微纳混合结构黑硅的制备及其关键工艺技术讨论

黑硅是一种能大幅提高器件光电转换效率的新型电子材料,微纳混合结构黑硅是一种比普通黑硅材料更高效的新型黑硅材料,如何制备出大面积、形貌特征好、表面洁净度高的黑硅材料是制备高效的黑硅太阳能电池的前提。首先,利用湿法腐蚀方法,通过设计合适的反应固体装置和良好的工艺控制手段,在金字塔硅表面制备了大面积的微纳混合结构黑硅;然后,对其制备的关键工艺技术进行了研究讨论。实验结果表明,该方法制备的微纳混合结构黑硅具有形貌特征好、表面洁净度高和低表面反射率等特征。有效去除表面银沉积物后,该黑硅在300~1 100 nm范围内的加权平均反射率低至4.06%。该制备工艺方法适用于大面积高效微纳混合结构黑硅的规模制备,在高效黑硅太阳能电池领域具有重要的应用价值。     

硅太阳电池表面多孔硅的制备与作用

利用电化学方法在硅太阳能电池的金字塔上面刻蚀一层多孔硅,研究多孔硅对硅表面反射率、光电转换量子效率的影响以及氧化对不同波长的光电转换量子效率的影响。研究发现氢氟酸浓度对反射率没有明显的影响,而电化学反应时间可以调制反射率最低波长点,最终获得综合反射率低至2%的优质减反效果。多孔硅的存在使得300～500 nm的光电转换量子效率降低,500 nm以上长波的光电转换量子效率增加。氧气氛围中的快速退火能够有效降低少数载流子的表面复合,从而增加短波段的光电转换量子效率。     

飞秒激光烧蚀硅表面产生微纳结构过程中激光脉冲数目的影响

为了研究飞秒激光脉冲数目与硅表面形貌之间的关系,在相同的SF6气体氛围下,改变照射硅表面的飞秒激光脉冲数,发现在飞秒激光照射下由硅表面形成的微型锥状尖峰的高度与飞秒激光脉冲数呈现一种非线性关系.通过对该关系的研究有利于找出在制造具有较高吸收效率的高微型锥状尖峰的"黑硅"的实验条件,有利于基于"黑硅"材料的光电器件转化效...     

毫秒脉冲激光致硅光电二极管电学损伤的有限元分析及实验研究

为了研究毫秒脉冲激光致硅基PIN光电二极管电学损伤,基于热传导及弹塑性力学理论,在光电二极管内部材料各向同性并且P-I-N三层结构之间满足温度连续和热流平衡条件下,建立毫秒脉冲激光辐照硅基PIN光电二极管二维轴对称模型,采用有限元方法模拟分析了1064 nm Nd:YAG毫秒量级脉冲激光辐照硅基PIN光电二极管的温度场与应力场分布,并实验测量了硅基PIN光电二极管实验前后的电学参数.结果表明,激光辐照硅基PIN光电二极管时,温升使材料表面熔融、烧蚀,并且在空间上存在温度梯度变化,即激光辐照产生的热与应力使光敏面及硅晶格晶键损伤,最终造成光电探测器的探测性能下降.研究结果可为毫秒脉冲激光辐照硅基PIN光电二极管电学损伤机理奠定基础.     

硅纳米线阵列光电探测器研究进展

硅(Si)作为最重要的半导体材料之一,被广泛应用于太阳电池、光电探测器等光电器件中.由于硅和空气之间的折射率差异,大量的入射光在硅基表面即被反射.为了抑制这种反射带来的损失,多种具有强陷光效应的硅纳米结构被研发出来.采用干法蚀刻方案多数存在成本高昂、制备复杂的问题,而湿法蚀刻方案所制备的硅纳米线阵列则存在间距等参数可控性较低、异质结有效面积较小等问题.聚苯乙烯微球掩膜法可结合干法及湿法蚀刻各自的优点,容易得到周期性硅纳米线(柱)阵列.本文首先概述了硅纳米线结构的性质和制备方法,总结了有效提升硅纳米线(柱)阵列光电探测器性能的策略,并分析了其中存在的问题.进而,讨论了基于硅纳米线(柱)阵列光电探测器的最新进展,重点关注其结构、光敏层的形貌以及提高光电探测器性能参数的方法.最后,简要介绍了其存在的主要问题及可能的解决方案.     

基于BiFeO_3/ITO复合膜表面钝化的黑硅太阳电池性能研究

采用金属银辅助化学刻蚀法在制绒的硅片表面刻蚀纳米孔形成微纳米双层结构,以期获得高吸收率的太阳能电池用黑硅材料.鉴于微纳米结构会在晶硅表面引入大量的载流子复合中心,利用磁控溅射技术在黑硅太阳电池表面制备了BiFeO_3/ITO复合膜,并对其表面性能和优化效果进行了探索.实验制备的具有微纳米双层结构的黑硅纳米线长约180—320 nm,在300—1000 nm波长范围内入射光反射率均在5%以下.沉积BiFeO_3/ITO复合薄膜后的黑硅太阳能电池反射率略有提高,但仍然具有较强的光吸收性能;采用BiFeO_3/ITO复合膜的黑硅太阳能电池开路电压和短路电流密度分别由最初的0.61 V和28.42 mA/cm~2提升至0.68 V和34.57 mA/cm~2,相应电池的光电转化效率由13.3%上升至16.8%.电池综合性能的改善主要是因为沉积BiFeO_3/ITO复合膜提高了电池光生载流子的有效分离,从而增强了黑硅太阳电池短波区域的光谱响应,表明具有自发极化性能的BiFeO_3薄膜对黑硅太阳能电池的表面性能可起到较好的优化作用.     

石墨烯/硅肖特基太阳能电池的光电特性

以甲烷作为反应气体,利用化学气相沉积法在硅衬底表面上沉积石墨烯薄膜,制备了石墨烯/硅肖特基太阳能电池.利用原子力显微镜和拉曼光谱观察了石墨烯薄膜的表面形貌,并用紫外-可见光光谱仪和光-电流测试仪器研究了石墨烯样品和太阳电池的光电特性.实验结果表明:制备的石墨烯薄膜厚度为几个原子层,薄膜表面均匀,并具有良好的电学特性,石墨烯/硅太阳能电池的能量转换效率可达3.7%.     

硅基锗薄膜的异质外延生长及其在光电子器件中的应用

准直接带隙的锗,其禁带宽度小,吸收系数大,迁移率高,更重要的是,它能与硅微电子工艺兼容,在硅基光电集成中得到了广泛的研究和应用．文章综述了硅基锗薄膜的异质外延生长及其在光电子器件（特别是长波长光电探测器和激光器）应用上的进展;介绍了在硅衬底上异质外延生长锗薄膜的缓冲层技术,如组分变化的SiGe缓冲层技术、选区外延技术和低温技术;讨论了硅基锗薄膜光电探测器的性能与结构的关系以及发展趋势;分析了张应变和n型掺杂对锗光电性质的影响;展望了硅基锗薄膜单片集成和电抽运激光器的前景．     

飞秒激光改性6H-碳化硅晶体表面光电导增益现象研究

半绝缘6H型碳化硅(6H-SiC)具有高电阻率性质,在可见光照射下进行光电导测量时,通常光生电流很小;然而经过飞秒激光辐照改性之后,发现在可见光波段的光电导有明显的增益.本文利用紫外-可见-近红外吸收谱、X射线光电子能谱和发光光谱测量分析了激光改性之后碳化硅样品的光谱吸收、发射和晶体元素比例变化情况.分析认为碳化硅光电导增益的原因是飞秒激光辐照过程改变了碳化硅表面的硅碳元素的原子浓度比,形成新的物质结构形式,从而导致了表面光电导性能的提高.     

一种四象限光电定向装置的实现

本文采用四象限硅光电池作为光电探测接收器．根据和差式原理，设计并在实验上实验了一种四象限可直观、快速观察的光电定向装置。     

飞秒激光微构造硅光电二极管的光电响应

在一定条件SF6气体氛围中,硅可在飞秒激光辐照区产生m量级的尖峰结构。针对不同尖峰高度的微构造硅,在不同温度下退火,采用电子蒸发的方法在正反面分别镀上铝电极,制备出了飞秒激光微构造光电二极管,并测试了其光电响应。实验结果表明:飞秒激光微构造光电二极管的响应随微构造硅光电二极管的尖峰高度和退火温度的不同而不同。尖峰高度为3～4 m的样品在973 K温度退火30 min后,响应度可达0.55 A/W。即使在1100 nm波长处,这种新型的硅光电二极管的响应仍可高达0.4 A/W。     

Effect of polarization on femtosecond laser pulses structuring silicon surface

Arrays of conical-like spikes can be formed on silicon surface after irradiated with femtosecond laser pulses in ambient of SF₆ or N₂. In this article, we report our observations on how the shape of the spikes formed on silicon surface varies with the polarization of laser beam. The experimental results show that, with circular polarized laser irradiation, the shape of the spikes is conical; however, with linearly polarized laser irradiation, the spikes show elliptic conical shape, and the long-axes are perpendicular to the direction of the polarization of laser beam. The asymmetric shape of spikes produced by linearly polarized laser beam can be explained by considering the polarization dependence of Fresnel-refraction.     

不同气氛下飞秒激光诱导硅表面微结构

利用钛宝石飞秒激光脉冲对单晶硅在SF6、空气和真空环境中进行了累积脉冲辐照,研究了硅表面微结构的演化。在SF6气氛中,在激光辐照的初始阶段,硅表面形成了1维的波纹结构,随着辐照脉冲数的增加,波纹结构演化成了2维凹凸结构。累积600个脉冲后,硅表面产生了准规则排列且具有大纵横比的锥形尖峰结构。该结构呈现高度相对较低、锥形尖端小球不明显的特征,分析认为主要与环境气压的大小有关。对比空气、SF6和真空中的微结构发现,尖峰的数密度依次减小;SF6中形成的尖峰高度最大,其次为真空,再次为空气。研究结果表明,真空、SF6和空气3种环境下微结构的形成及表面形貌主要由激光烧蚀、化学刻蚀和氧化决定。     

Analysis of sunlight loss for femtosecond laser microstructed silicon and its solar cell efficiency

Black silicon, which is obtained by irradiating the surface of a Si wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas, holds great promise in the preparation of high-performance intermediate band silicon solar cells. Using a three-level model, the enhanced usefulness of sunlight of the microstructured silicon was firstly analyzed. A detailed study on the relationship between the light loss, the ionization energy of doped impurities in silicon and the impurity band width were given. Then the effect of the position of intermediate band within the forbidden gap of silicon on the theoretical conversion efficiency for the corresponding solar cell is discussed using the Detailed Balance Theory. Finally problems need to be resolved in making intermediate band solar cells based on femtosecond laser microstructured silicon are pointed out with great emphasis.     

Femtosecond-laser-induced-crystallization and simultaneous formation of light trapping microstructures in thin a-Si:H films

We report the observation of crystallization and simultaneous formation of surface microstructures in hydrogenated amorphous silicon (a-Si:H) thin films as one step laser processing. Light trapping microstructures of around 300 nm in height were formed on a-Si:H films of thickness in the range of 1.5 μm to 2 μm deposited on soda lime glass after exposure to femtosecond laser pulses. Scanning electron microscope (SEM) images show the formation of spikes that are around 1 μm part and their heights could be controlled by the laser fluences. Atomic force microscope (AFM) images were taken to study the roughness created on the surface. The mean roughness of the textured surface increases with laser fluence at smaller power densities, and for power densities beyond 0.5 J/cm² the film removal deteriorates the texturing. X-ray diffraction results indicate the formation of a nano-crystalline structure with (111) and (311) crystal orientation after the laser treatment. The observed black color and enhanced optical absorption in the near infrared region in laser treated films may be due to a combined effect of light trapping in the micro-structured silicon surface because of multiple total internal reflections, phase change in the film, possible defect sites induced after laser treatment and formation of SiO_x. Demonstration of light trapping microstructures in thin a-Si:H films and simultaneous crystallization could provide new opportunities for optoelectronic devices. PACS 42.55.Px; 42.62.Cf; 81.05.Ge     

飞秒脉冲激光辐照下硅表面光致荧光特性(英文)

采用钛宝石飞秒脉冲激光对单晶硅在空气中进行辐照,研究了硅表面在不同扫描速度和能量密度下的光致荧光特性。光致荧光谱(PL)测量表明,在样品没有退火处理的情况下,激光扫描区域观察到橙色荧光峰(603nm)和红色荧光带(680nm附近)。扫描电子显微镜(SEM)测量显示,在飞秒脉冲激光辐照硅样品的过程中硅表面沉积了大量的纳米颗粒。利用傅里叶变换红外光谱仪(FT-IR)检测到了低值氧化物SiOx(x2)的存在,并且结合能谱仪(EDS)检测结果发现氧元素在光致发光中起着重要作用。研究表明:603nm处橙色荧光峰来自微构造硅表面低值氧化物SiOx,680nm附近红色荧光带来自量子限制效应。同时样品表面硅纳米颗粒的尺寸和氧元素的浓度分别决定了红色荧光带和橙色荧光的强度,通过调节飞秒激光脉冲的扫描速度和能量密度,可以有效地控制样品的荧光强度。     

Circular ripple formation on the silicon wafer surface after interaction with linearly polarized femtosecond laser pulses in air and water environments

Ultrashort laser pulse interaction with the surface of silicon wafer in air and water environments is investigated. Ti:sapphire laser with 40 femtosecond laser pulses at 790 nm and 10 Hz repetition rate was used. The ablation threshold of the silicon surface in the air was determined to be about 0.28 J cm^?2. The surface morphology was studied by using scanning electron microscope images. The size of the regular ripples formed in the air environment is a little smaller than the laser wavelength. Due to the nonlinear interaction and self-focusing before the target, the ripples size reduced to nearly a half of the laser wavelength in the water. Moreover, the spikes’ structure formation and their diameter in air and water were studied. Two regimes for spike formation in water are proposed that can explain the anomalous decrease of the spikes’ diameter in higher fluence. During the interaction of single linearly polarized femtosecond laser pulse with the surface, an irregular ripple formation that called circular ripple is observed. This structure which is a result of radiation pressure implies to the surface by the end of the pulse. A new physical model for interpretation of the circular ripples formation based on the ponderomotive force of an ultrashort pulse laser is proposed which can predict the size of the circular ripples. The calculated results are in accordance with our experimental findings.     

Enhanced photocatalytic activity of TiO2 thin film coating on microstructured silicon substrate

Photocatalytic TiO2 thin film is prepared by sol–gel technique on microstructured silicon substrate produced by femtosecond laser cumulative irradiation. The photocatalytic activity is evaluated by the degradation of methylene blue (MB) solution under ultraviolet (UV) irradiation. For 6-ml MB solution with initial concentration of 3.0×10~-5 mol/L, the degradation rate caused by TiO2 thin film of 2-cm~2 area is higher than 70% after 10-h UV irradiation. Microstructured silicon substrate is found to enhance photocatalytic activity of the TiO2 thin film remarkably. The femtosecond laser microstructured silicon substrate is suitable to support TiO2 thin film photocatalysts.     

Microstructured silicon created with a nanosecond neodymium-doped yttrium aluminum garnet laser

We produce microstructured silicon using frequency doubled, nanosecond Nd:YAG pulses in SF₆ gas. The micro-penitentes formed are up to 20 μm tall with a sulfur concentration of 0.5% near the surface. The infrared absorption is increased to near unity and extends well below the original bandgap far into the infrared. These data are similar to results reported by others using more complicated and less economical femtosecond titanium sapphire and picosecond and nanosecond excimer lasers.     

Nd:YAG纳秒激光诱导硅表面微结构的演化

利用Nd:YAG纳秒激光(波长为532和355 nm)对单晶硅在真空中进行了累积脉冲辐照,研究了表面微结构的演化情况.在激光辐照的初始阶段,532和355 nm激光脉冲均在硅表面诱导出了波纹结构,后者辐照硅表面后形成了近似同心但稍显混乱的环形波纹结构.随着脉冲数的增加,波纹结构逐渐演化为一种类似珠形的凹凸结构,最后形成准规则排列的微米量级锥形结构,该微结构的生长依赖于表面张力波和结构自组织.分析发现,形成的交叉环形结构主要是在355 nm激光辐照硅的过程中,表面张力波导致波纹结构部分叠加的结果.