Downward uniformity and optical properties of porous silicon layers

Porous silicon (PS) samples were fabricated by pulse current etching using different times. The downward uniformity and optical properties of the PS layers have been investigated using reflectance spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The relationship between the refractive index and the optical thickness of PS samples and the etching depth has been analyzed in detail. As the etching depth increases, the average refractive index decreases, indicating that the porosity becomes higher, and the formation rate of the optical thickness decreases. Meanwhile, the reflectance spectra exhibit less intense interference oscillations,which mean the uniformity and interface smoothness of the PS layers become worse. In addition, the intensity of PL emission spectra is slightly increased.     

多孔硅薄膜的纵向均匀性及其光学特性研究

多孔硅样品使用脉冲电化学腐蚀法经过不同的腐蚀时间制备完成,使用反射光谱、光致发光光谱和SEM对多孔硅薄膜的纵向均匀性以及其光学特性进行了研究,还详细研究了随腐蚀深度变化的折射率和光学厚度(n*d)等光学参数。实验表明：随着腐蚀深度的增加,多孔硅薄膜的平均折射率n降低,即多孔度变大;多孔硅薄膜的光学厚度的形成速度减小;同时,反射光谱表现更弱的干涉性,表明薄膜的均匀性和界面的平整性变差;另外,光致发光谱的强度微弱变强。     

Temperature: a critical parameter affecting the optical properties of porous silicon

The optical properties of porous silicon (PS) samples fabricated by pulse etching in a temperature rangefrom -40 to 50 ℃ have been investigated using reflectance spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy (SEM). The dependence of the optical parameters, such as the refractive index n and the optical thickness (nd) of PS samples, on the etching temperature has been analyzed in detail. As the etching temperature decreases, n decreases, indicating a higher porosity, and the physical thickness of PS samples also decreases. Meanwhile, the reflectance spectra exhibit a more intense interference band and the interfaces are smoother.In addition, the intensity of the PL emission spectra is dramatically increased.     

温度：影响多孔硅光学特性的一个关键参数

The optical properties of porous silicon（PS） samples fabricated by pulse etching in a temperature range from-40 to 50-C have been investigated using reflectance spectroscopy,photoluminescence spectroscopy,and scanning electron microscopy（SEM）.The dependence of the optical parameters,such as the refractive index n and the optical thickness（nd） of PS samples,on the etching temperature has been analyzed in detail.As the etching temperature decreases,n decreases,indicating a higher porosity,and the physical thickness of PS samples also decreases.Meanwhile,the reflectance spectra exhibit a more intense interference band and the interfaces are smoother.In addition,the intensity of the PL emission spectra is dramatically increased.     

通过脉冲腐蚀形成的多孔硅薄膜的径向微结构和光学特性研究

使用反射光谱、光致发光光谱和SEM研究了通过脉冲腐蚀形成的多孔硅薄膜的径向折射率、光学和物理厚度。详细分析了沿径向方向多孔硅薄膜的径向折射率(n)和光学厚度(nd)与腐蚀中心之间的关系。实验结果表明：随着远离腐蚀中心,SEM图像表明：多孔硅样品的物理厚度缓慢变小,在腐蚀边缘,在径向58μm距离里,薄膜的物理厚度从2.48μm减少到1.72μm;此外,径向折射率n增加,即多孔度变小,同时,反射光谱强度显示出干涉振荡减弱,这意味着多孔硅薄膜的均匀性和界面的平整度变坏。光致发光谱的包络线显示蓝移的趋势,显示纳米微粒的尺寸减少。多孔硅微腔被制备用来研究多孔硅膜的径向光学特性,结果证实：在腐蚀中心,多孔硅膜的均匀性比边缘好。     

Influence of etching current density on the morphology of macroporous silicon arrays by photo-electrochemical etching

Macroporous silicon arrays(MSA) have attracted much attention for their potential applications in photonic crystals,silicon microchannel plates,MEMS devices and so on.In order to fabricate perfect MSA structure,photo-electrochemical (PEC) etching of MSA and the influence of etching current on the pore morphology were studied in detail.The current-voltage curve of a polished n-type silicon wafer was presented in aqueous HF using back-side illumination.The critical current density J_(PS) was discussed and ...     

电流密度对光电化学腐蚀宏孔硅阵列形貌的影响

宏孔硅阵列(MSA)在光子晶体、硅微通道板、MEMS 器件等领域应用前景广阔,引起人们广泛关注。为制备理想的MSA结构,本文开展了MSA光电化学方法腐蚀实验,重点研究了腐蚀电流密度对宏孔形貌的影响。给出了n型硅抛光片背面光照情况下在氢氟酸溶液中的电流-电压扫描曲线,讨论了临界电流密度JPS的意义和MSA稳定生长的基本电流密度条件。提出了一种间接地测量JPS与腐蚀时间关系的方法,并根据JPS的测量结果调整腐蚀电流,实现了理想的MSA等径生长,制备出孔深度为295m,长径比为98的MSA结构。     

Radial microstructure and optical properties of a porous silicon layer by pulse anodic etching

This paper investigates the radial refractive index and optical and physical thicknesses of porous silicon (PS) layers prepared by pulse etching by means of reflectance spectroscopy,photoluminescence spectroscopy and scanning electron microscopy(SEM).The relationship between the radial refractive index and optical thickness of the PS sample and the position away from the etched centre along the radial direction has been analyzed in detail. With the position farther away from the etched centre,the SEM image shows that the physical thickness of the PS sample decreases slowly,whereas intensely decreases from 2.48 to 1.72μm near the edge at a distance of 58μm.Moreover,the radial refractive index increases,indicating that the porosity becomes smaller.Meanwhile,the reflectance spectra exhibit the less intense interference oscillations,which mean that the uniformity and interface smoothness of the PS layers become worse,and the envelope curves of photoluminescence spectra exhibit a trend of blue-shift,indicating a reduction in nanocrystal dimensions.The PS micro-cavity is prepared to study the radial optical properties of the PS layer,and the results verify that the uniformity and smoothness of the PS layer in the centre are better than those at the edge.     

Effect of the interface states on the cell parameters of a thin film quasi-monocrystalline porous silicon as an active layer

Unlike crystalline silicon, quasi-monocrystalline porous silicon (QMPS) layers have a top surface with small voids in the body. What is more pertinent to the present study is the fact that, at a given wavelength of interest for solar cells, these layers are often reported, in the literature, to have a higher absorption coefficient than crystalline silicon. The present study builds on existing literature, suggesting an analytical model that simulates the performance of an elementary thin QMPS (as an active layer) solar cell. Accordingly, the effects that the interface states located at the void-silicon interface and that the porosity of this material have on the cell parameters are investigated. Furthermore, the effects of the optimum base doping, QMPS thickness, and porosity on the photovoltaic parameters were taken into consideration. The results show that the optimum base doping depends on the QMPS thickness and porosity. For an 8 μm thickness, the film QMPS layer gives a 35.4 mA/cm² for short-circuit current density, 15% for conversion efficiency, and 527 mV for open-circuit voltage when the value of the interface states is about 10¹² cm⁻² and the base doping is about 2×10¹⁸ cm⁻³ under AM 1.5 conditions.     

Optical and electrical properties of porous silicon layer formed on the textured surface by electrochemical etching

Porous silicon (PS) layers were formed on textured crystalline silicon by electrochemical etching in HF-based electrolyte. Optical and electrical properties of the TMAH textured surfaces with PS formation are studied. Moreover, the influences of the initial structures and the anodizing time on the optical and electrical properties of the surfaces after PS formation are investigated. The results show that the TMAH textured surfaces with PS formation present a dramatic decrease of reflectance. The longer is the anodizing time, the lower is the reflectance. Moreover, an initial surface with bigger pyramids achieved lower reflectance in short wavelength range. A minimum reflectance of 3.86 % at 460 nm is achieved for a short anodizing time of 2 min. Furthermore, the reflectance spectrum of the sample, which was etched in 3 vol.% TMAH for 25 min and then anodized for 20 min, is extremely flat and lies between 3.67% and 6.15% in the wavelength range from 400 to 1040 nm. In addition, for a short anodizing time, a slight increase in the effective carrier lifetime is observed. Our results indicate that PS layers formed on a TMAH textured surface for a short anodization treatment can be used as both broadband antireflection coatings and passivation layers for the application in solar cells.     

Structural,electronic and optical properties of Ilmenite ATiO3(A=Fe,Co, Ni)

Ilmenite-type ATiO₃ (A=Fe, Co, Ni) crystals have been investigated via Generalized Gradient Approximation (GGA) in the scheme of Revised Perdew-Burke-Ernzerhof (RPBE) using the first-principles method. The band structures, densities of states, bond orders and charge populations, optical properties including the dielectric function ε(ω), absorption coefficient I(ω), refractive index n(ω), extinction coefficient k(ω), electron energy loss function L(ω) and reflectivity function R(ω), are calculated. The results show that the GGA-optimized geometries agree well with the experimental data. FeTiO₃ has a direct band gap, but both CoTiO₃ and NiTiO₃ exhibit indirect band gap. The analysis for densities of states and atomic charge populations exhibits that TiO bonds possess the stronger covalent bonding strength than AO bonds. The calculated optical properties along [100], [010] and [001] as well as polycrystalline directions demonstrate the significant optical anisotropy parallel and perpendicular to c-axis for ATiO₃. Finally, the origins of main peaks for optical spectra are presented based on electron transitions. Theoretical insights into the microscopic intrinsic properties of ATiO₃ should provide fundamental investigations for further understanding the Ilmenite ATiO₃ materials and improving their practical applications.     

Ar^＋注入多孔硅与Ar^＋注入硅多孔结构的光致发光研究

研究了中等能量(30 key)Ar+注入多孔硅和中等能量(30 key)Ar+先注入单晶硅后再进行电化学腐蚀成的多孔结构的光致发光特性.研究结果表明:中等能量(30 key)Ar+注入多孔硅后,多孔硅原有的发光峰消失,主要是Ar+对多孔硅表面氧的剥离作用.使得与氧相关发光的结构消失,多孔硅不再发光;中等能量(30 kev)Ar+先注入单晶硅后冉电化学腐蚀成的多孔结构中,通常多孔硅原有的580 nIn附近发光峰强度随注入Ar+剂量的增加而增强,并有红移;同时在谱峰处于470 nm附近的微弱发光峰不因注入Ar+而明显变化.     

Optical and electrical properties of porous silicon layer formed on the textured surface by electrochemical etching

Porous silicon(PS) layers were formed on textured crystalline silicon by electrochemical etching in HF-based electrolyte.Optical and electrical properties of the TMAH textured surfaces with PS formation are studied. Moreover,the influences of the initial structures and the anodizing time on the optical and electrical properties of the surfaces after PS formation are investigated.The results show that the TMAH textured surfaces with PS formation present a dramatic decrease in reflectance.The longer the anodizing time is,the lower the reflectance.Moreover,an initial surface with bigger pyramids achieved lower reflectance in a short wavelength range.A minimum reflectance of 3.86%at 460 nm is achieved for a short anodizing time of 2 min.Furthermore,the reflectance spectrum of the sample,which was etched in 3 vol.%TMAH for 25 min and then anodized for 20 min,is extremely flat and lies between 3.67%and 6.15%in the wavelength range from 400 to 1040 nm.In addition,for a short anodizing time,a slight increase in the effective carrier lifetime is observed.Our results indicate that PS layers formed on a TMAH textured surface for a short anodization treatment can be used as both broadband antireflection coatings and passivation layers for the application in solar cells.     

First-principles study of the electronic structures and optical properties of C--F--Be doped wurtzite ZnO

The electronic structure and optical properties of pure, C-doped, C-F codoped and C-F-Be cluster-doped ZnO with wurtzite structure were calculated by density functional theory with the plane-wave ultrasoft pseudopotentials method. The results indicate that p-type ZnO can be obtained by C incorporation, and the energy level of CO above valence band maximum is 0.36 eV. The ionization energy of the complex Zn16O14CF and Zn15BeO14CF can be reduced to 0.23 and 0.21 eV, individually. These results suggest that the defect complex of Zn15BeO14CF is a better candidate for p-type ZnO. To make optical properties clear, we investigated the imaginary part of the complex dielectric function of undoped and C-F-Be doped ZnO. We found that there are strong absorption in the energy region less than 2.7 eV for C-F-Be doped system comparing to pure ZnO.     

Effect of Ag photo-doping on structural,optical and phase change properties of GeTe chalcogenide films

This paper reports the effect of Ag photo-doping on optical, electrical and structural properties of GeTe:Ag thin films. The absence of sharp diffraction peak confirms the amorphous nature of as-deposited and photo-doped films. The decrease in reflectance of GeTe:Ag bilayer films with photo-doping reaction time has been observed. The RAMAN spectrum showed the characteristic Raman bands for GeTe₄ (127 cm⁻¹), long chain interactions of Te–Te chains (145 cm⁻¹) and a broad peak for Ge–Ge vibrations (275 cm⁻¹) without appreciable change in their position/shape with photodoped Ag concentration. The electrical resistivity measurement shows that photo-doping of Ag led to sharp amorphous-crystalline phase transition along with an increase in transition temperature and resistivity value in both amorphous as well as crystalline state. The annealing of photo-doped GeTe:Ag samples showed an enhancement in the crystallinity of GeTe phase without any segregation of Ag phases in annealed samples. The preferential formation of GeTe (200) phase upon crystallization has been observed for GeTe:Ag films. Different optical parameters have been calculated for photo-doped and annealed samples and are discussed in conjunction with the modification of network structure of GeTe with inclusion of photo-doped Ag content.     

Structural and optical properties of silicon nanowires synthesized by Ag-assisted chemical etching

Metal-assisted chemical etching (MACE) of silicon in an aqueous solution of hydrofluoric acid and hydrogen peroxide is established for the fabrication of large-area uniform silicon nanowire (SiNW) arrays. The effect of the silver catalyst layer thickness on the morphology of the synthesized nanostructures and nanowires is investigated. Atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM) reveal that the morphology of the fabricated silicon nanostructures remarkably depends on the catalyst layer thickness, and an optimum layer thickness is necessary for the fabrication of SiNWs. Also the effect of different etching times on the structural and optical properties of the fabricated SiNWs is investigated. FESEM showed a linear increment of the nanowire length and slight diameter changes through different etching times. The ultralow reflectance of SiNWs in the absorption region through the measurement of specular and diffuse reflectance showed that with increase in the etching time, the total reflectance remarkably decreases. A broadband visible photoluminescence (PL) emission from these wires was observed, and it could be stated that the silicon nanocrystals (SiNCs) are mostly responsible for the PL emission. The SiNC sizes were determined by an analytical model through a frequency shift in the Raman spectrum. The synthesized optically-active SiNWs could, therefore, be considered as a promising candidate for a new generation of nanoscale opto-electronic devices.     

Impact of substrate temperature on the structural,optical and electrical properties of thermally evaporated SnS thin films

Tin Sulfide thin films were deposited on soda lime glass substrates at three different substrate temperatures using thermal evaporation technique. The impact of substrate temperature on the deposited films has been studied thoroughly. Surface morphology was modified with the substrate temperature. XRD spectra shows orthorhombic end-centered type SnS having (1 1 0) orientation. The crystallite size increases with the increase in the substrate temperature. At a high substrate temperature (450 °C) small grains form on the surface and crystallinity decreases. The effect of substrate temperature on optical and electrical properties has been studied using UV–Vis–NIR Spectrophotometer and Hall effect respectively. With the increase in the substrate temperature there is a substantial decrease in the transmittance and bandgap value. Refractive index (n), dielectric constant (ε₁) and extinction co-efficient (k) have also been calculated for different substrate temperatures.     

石墨衬底多晶硅籽晶层制备及性质

采用磁控溅射技术在石墨衬底上制备多晶硅籽晶层,系统研究了不同衬底温度、不同快速热退火(RTA)温度和时间对籽晶层结构性质的影响。通过X射线衍射(XRD)仪测试分析,发现溅射过程中衬底温度对于结晶质量有着至关重要的影响,即衬底温度为700℃是形成Si(220)晶面择优取向的临界温度,当衬底温度高于700℃时,Si(220)晶面衍射峰峰高随衬底温度的增加显著增大。在RTA过程中,提高退火温度和延长退火时间均能够提高薄膜多晶硅籽晶层Si(220)晶面的择优取向。     

Structural,optical dispersion and dielectric properties of novel chromium nickel organic crystalline semiconductors

A novel organic crystalline semiconductor, [Cr(DPPP)(DPPM)(Ni-ap)(CO)₂] (Cr–Ni OSC) (6a), (DPPP=diphenylphosphino-propanone, DPPM=diphenylphosphino-methane and Ni-ap=nickel apyrazole ring) (6a) was synthesized. Structural characteristics of the Cr–Ni OSC complex have been investigated by IR, ¹HNMR, ³¹P NMR, thermal analysis (TG/DTA), and XRD. Thermal analysis of Cr–Ni OSC implies that, the complex was thermally stable up to 218 °C, and the melting point of it was 193 °C. Two discrete regions of (44.46%, 128–421 °C) and (41.15%, 600–823 °C) by TG analysis of Cr–Ni OSC complex was determined. XRD crystal data of Cr–Ni OSC showed the formation of monoclinic (P2₁/n). Transmittance and reflectance have been used to determine the optical dispersion and dielectric properties of the Cr–Ni OSC complex in the range of 200–800 nm. The transparency of the complex is 75–80% in the visible range. The optical and transport energy gaps were estimated as 1.87 eV and 2.01 eV respectively. Optical dispersion parameters have been calculated by using single term Sellmeier dispersion relation and Wemple–DiDomenico single oscillator model. Several dispersion parameters were determined by analysis of refractive index dispersion. The optical conductivity, surface and volume energy loss functions, and the electric modulus were also estimated from the optical dielectric constant analysis.     

氧等离子环境下影响多孔硅光学特性的因素

研究了多孔硅（porous silicon,PS） 在氧等离子体环境中退火温度和存储时间对PS光学稳定性的影响。通过光致发光（PL） 谱和傅里叶变换红外光谱对系列样品进行分析。高斯拟合结果显示PL谱由三个高斯峰叠加而成,其中至少两个高斯峰是由非量子限制效应造成的,即第一峰面积的变化与Si=O双键密切相关,第三峰面积的变化与Si-O-Si桥键以及SiHx（x=1,2）键有关;退火温度对以上两个峰的强弱变化有直接影响。