Si) growth for solar cells. The method employed an active cooling spot to induce initial dendrite growth, and the solidification front was controlled to be slightly convex through crucible insulation. It was found that the percentage of grains having twins was significantly increased by the present approach. The dislocation density for those grains was also significantly lower. More importantly, the successful improvement showed that the grain size and the minority carrier lifetime increased along the growth direction. And the laser beam induced current (LBIC) measurement also showed much higher quantum efficiency for the twin area. Copyright © 2010 John Wiley & Sons, Ltd.     

垂直布里奇曼法生长CdZnTe晶体时固液界面形状的控制

采用有限元法对探测器材料 Cd Zn Te的晶体生长过程进行了热分析 ,研究了不同因素对生长过程中固液界面形状的影响 .模拟结果表明 ,当坩埚下降速度约为 1m m/ h时 ,可获得接近水平的固 -液界面 .晶体生长实验结果与计算机模拟的结论基本一致 .因此 ,通过适当选择和调节坩埚下降速度可获得高质量晶体 .     

Parameter Optimization of CdZnTe Crystal Growth Simulated by Finite Element Method

During the crystal grown by VBM, the solid/liquid interface configurations greatly influence the quality of as-grown crystals. In this paper, finite element method (FEM) was used to simulate the growth process of CdZnTe crystal. The effects of different crucible moving rates and temperature gradient of adiabatic zone on crystal growth rate and solid-liquid interface configuration were studied as well. Simulation results show that when crucible moves at the rate of about 1 mm/h, which is nearly equal to crystal growth rate, nearly flat solid/liquid interface and little variation of axial temperature gradient near it can be attained, which are well consistent with the results of experiments. CdZnTe crystal with low dislocation density can be obtained by employing appropriate crucible moving rate during the crystal growth process.     

提拉法生长钆镓石榴石(GGG)晶体

用提拉法生长出了优质的钆镓石榴石(Gd3Ga5O12)晶体,晶体尺寸达φ35 × 70mm。详细描述 了晶体生长工艺过程,讨论了生长气氛对及坩埚形状对晶体生长的影响。     

A study of the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the minority carrier lifetime of single crystal silicon processed by rapid thermal and rapid photothermal processing

Minority carrier lifetime is an efficient indicator of defect levels present in the starting material as well as process and equipment induced defects. By employing rapid thermal processing (RTP) and rapid photothermal processing (RPP) as the thermal processing techniques, we have studied the effect of ultraviolet (UV) and vacuum ultraviolet (VUV) photons on the bulk minority carrier lifetime of phosphorous doped and undoped single crystal silicon wafers. For both diffused and undiffused wafers, we have observed an enhancement in the minority carrier lifetime when UV and VUV photons are used in conjunction with the samples processed without the use of UV and VUV photons. The effect of ramp rates on the minority carrier lifetime and the significance of optimized thermal cycles have also been studied in this paper. A possible explanation based on the dependence of diffusion coefficient on the photo spectrum of light source is also given in this paper.     

Si基HgCdTe变面积光伏探测器的变温特性研究

通过变面积Si基HgCdTe器件变温I-V测试和暗电流特性拟合分析,研究了不同偏压下n-on-p型Si基HgCdTe光伏器件的暗电流成分与Si基HgCdTe材料少子扩散长度和少子寿命随温度的变化规律.在液氮温度下,随着反向偏压的增大器件的表面漏电流在暗电流中所占比重逐渐增加.在零偏压下,当温度低于200 K时材料的少子...     

Characterization of p-type multicrystalline silicon prepared by cold crucible continuous melting and directional solidification

A solar-grade boron doped silicon ingot with the cross section of 62 mm× 62 mm was cast by cold crucible continuous melting and directional solidification (CCDS). The characterization of this p-type multicrystalline silicon (mc-Si) was measured and evaluated. The results indicate that the ingot mainly consists of uniform columnar grains preferentially aligned parallel to the ingot growth direction. The average density of dislocations (N_dis) in the center area varies from 4 × 10⁴ cm⁻² to 4 × 10⁵ cm⁻², and it is much lower than that in the peripheral area. Comparing with the raw material, the oxygen concentration in the cast ingot is much lower while the carbon holds the same level. The electrical resistivity distributes uniformly and its average value is same as that of the raw material. The minority carrier lifetime (MCLT) is higher than that of the raw material and no region with obvious low MCLT is observed. CCDS has shown to be a potential process to produce mc-Si for solar cells with no crucible contamination and consumption, high production efficiency and uniform quality.