硅薄膜微结构及悬挂键缺陷研究

【作者】 黄香平；

【导师】 闻立时； 杜昊；

【作者基本信息】 中南大学 ， 物理学， 2010， 硕士

【摘要】 作为目前最具有发展前景的硅基薄膜太阳电池,具有原材料取之不尽、用之不竭、分布广泛、绿色环保以及成本低廉等优点,因此得到广泛的研究与应用。硅薄膜的结构缺陷显著影响薄膜太阳能电池的性能。硅薄膜在制备过程中往往存在晶粒间界、微空洞、悬挂键等缺陷。X射线小角散射(SAXS)已经证实了薄膜中微空洞的存在,晶界缺陷可由TEM及HR-TEM观察到,而硅薄膜中最通常的缺陷是悬挂键缺陷。悬挂键缺陷的存在对太阳电池性能的影响很大,极易成为电子和空穴的额外复合中心,使得电子的俘获截面增大、寿命下降,影响电池性能的稳定性。悬挂键中的电子是未配对的,存在自旋,电子自旋共振技术(ESR)测得在蒸发和溅射法制备非晶硅中,自旋密度达到1020 cm-3,表明悬挂键缺陷的浓度是相当高的。无掺杂的非晶硅中的悬挂键密度很高(1018cm-3或更高),电学性能很差,不能满足器件的应用要求。因此硅薄膜中悬挂键及相关缺陷的研究是十分必要的。本论文采用ECR-PECVD、ArF准分子激光晶化、中频磁控溅射等方法制备硅薄膜,采用透射电子显微镜(TEM)、X射线衍射(XRD)、喇曼光谱(Raman)、傅里叶红外光谱(FTIR)、电子自旋共振波谱(ESR)等检测手段,对薄膜的相结构、结晶状态、氢含量及悬挂键密度进行观察分析。了解硅薄膜中结晶度,氢含量及悬挂键密度对硅薄膜的影响规律,以寻求稳定化处理方法和工艺。实验结果表明,利用ECR-PECVD方法在Si基片上沉积Si薄膜,当Ar流量为70 sccm时,薄膜的悬挂键密度达到最小值4.42x 1016cm-3,且此时的氢含量也接近10 at.%,结晶度约为50%。得出最佳Ar流量值为70 sccm。本实验参数条件下,ArF激光表面处理的硅薄膜的悬挂键密度比未经过激光处理的悬挂键密度降低将近一个数量级。本实验参数下利用中频磁控溅射法在硅基片(100)及普通玻璃基片上制得硅薄膜,得出Si基片上制得的硅薄膜的悬挂键密度较普通玻璃上制得的硅薄膜的悬挂键密度低。更多还原

【Abstract】 Si-based thin film solar cells, as the most promising solar cells now, have been intensively studied and applied in many fields,because of their advantages, such as abundant storage of Si in the earth, environmental friendly characteristic, and low manufacturing cost.The thin film has been found to consist of structural inhomogeneities ralated to grain boundaries, micro-voids and dangling bonds, introduced during the prepared process of the Si films.Microstructure defects significantly affect the properties of solar cells.Small-angle X-ray scattering(SAXS)measurements have revealed the presence of micro-voids in the thin films;while grain boundary defects are investigated by TEM as well as HR-TEM. However, the most important defects in the Si films are dangling bonds.The dangling bonds, which are additional combination centers for electrons and holes, increase the capture cross section and reduce life of electrons, and consequently affect the stability of cell properties.There are spins in the un-paired electrons in dangling bonds.Electron spin resonance (ESR) investigations have revealed a very high spin density, up to 1020 cm-3,in the evaporation and sputter deposited a-Si films. The un-doped a-Si films with high density of dangling bonds(1018cm-3 or even higher) possess poor electronic quality and can not fulfill the requirement in component applications.Therefore, it is essential to investigate the dangling bonds and associated defects in the Si films.In this work, Si films were prepared or treated with three different techniques, including ECR-PECVD,ArF excimer laser crystallization and intermediate frequency magnetic sputter deposition. The phase structure, preferential orientation, crystallinity, H concentration, and dangling bond density of the as-prepared Si films were investigated with transimission electron microscope (TEM), X-ray diffreaction (XRD), Raman spectrum, Fourier transform infrared spectrum (FTIR) and electron spin resonance (ESR).The influences of crystallinity, H content, and dangling bond density on properties of Si films were analyzed, with the purpose of achieving a stabilized preparation technique.The main results are:(1)The dangling bond density in the Si films, prepared on the substrate of(100)Si plate by means of ECR-PECVD under 70 sccm Ar flow rate,is minimum of 4.42×016 cm-3,while the H concentration is-10 at.% and the crystallinity of-50%.The Ar flow rate of 70 sccm is optimum in comparison with other flow rates.(2) ArF laser surface treatment causes a reduction of dangling bond density by-1 order of magnitude, compared with un-treated Si films.(3)In the Si films prepared by intermediate frequency magnetic sputter deposition on the substrates of (100) Si and normal glass sheets, the dangling bond density is lower on the substrate of (100) Si sheet.更多还原