Study of the electrical and optical properties of silicon containing oxygen precipitates

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤10⁹ cm^?3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.     

Dislocation-related luminescence in Er-implanted silicon

The behavior of luminescence spectra and structural defects in single crystal Czochralski silicon after erbium implantation at 1–1.8 MeV energies and 1×10¹³ cm⁻² dose with subsequent annealing at 1000–1200°C for 0.25–3 h in argon and a chlorine-containing ambience (CCA) was studied by photoluminescence (PL), transmission electron microscopy and chemical etching/Nomarski microscopy. We have found that annealing in CCA gives rise to dislocation loops and pure edge dislocations with dominant dislocation-related lines in the PL spectrum. Pure edge dislocations are responsible for the appearance of the lines.     

Microstructure and optical properties of ZnO/porous silicon nanocomposite films

In this study, porous silicon (PS) templates were formed by electrochemical anodization on p-type (100) silicon wafer and ZnO films were deposited on PS substrates using radio frequency (RF) reactive magnetron sputtering technique. The effects of oxygen partial pressures of growth ZnO films and annealing ambience on the microstructure and photoluminescence (PL) of the ZnO/PS nanocomposite films were systematically investigated by X-ray diffraction and fluorescence spectrophotometry. The results indicated that all ZnO/PS nanocomposite films were polycrystalline in nature with a hexagonal wurtzite structure and the (002) oriented ZnO films had the best crystal quality under O₂:Ar ratio of 10:10 sccm and annealing in vacuum. PL measurements at room temperature revealed that ZnO/PS nanocomposite systems formed a broad PL band including the blue and green emissions from ZnO and red-orange emission from the PS. The mechanism and interpretation of broadband PL of the nanocomposites were discussed in detail using an oxygen-bonding model in PS and a native defects model in ZnO.     

Specific features in the generation and motion of dislocations in heat-treated silicon wafers

The specific features in the generation and motion of dislocations in silicon single-crystal wafers after different heat treatments are investigated by the four-point bending technique. It is demonstrated that annealing of silicon single-crystal wafers at a temperature of 450°C leads to their substantial hardening as compared to the postgrowth state. The oxygen-containing precipitates and precipitate dislocation pileups formed in the silicon wafer bulk during multistage heat treatment are efficient heterogeneous nucleation sites of dislocations under the action of thermal or mechanical stresses. It is found that the multistage heat treatment of the silicon wafers under conditions providing the formation of an internal getter within their bulk results in considerable disordering of the wafer structure. The inference is made that the formation of the defect state in the crystal lattice of silicon and the strength characteristics of silicon wafers substantially depend on the temperature-time schedules of the low-temperature stage of multistage heat treatment.     

Thermal annealing dependence of some optical properties of plasma-modified porous silicon

The photoluminescence and reflectance of porous silicon (PS) with and without hydrocarbon (CH_x) deposition fabricated by plasma enhanced chemical vapour deposition (PECVD) technique have been investigated. The PS samples were then, annealed at temperatures between 200 and 800 °C. The influence of thermal annealing on optical properties of the hydrocarbon layer/porous silicon/silicon structure (CH_x/PS/Si) was studied by means of photoluminescence (PL) measurements, reflectivity and ellipsometry spectroscopy. The composition of the PS surface was monitored by transmission Fourier transform infrared (FTIR) spectroscopy. Photoluminescence and reflectance measurements were carried out before and after annealing on the carbonized samples for wavelengths between 250 and 1200 nm. A reduction of the reflectance in the ultraviolet region of the spectrum was observed for the hydrocarbon deposited polished silicon samples but an opposite behaviour was found in the case of the CH_x/PS ones. From the comparison of the photoluminescence and reflectance spectra, it was found that most of the contribution of the PL in the porous silicon came from its upper interface. The PL and reflectance spectra were found to be opposite to one another. Increasing the annealing temperature reduced the PL intensity and an increase in the ultraviolet reflectance was observed. These observations, consistent with a surface dominated emission process, suggest that the surface state of the PS is the principal determinant of the PL spectrum and the PL efficiency.     

Accelerated oxygen precipitation in fast neutron irradiated Czochralski silicon

Annealing effect of the oxygen precipitation and the induced defects have been investigated on the fast neutron irradiated Czochralski silicon （CZ-Si） by infrared absorption spectrum and the optical microscopy. It is found that the fast neutron irradiation greatly accelerates the oxygen precipitation that leads to a sharp decrease of the interstitial oxygen with the annealing time. At room temperature （RT）, the 1107cm^-1 infrared absorption band of interstitial oxygen becomes weak and broadens to low energy side. At low temperature, the infrared absorption peaks appear at 1078cm^-1, 1096cm^-1, and 1182cm^-1, related to different shapes of the oxygen precipitates. The bulk microdefects, including stacking faults, dislocations and dislocation loops, were observed by the optical microscopy. New or large stacking faults grow up when the silicon self-interstitial atoms are created and aggregate with oxygen precipitation.     

Visible photoluminescence of co-sputtered Ge–Si duplex nanocrystals

The photoluminescence (PL) characteristics of co-sputtered Ge–Si duplex nanocrystal films were examined under excitation by a 325-nm HeCd laser, combined with Raman and Fourier-transform infrared reflection spectra analysis. A broad visible PL spectrum from the as-deposited Ge–Si nanocrystal films was observed in the wavelength range 350–700 nm. Basically, the PL spectrum can be considered to consist of two distinct parts originating from different emission mechanisms: (i) the spectrum in the range 350–520 nm, consisting of characteristic double peaks at 410 and 440 nm with PL intensities decreasing after vacuum annealing, probably due to vacancy defects in Si nanocrystals; and (ii) the spectrum in the range 520–700 nm, consisting of a characteristic peak at 550 nm with a PL intensity not affected by vacuum annealing, probably due to Ge-related interfacial defects. No size dependence of PL peak energy expected from quantum confinement effects was observed in the wavelength range investigated. However, with an increase of crystal size, the PL peak intensity in the blue zone decreased. The PL intensity is found to be strongly affected by silicon concentration. A film heated in air has a different PL mechanism from the as-deposited and vacuum-annealed films. PACS 78.67.Bf; 81.05.Cy; 81.15.Cd     

Correlation between impurities in Fe-Si amorphous layers synthesized by Fe implantation and photoluminescence property of β-FeSi2 precipitates in Si

Completely amorphous Fe-Si layers are formed by Fe implantation into Si substrate at a dosage of 5×10¹⁵ cm⁻² using a metal vapor vacuum arc (MEVVA) ion source under 80 kV extraction voltage and cryogenic temperature. After thermal annealing, β-FeSi₂ precipitates are formed in Si matrix. The influence of impurities in these amorphous Fe-Si layers on the photoluminescence (PL) from β-FeSi₂ precipitates is investigated. PL is found to be significantly enhanced by optimizing the impurity concentration and annealing scheme. After 60 s of rapid thermal annealing (RTA) at 900 °C, β-FeSi₂ precipitates in medium boron-doped Si substrate give the strongest PL intensity without boron out-diffusion from them.     

Cd1-xZnxTe晶体退火条件的选择及Zn压对退火晶体质量的影响

采用传统Bridgman方法和加入accelerated crucible rotation technique的Bridgman(缩写为ACRT-B)方法生长的Cd_1-xZn_xTe(x=0.04)晶体中存在有点缺陷、位错、杂质和Te沉淀等缺陷.为了减少甚至消除这些缺陷,必须将生长后的CdZnTe晶片在Cd气氛下退火.从Cd-Te和Cd_0.96Zn_0.04Te的PT相图出发,详细讨论了CdZnTe晶体的气固平衡条件,并 关键词： 1-xZn_xTe')" href="#">Cd_1-xZn_xTe 退火 气-固平衡     

Evolution of CoSi2 buried structures created by high temperature Co+ ion implantation into Si(1 0 0) during post-implantation annealing

The evolution of buried structures of cobalt disilicide, which are formed in a Si(1 0 0) matrix by 400 keV Co⁺ ion implantation at 875 K substrate temperature with subsequent rapid thermal annealing at 1275 K was studied by cross-sectional transmission electron microscopy (X-TEM). The analysis of identical samples with successive variations of the implanted doses and annealing times allows a detailed observation of the role of defects, created by the ion flux, on the process of ripening and growth of CoSi₂ precipitates. We found that transport of the implanted material along diffusive links leads to the formation of a secondary CoSi₂ distribution between the main layer and the surface. Post-implantation annealing results in the evolution of defects into dislocations, which affects the mobility and therefore the growth of CoSi₂ precipitates. Increasing the annealing time leads to the separate growth of precipitates in each layer. The result is not the formation of a single uniform buried layer because the distance between the individual layers is too large due to a screening effect, which operates during the ripening stage.     

Behavior of dislocations in silicon in the presence of mechanical and magnetic perturbations

Various types of dislocation stoppers are identified and their basic parameters are determined. Using dislocation loops as an example, the effect of internal stresses on the motion of linear defects in n-and p-Si in the field of external elastic forces is estimated. It is found that preliminary magnetic treatment of silicon plates activates the dislocation transport. In the absence of external mechanical loads, displacement of dislocation half-loops (30–50 μm) in the nonuniform field of internal stresses in a silicon crystal with a scratch (stress concentrator) is detected experimentally during isothermal annealing for 0.5–3 h at a temperature of 600–700°C. Dislocation transport is described taking into account the intrinsic (lattice) potential barrier of the crystal and two types of stoppers on the basis of magnetosensitive point defects (dopant) and “forest” dislocations. A kinetic model is proposed for describing the magnetostimulated variation of the mobility of linear defects associated with the formation of long-lived complexes with a paramagnetic impurity. It is found experimentally that the velocity of dislocations in n-and p-Si increases by a factor of 2 and 3, respectively, upon treatment of the semiconductor in a magnetic field B=1 T for 5–45 min. The “magnetic memory” effect in silicon containing dislocations is detected and kinetic aspects of the effect under natural conditions of sample storage after the removal of the magnetic field are considered. Partial velocities of dislocations and their delay times at various types of stoppers are calculated from the matching of experiment with theory.     

Nanocrystal and interface defects related photoluminescence in silicon-rich Al2O3 films

In this study, silicon nanocrystal-rich Al₂O₃ film has been prepared by co-sputtering a silicon and alumina composite target and subsequent annealing in N₂ atmosphere. The microstructure of the film has been characterized by infrared (IR) absorption, Raman spectra and UV-absorption spectra. Typical nanocrystal and interface defects related photoluminescence with the photon energy of 1.54 (IR band) and 1.69 eV (R band) has been observed by PL spectrum analysis. A post-annealing process in oxygen atmosphere has been carried out to clarify the emission mechanism. Despite the red shift of the spectra, enhanced emission of the 1.69 eV band together with the weak emission phenomenon of the 1.54 eV band has been found after the post-annealing. The R band is discussed to originate from silicon nanocrystal interface defects. The IR band is concluded to be a coupling effect between electronic and vibrational emissions.     

Electronic states at dislocations and metal silicide precipitates in?crystalline silicon and their role in?solar cell materials

Predominant dislocation types in solar silicon are dissociated into 30°- and 90°-partials with reconstructed cores. Besides shallow 1D-band localized in their strain field and a quasi-2D band at the stacking fault connecting the two partials, the existence of several intrinsic core defects with deep lying levels has been demonstrated by electron spin resonance. The majority of core defects occur in nonequilibrium situations and, with the exception of a small EPR-signal assigned to a reconstruction defect, vanish after careful annealing above 800°C. There is good evidence now that part of deep levels observed in dislocated silicon is associated with impurities, especially with transition metal impurities. Electron-hole-pair recombination at a dislocation mainly runs via its shallow bands and is strongly increased by impurities bound to its core or in the strain field. The concentration of these impurities can be reduced by gettering processes to such a low level that radiative recombination at dislocations yields a luminescence efficiency of 0.1% at room temperature. A quite coherent picture has emerged for metal impurity precipitation in silicon. Early stages of precipitation in defect-free silicon are characterised by kinetically selected metastable defects forming as a result of large chemical driving forces for precipitation. Such defects are associated with deep level spectra which show the properties of extended multielectron defects. The evolution of the system to energetically more favourable configurations proceeds via ordinary particle coarsening but also via internal ripening, a process reminiscent of the above-mentioned metastable defects. Electronically, the defects evolve into metal-like inclusions which in general seem to act as strong recombination centers for minority carriers. In the presence of dislocations metastable defects quickly transform into equilibrium structures in the course of precipitation or do not form at all. In the presence of several metal impurities silicide precipitates which can be described as solid solutions of the respective metal atoms are observed, which is at least qualitatively in accord with ternary phase diagrams. Like single-metal silicide precipitates, strong minority carrier recombination is also typical for those multi-metal silicide particles.     

液封坩埚下降法生长非掺杂InP单晶的特性研究

用液封坩埚下降(LE-VB)法沿〈100〉晶向成功地生长了非掺杂InP单晶。LE-VB晶体的4.2K光致发光谱包含束缚于中性浅受主上的激子发光、与Zn受主相关的施主-受主(DA)对发光及其声子伴线、以及与本征缺陷等有关的深能级发光三部分。通过与液封直拉(LEC)生长的籽晶的光致发光谱比较表明,在LE-VB晶体中,束缚于中性浅受主上的激子发光与籽晶中的相差不大;DA对发光的晶格弛豫比籽晶中的小;与本征缺陷等有关的深能级发光强度比籽晶中的弱。晶体的室温光致发光谱仅包含带-带发光,其发光强度形貌测试结果表明,LE-VB晶体的带-带发光强度比LEC籽晶的强。用Huber法对晶片腐蚀的结果表明,在LE-BV晶体中,位错密度仅为LEC籽晶中的三分之一。分析认为,在LE-VB晶体中,本征缺陷和位错等浓度较低,可能是其带-带发光强度比在LEC籽晶中强的物理起因。     

镶嵌在氧化硅薄膜中纳米晶硅的可见光荧光谱与发光机制的研究

采用对非晶氧化硅薄膜退火处理方法，获得纳米晶硅与氧化硅的镶嵌结构．室温下观察到峰位为2.40eV光致发光．系统地研究了不同退火温度对薄膜的Raman谱、光荧光谱及光电子谱的影响．结果表明，荧光谱可分成两个不随温度变化的峰位为1.86和2.30eV的发光带．Si2p能级光电子谱表明与发光强度一样Si⁴⁺强度随退火温度增加而增加．Si平均晶粒大小为4.1—8.0nm，不能用量子限制模型解释蓝绿光的发射．纳米晶硅与SiO₂界面或SiO₂中与氧有关的缺陷可能是蓝绿光发射的主要原因 关键词：     

Structural and photoluminescence properties of Si nanoclusters obtained by ion implantation into Si3N4 films

In the present paper we report structural and photoluminescence (PL) results from samples obtained by Si implantation into stoichiometric silicon nitride (Si₃N₄) films. The Si excess was introduced in the matrix by 170 keV Si implantation performed at different temperatures with a fluence of Φ=1×10¹⁷ Si/cm². The annealing temperature was varied between 350 and 900 °C in order to form the Si precipitates. PL measurements, with a 488 nm Ar laser as an excitation source, show two superimposed broad PL bands centered around 760 and 900 nm. The maximum PL yield is achieved for the samples annealed at 475 °C. Transmission electron microscopy (TEM) measurements show the formation of amorphous nanoclusters and their evolution with the annealing temperature.     

Cu(In,Ga)Se2太阳能电池快速热退火效应

利用光致发光（PL）分析快速热退火对Cu(In,Ga)Se2 (CIGS)电池的影响,研究退火对薄膜缺陷的影响。Cu(In,Ga)Se2电池的PL谱中总共有 7个峰,即2个可见波段峰和5个红外波段峰。退火温度较低,可减少薄膜体内缺陷,提高载流子浓度,改善薄膜质量;退火温度过高,则会引起正常格点处元素扩散,元素化学计量比改变,体内缺陷增加,吸收层带隙降低,反而会对CIGS薄膜造成破坏。     

水蒸气退火多孔硅发光性能的正电子谱学研究

使用正电子湮没寿命谱和正电子寿命-动量关联谱对水蒸气和真空条件下退火的多孔硅样品的微观缺陷结构进行表征,结合发射光谱测量结果,对影响多孔硅发光性能的因素进行了讨论.实验结果表明,水蒸气退火后样品孔壁表面的悬挂键减少,并出现新的E′γ和EX类缺陷.水蒸气退火后样品中两种缺陷数量发生变化是导致多孔硅样品发光增强的直接原因;真空退火未使样品中发光相关缺陷发生变化,样品的发光性能没有显著改变.     

Visible photoluminescence from silicon nanoclusters embedded in silicon nitride films prepared by remote plasma-enhanced chemical vapor deposition

The photoluminescence (PL) of silicon nanoclusters embedded in silicon nitride films grown by remote plasma-enhanced chemical vapor deposition at 200 °C, using mixtures of SiCl₄/H₂/Ar/NH₃ is investigated. It was found that the color and the intensity of the PL of the as-grown samples depend on the H₂ flow rate, and there is an optimum flow for which a maximum luminescence is obtained. A strong improvement of the PL intensity and change in color was obtained with annealing treatments in the range of 500–1000 °C. The changes in the composition, structure and optical properties of the films, as a function of H₂ flow rate and thermal treatments, were studied by means of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, ellipsometry and ultraviolet–visible transmission measurements. We conclude that the PL can be attributed to quantum confinement effect in silicon nanoclusters embedded in silicon nitride matrix, which is improved when a better passivation of the nanoclusters surface is obtained.     

Scanning infrared microscopy investigation of copper precipitation in cast multicrystalline silicon

The behavior of copper precipitation in cast multicrystalline silicon (mc-Si) annealed at different temperatures under air cooling (30 K/s) or slow cooling (0.3 K/s) was investigated by scanning infrared microscopy (SIRM). Comparing to Czochralski-grown silicon (Cz-Si), copper precipitated more easily in mc-Si, and the lowest temperature of copper precipitation in mc-Si was about 700 °C, lower than that in Cz-Si. It was also observed that copper preferably precipitated on grain boundaries so that near the grain boundaries the denuded zone formed. The results indicate that the defects including dislocations, grain boundaries and microdefects, as the heteronucleation sites, enhanced copper precipitation. Moreover, cooling rates had a great influence on the copper precipitation, especially at lower annealing temperatures. Generally air cooling led to the formation of high density of copper-precipitate colonies.