氢等离子体气氛中退火多孔硅的表面和光荧光特性

用电化学腐蚀法制备了多孔硅(PS),在氢等离子体气氛中不同温度下对多孔硅样品进行了退火处理,并进行了光致发光(PL)谱和原子力显微镜(AFM)表面形貌的测量。不同退火温度给PS表面形态带来较大变化,也影响了其PL谱特性。在退火的样品中观察到的PL谱高效蓝光和紫光谱带,我们认为主要源于量子限制发光峰和非平衡载流子被带隙中浅杂质能级所俘获而引起的辐射复合所产生的。在420—450℃退火处理的多孔硅的PL谱上观察到了一个未见诸于报道的紫光新谱带(3．24eV,382nm),其发光机理有待于进一步研究。     

稀土Nd,Ce掺杂硅基薄膜光致发光特性

测量了Nd,Ce稀土离了注入Si基晶片，在不同离子注入剂量、不同退火条件下的室温光致发光（PL）谱，结果表明它们均具有蓝、紫发光峰，且发光稳定。在一定范围内发光效率随掺杂浓度的增加而增大，随退火条件的不同而改变。运用原子力显微镜（AFM）对样品的表面形貌进行了观察，结果显示，样品表面颗粒大小、粗糙度将影响其发光效率。表面颗粒大小均匀，均方根粗糙度小的样品发光效率较高。通过对样品的卢瑟福背散射（RBS）能谱测量，对样品的表面结构进行了探讨，并讨论了表面结构与光致发光特性之间的联系。对样品的发光机理作了初步探讨。     

稀土掺杂硅基薄膜的高效发光特性

测量了在不同离子注入剂量,不同退火条件下的Nd注入Si基晶片室温光致发光谱,结果表明它们均具有蓝、紫发光峰,且发光稳定。在一定范围内发光效率随掺杂浓度的增加而增大,随退火条件的不同而改变。在实验室条件下,对掺杂硅片和单晶硅片进行电化学腐蚀制成多孔硅样片,同时用适当配比的HNO3对以单晶硅为基底的多孔硅进行处理,测试了腐蚀后各类样品的光致发光（PL）谱。发现掺稀土Nd的多孔硅和用HNO3处理的多孔硅的发光效率有显著提高。     

多孔硅在30~180℃温区光致发光谱的研究

对长期存放在空气中的多孔硅样品和即时制备的多孔硅样品分别在室温~180℃下进行了光致发光（PL）温度效应的研究.两类样品的PL呈现不同的变化规律.前者的PL还表现为双峰,且长波PL峰随温度升高蓝移;后者的PL表现为单峰,且PL峰位随温度升高红移.基于量子限制效应对后者进行了解释;而前者难以用分立的量子限制和表面发光中心模型来解释,实验结果表明两种机制之间可能有较复杂的耦合效应发生.     

掺钛化学腐蚀法制备发光稳定的多孔硅

本文采用掺钛化学腐蚀法制备出了发光稳定性和均匀性都较好的多孔硅 (PS)。存放和退火试验表明 ,光致发光 (PL)谱峰位不蓝移 ,强度不衰减。多孔硅发光稳定性的提高归因于制备过程中样品表面原位氧和钛的钝化。钛的浓度和腐蚀时间对PL强度有明显影响 ,最佳钛浓度约为 0 0 8mol·L- 1 ,最佳腐蚀时间约为 2 0min。掺钛化学腐蚀法制备的PS的光激发过程符合量子限域机制 ,而其PL过程却与量子限域模型不符 ,这表明其光发射过程不是带 带直接跃迁产生的 ,即存在一个表面态     

金刚石膜/多孔硅复合材料的性能表征

提出了一种新颖的多孔硅表面钝化技术,即采用微波等离子体辅助的化学气相沉积（MPCVD）方法在多孔硅上沉积金刚石薄膜。采用原子力显微镜（AFM）、扫描电子显微镜（SEM）、X射线衍射仪（XRD）、拉曼光 谱仪和荧光分光度计对多孔硅及金刚石膜的表面形貌、结构和发光特性进行了表征。结果表明采用微波等离子体化学气相沉积法可在多孔硅基片上形成均匀、致密、性能稳定且对可见光具有全透性的金刚石膜。金刚石膜与多孔硅的复合,大大稳定了多孔硅的发光波长和强度,同时增强了多孔硅的机械强度。     

发光多孔硅表面微结构及其晶格畸变的实验研究

用电化学方法制备了不发光多孔硅和发光多孔硅,用X射线双晶衍射对两类多孔硅表面进行了微结构分析和晶体质量表征,实验表明两类多孔硅的微结构间存在着很大差别。不发光多孔硅表面对X射线的双晶衍射摇摆曲线可解叠成两个峰,它们分别来自样品多孔层和单晶硅衬底,而发光多孔硅对X射线的双晶衍射摇摆曲线呈高斯对称分布,不可解叠。发光多孔硅比不发光多孔硅表面晶体质量差,且电化学腐蚀越严重,表面晶体质量下降也越严重。     

水热腐蚀时间对铁钝化多孔硅表面形貌和光致发光的影响

采用水热腐蚀法制备了4个腐蚀时间不同的铁钝化多孔硅样品,铁钝化多孔硅样品表面呈海绵结构,随着腐蚀时间增加,样品表面的平整度下降,腐蚀孔尺寸差别有增大的趋势。在250nm光激发下,样品发光峰位于620nm附近,半峰全宽约130nm。腐蚀时间从10min增加到40min,4个样品的发光峰并未出现定向的红移或蓝移。结合样品傅里叶变换红外吸收光谱的结果,铁钝化多孔硅的光致发光行为可归因于量子限制-发光中心作用,相应的辐射复合发光中心为非桥氧空穴。     

多孔硅量子点中的电子局域态

经过激光辐照和高温退火加工能够生成多孔硅样品,在650—780 nm处检测到很强的光致荧光（PL）峰,并且有明显的钉扎和增强效应.实验表明,这种PL发光的强度与样品受辐照和退火的时间短密切相关.通过第一性原理模拟计算发现,样品表面用SiO 双键和Si—O—Si桥键钝化,能隙中会出现电子局域态.激光辐照和高温退火的时间长短决定了样品表面SiO双键和Si—O—Si桥键的密度,而该密度正是影响多孔硅量子点中电子局域态生成的关键. 关键词： 多孔硅量子点 硅氧钝化键 电子局域态     

声空化物理化学综合法制备发光多孔硅薄膜的微结构与发光特性

声空化所引发的特殊的物理、化学环境为制备高效发光的多孔硅薄膜提供了一条重要的途径.实验结果表明，声化学处理对于改善多孔硅的微结构，提高发光效率和发光稳定性都是一项非常有效的技术.超声波加强阳极电化学腐蚀制备发光多孔硅薄膜，比目前通用的常规方法制备的样品显示出更优良的性质.这种超声的化学效应源于声空化，即腐蚀液中气泡的形成、生长和急剧崩溃，在多孔硅的腐蚀过程中，孔中的氢气泡，由于超声波的作用增加了逸出比率和塌缩，有利于孔沿垂直方向的腐蚀. 关键词： 声空化方法 微结构 发光特性 多孔硅     

多孔硅光致发光峰半峰全宽的压缩

硅发光对于在单一硅片上实现光电集成是至关重要的.目前已有的使硅产生发光的方法有:掺杂深能级杂质、掺稀土离子、多孔硅、纳米硅以及Si/SiO₂超晶格.声空化所引发的特殊的物理、化学环境为制备光致发光多孔硅薄膜提供了一条重要的途径.实验表明,声化学处理对于改善多孔硅的微结构,提高发光效率和发光稳定性都是一项非常有效的技术.超声波加强阳极电化学腐蚀制备发光多孔硅薄膜,比目前通用的常规方法制备的样品显示出更优良的性质.这种超声波的化学效应源于声空化,即腐蚀液中气泡的形成、生长和急剧崩溃.在多孔硅的腐蚀过程中,由于超声波的作用增加了孔中氢气泡的逸出比率和塌缩,有利于孔沿垂直方向的腐蚀,使多孔硅光致发光峰的半峰全宽压缩到了3.8nm.     

少子寿命和表面形貌与多孔硅发光性能的关系

研究了不同时间腐蚀的多孔硅的光致发光性能与多孔硅的表面形貌和少子寿命之间的关系。结果表明,多孔硅的发光来自与氧空位有关的缺陷,而多孔硅表面的氢原子能够钝化多孔硅表面的非辐射中心从而提高多孔硅的发光效率。多孔硅的空隙度随腐蚀时间的延长而增大,这也导致了多孔硅的少子寿命的降低,从而造成多孔硅的光致发光效率随多孔硅空隙度的增大以及少子寿命的降低而提高。另外,原子力显微照片表明长时间的腐蚀使多孔硅表面层被化学腐蚀,从而降低了多孔硅表面的粗糙度。     

Enhanced physical properties of porous silicon for improved hydrogen gas sensing

In the current communication, porous silicon samples were prepared by pulsed photoelectrochemical etching using a hydrofluoric acid-based solution. The structural and gas-sensing properties of the samples were studied. Apart from the cycle time T and pause time T_off of the pulsed current, a novel parameter, in the shape of the current named ‘delay time T_d’ was introduced. Our results showed that by optimization of delay time, the porosity of samples can be controlled due to the chemical preparation of silicon surface prior to electrochemical anodization. The fourier-transform infrared measurements of porous silicon (PS) layers on Si substrate showed that the typical PS surface was characterized by chemical species like Si–H and Si–O–Si terminations. The two-minute delay before applying electrical current was considered sufficient for the fabrication of higher porosity (83%), more uniform, and more stable structures. The photoluminescence (PL) peak of the optimized sample showed higher intensity than the other samples. An obvious PL blue shift also revealed a change in the crystallographic characteristics of silicon due to quantum confinement effects. Metal–semiconductor–metal diodes with Schottky contacts of nickel were fabricated on PS samples and the potential application of optimized substrates for the improved sensitivity, stability, response time and recovery time of hydrogen gas sensors was subsequently studied.     

A novel method of fabricating porous silicon material: ultrasonically enhanced anodic electrochemical etching

Ultrasonically enhanced anodic electrochemical etching is developed to fabricate luminescent porous silicon (PS) material. The samples prepared by the new etching method exhibit superior characteristics to those prepared by conventional direct current etching. By applying ultrasonically enhanced etching, PS microcavities with much higher quality factors can be fabricated. The improved quality induced by ultrasonic etching can be ascribed to increased rates of escape of hydrogen bubbles and other etched chemical species from the porous silicon pillars' surface. This process will cause the reaction between the etchant and the silicon wafer to proceed more rapidly along the vertical direction in the silicon pores than laterally.     

Optoelectronic characterization of ZnS/PS systems

ZnS thin films are deposited on porous silicon （PS） substrates with different porosities by pulsed laser deposition （PLD）. The photoluminescence （PL） spectra of the samples are measured at room temperature. The results show that the PL intensity of PS after deposition of ZnS increases and is associated with a blue shift. With the increase of PS porosity, a green emission at about 550 nm is observed in the PL spectra of ZnS/PS systems, which may be ascribed to the defect-center luminescence of ZnS films. Junction current- voltage （I-V） characteristics were studied. The rectifying behavior of I-V characteristics indicates the formation of ZnS/PS heterojunctions, and the forward current is seen to increase when the PS porosity is increased.     

Flat layered structure and improved photoluminescence emission from porous silicon microcavities formed by pulsed anodic etching

Single-mode, highly directional and stable photoluminescence (PL) emission has been achieved from porous silicon microcavities (PSMs) fabricated by pulsed electrochemical etching. The full width at half maximum (FWHM) of the narrow PL peak available from a freshly etched PSM is about 9 nm. The emission concentrates in a cone of 10° around the normal of the sample, with a further reduced FWHM of ∼5.6 nm under angle-resolved measurements. Only the resonant peak is present in such angle-resolved PL spectra. No peak broadening is found upon exposure of the freshly prepared PSM to a He-Cd laser beam, and the peak becomes somewhat narrower (∼5.4 nm) after the PSM has been stored in an ambient environment for two weeks. At optimized etching parameters, even a 4-nm FWHM is achievable for the freshly etched PSM. In addition, scanning electron microscopy (SEM) plane-view images reveal that the single layer porous Si formed by pulsed current etching is more uniform and flatter than that formed by direct current (dc) etching, demonstrated by the well-distributed circular pores with small size in the former in comparison with the irregular interlinking pores in the latter. The SEM cross-section images show the existence of oriented Si columns of 10 nm diameter along the etching direction within the active layer, good reproducibility and flat interfaces. It is thus concluded that pulsed current etching is superior to dc etching in obtaining flat interfaces within the distributed Bragg reflectors because of its minor lateral etching. Received: 7 March 2001 / Accepted: 23 July 2001 / Published online: 30 October 2001     

Er3+、In3+等金属离子对多孔硅光致发光性质的影响

用阳极腐蚀的方法制备了多孔硅样品,用电化学方法在多孔硅中注入Ｅｒ＾３＋、Ｉｎ＾３＋等金属离子,并对注入离子后多孔硅的光致荧光光谱进行了研究,结果表明：注入Ｅｒ＾３＋及Ｉｎ＾３＋后的多孔硅在５８８ｎｍ处的妇光峰强度大大增加,同时发光峰稍有展宽。随着离子注入时间的增长,强度继续增加,但当离子溶液浓度一定时,这种增强对时间具有饱和性。     

Characterization of nanostructured CuO–porous silicon matrix formed on copper-coated silicon substrate via electrochemical etching

A pulsed anodic etching method has been utilized for nanostructuring of a copper-coated p-type (100) silicon substrate, using HF-based solution as electrolyte. Scanning electron microscopy reveals the formation of a nanostructured matrix that consists of island-like textures with nanosize grains grown onto fiber-like columnar structures separated with etch pits of grooved porous structures. Spatial micro-Raman scattering analysis indicates that the island-like texture is composed of single-phase cupric oxide (CuO) nanocrystals, while the grooved porous structure is barely related to formation of porous silicon (PS). X-ray diffraction shows that both the grown CuO nanostructures and the etched silicon layer have the same preferred (220) orientation. Chemical composition obtained by means of X-ray photoelectron spectroscopic (XPS) analysis confirms the presence of the single-phase CuO on the surface of the patterned CuO–PS matrix. As compared to PS formed on the bare silicon substrate, the room-temperature photoluminescence (PL) from the CuO–PS matrix exhibits an additional weak ‘blue’ PL band as well as a blue shift in the PL band of PS (S-band). This has been revealed from XPS analysis to be associated with the enhancement in the SiO₂ content as well as formation of the carbonyl group on the surface in the case of the CuO–PS matrix.     

Effect of surface modification by thermally oxidization and HF etching on UV photoluminescence emission of porous silicon

Photoluminescence of porous silicon (PS) is instable due perhaps to the nanostructure modification in air. The controllable structure modification processes on the as-prepared PS were conducted by thermal oxidization and/or HF etching. The PL spectra taken from thermally oxidized PS showed a stable photoluminescence emission of 355 nm. The photoluminescence emission taken from both of PS and oxidized porous silicon (OPS) samples etched with HF were instable, which can be reversibly recovered by the HF etching procedure. The mechanism of UV photoluminescence is discussed and attributed to the transformation of luminescence centers from oxygen deficient defects to the oxygen excess defects in the thermal oxidized PS sample and surface absorbed silanol groups on PS samples during the chemical etched procedure.     

蓝光发射多孔硅RTO过程中的尺寸分离效应

对用水热腐蚀技术制备的、具有蓝光发射的多孔硅样品在快速热氧化(RTO)处理前后其光致发光谱、硅纳米颗粒的大小及尺寸分布变化进行了研究.实验发现,新鲜多孔硅样品经过RTO处理后,其光致发光谱整体蓝移并由单发光峰分裂为两个发光峰;与此对应,样品中的硅纳米颗粒在整体减小的同时出现尺寸分离现象.这一结果表明,多孔硅中的短波长发射也具有强烈的尺寸相关性. 关键词：