半导体二次电子像中的掺杂衬度

本文详细评述和介绍了近几年来国际上关于扫描电镜二次电子像中的掺杂衬度方面的实验和理论研究成果 ,总结了实验中发现的各种现象 ,并用电离能的观点对所有这些现象作出了理论上的解释 。

Mg-doped SrTaO_(2)N as a visible-light-driven H_(2)-evolution photocatalyst for accelerated Z-scheme overall water splitting

Perovskite SrTaO_(2)N is one of the most promising narrow-bandgap photocatalysts for Z-scheme overall water splitting.However,the formation of defect states during thermal nitridation severely hinders the separation of charges,resulting in poor photocatalytic activity.In the present study,we successfully synthesize SrTaO_(2)N photocatalyst with low density of defect states,uniform morphology and particle size by flux-assisted one-pot nitridation combined with Mg doping.Some important parameters,such as the size of unit cell,the content of nitrogen,and microstructure,prove the successful doping of Mg.The defect-related carrier recombination has been significantly reduced by Mg doping,which effectively promotes the charge separation.Moreover,Mg doping induces a change of the band edge,which makes proton reduction have a stronger driving force.After modifying with the core/shell-structured Pt/Cr_(2)O_(3)cocatalyst,the H_(2)evolution activity of the optimized SrTaO_(2)N:Mg is 10 times that of the undoped SrTaO_(2)N,with an impressive apparent quantum yield of 1.51%at 420 nm.By coupling with Au-FeCoO_(x)modified BiVO_(4)as an O_(2)-evolution photocatalyst and[Fe(CN)_(6)]_(3)−/[Fe(CN)_(6)]_(4)−as the redox couple,a redox-based Z-scheme overall water splitting system is successfully constructed with an apparent quantum yield of 1.36%at 420 nm.This work provides an alternative way to prepare oxynitride semiconductors with reduced defects to promote the conversion of solar energy.

S掺杂ZnO纳米棒的水热法制备及其性能研究

本文利用低温二步水热法在ITO玻璃衬底上制备了ZnO以及S掺杂的ZnO纳米棒，研究和比较了ZnO纳米棒和不同含量S掺杂的ZnO纳米棒的形貌和光学等特性。研究发现低浓度硫脲掺杂时，纳米棒均匀性好，且具有良好的晶体结构和C轴生长取向，相对于未掺杂的ZnO纳米棒在蓝光波段出现较强的发光峰。高浓度硫脲掺杂时，纳米结构出现相结构和表面形貌的分离，并且不同的区域具有不同的导电性。CL谱也显示出在蓝光波段较强的发光峰，预示着通过硫的掺杂可以扩展ZnO在蓝光发光波段的光电器件领域的应用。

基于扫描电子显微镜的半导体掺杂剂含量剖面分析研究进展

掺杂剂浓度剖面分析是半导体器件研发、诊断和电学性能提升的关键。扫描电子显微镜因具有埃级空间分辨率、成像速度快、荷电效应弱和辐照损伤小等优点,在表征掺杂半导体方面独具优势。本文简要介绍了扫描电子显微镜在掺杂半导体表征方面的研究进展及挑战,包括SEM图像中掺杂衬度的产生机理、成像参数以及SE的能量和出射角度对掺杂衬度的影响、不同掺杂类型半导体的成像研究进展等。

Schiff碱基过渡金属镍络合物的电化学聚合：阳极电聚合中扫描速率的影响(英文)

采用线性电位扫描法制备了水杨醛-Schiff碱基过渡金属镍络合物的聚合物poly[Ni(salen)],扫描速率为5-150 mV.s-1.采用场发射显微镜观察了聚合物poly[Ni(salen)]的表面形貌.研究了电聚合中扫描速率对聚合物生长的影响,电聚合速率(dГ/dm)与扫描速率(v)呈指数衰退关系,通过库仑电量分析指出电聚合扫描速率在20mV.s-1时聚合产物中含有最多的氧化还原活性点.扫描速率提高时单体的扩散步骤限制了聚合物的生长,所以氧化还原活性点总量随着扫描速率的提高而开始下降.利用循环伏安法分析了聚合物poly[Ni(salen)]的扩散动力学,结果表明在20 mV.s-1时制备的聚合物具有较大的电荷扩散系数.

Crystal Structure and Photocatalytic Characteristics of Nanoscate Sb-doped TiO_2 Thin Films

Nanoscale Sb doped titanium dioxide thin films photocatalyst （Ti1-xSbO2） were obtained from dip-coating sol-gel method. The influence of dopant Sb density on the crystal structure and the phase transformation of the thin tilms were characterized by X-ray diffraction （XRD） and Raman spectra. The results of XRD showed that as prepared lilms were not only in anatase state but also in brookite. The crystalline size was estimated to be around 13.3-20 nm. Raman spectra indicated there coexisted other phases and a transformation from brookite to anatase in the samples doped with 0.2% Sb. After doping a proper amount of Sb, the cryst,allization rate and the content of the anatase Ti1-x, SbO2 in the thin films was clearly enhanced because Sb replaced part. of the Ti of TiO2 in the thin films. The anode current density （photocurrent density） and the first order reaction speed constant （k） of t.hin films doped with 0.2% Sb reached 42.49 μA/cm^2 and 0.171 h/cm^2 under 254 nm UV illumination, respectively, which is about 11 times and 2 times that of the non doped TiO2 anode prepared by the same method respectively.

Growth and Optical Properties of ZnO Films and Quantum Wells

The growth characteristics during metalorganic chemical vapor deposition and optical properties of ZnO films on sapphire （Al2O3） （0001） and （1120） substrates are studied. For the former,the effects of two important growth parameters,i, e. temperature and pressure, are investigated in detail. Due to the large lattice mismatch between the film and the substrate, ZnO nanocrystals are usually obtained. The growth behavior at the film-substrate interface is found to be strongly dependent on the growth temperature,while the growth pressure determines the shape of the nanostructures as they grow. It is difficult to obtain ZnO films that have good quality and a smooth surface simultaneously. Due to the smaller lattice mismatch,the critical thickness of ZnO on the Al2O3 （1120） surface is found to be much larger than that on the Al2O3 （0001） surface. ZnO/MgZnO quantum wells with graded well thicknesses are grown on the Al2O3 （1120） surfaces,and their optical properties are studied. The built-in electric field in the well layer, generated by the piezoelectric effect, is estimated to be 3 × 10^5 V/cm. It is found that growth at low temperatures and low pressures may facilitate the incorporation of acceptor impurities in ZnO.

两种改性方法对磁性纳米TiO_2光催化性能的影响

采用溶胶-凝胶法制备了Fe_3O_4@SiO_2@TiO_2和Fe^(3+)掺杂Fe_3O_4@SiO_2@TiO_2两种复合光催化剂.以降解甲基对硫磷溶液为反应模型,研究了煅烧温度、煅烧时间、TiO_2层厚度和Fe^(3+)掺杂度对TiO_2光催化性能的影响.通过扫描电镜(SEM)、傅立叶变换红外光谱仪(IR)、X-射线衍射仪(XRD)和固体紫外可见漫反射(UV-Vis)等分析手段对复合光催化剂进行表征.结果表明:Fe_3O_4@SiO_2@TiO_2在450℃煅烧3.5 h时光催化性能最好,其钛酸四丁酯和Fe_3O_4@SiO_2的最佳用量为9 mL:2 g(v:m).Fe^(3+)掺杂Fe_3O_4@SiO_2@TiO_2在450℃煅烧4.0 h时光催化性能最好,Fe^(3+)最佳掺杂度为0.35 mol%,钛酸四丁酯和Fe_3O_4@SiO_2的最佳用量为9 m L:0.5 g(v:m).两种复合型TiO_2光催化剂均为锐钛型,且都能使TiO_2的吸收光区红移,但Fe_3O_4@SiO_2@TiO_2红移更明显,光催化效果更好.

Equivalent Doping Transformation Method for Predicting Breakdown Voltage and Peak Field at Breakdown of Epitaxial-Diffused Punch-Through Junction

Based on a new semi empirical analytical method, namely equivalent doping transformation, the breakdown voltage and the peak field of the epitaxial diffused punch through junction have been obtained. The basic principle of this method is introduced and a set of breakdown voltage and peak field plots are provided for the optimum design of the low voltage power devices. It shows that the analytical results coincide with the previous numerical simulation well.

An Improved Description of Characteristics Length in Substrate Current Model for Submicron and Deep-Submicron LDD MOSFET's

A novel substrate current model is proposed for submicron and deep-submicron li ghtly-doped-drain (LDD) n-MOSFET,with the emphasis on accurate description of the characteristics length by taking the effects of channel length and bias int o account.This is due to that the characteristics lenth significantly affects th e maximum lateral electric field and the length of velocity saturation region,bo th of which are very important in modeling the drain current and the substrate c urrent.The comparison between simulations and experiments shows a good predictio n of the model for submicron and deep-submicron LDD MOSFET.Moreover,the analyti cal model is suitable for descgn of devices as it is low in computation consumpt ion.

Optimization and Analysis of Magnesium Doping in MOCVD Grown p-GaN

p-type conductivity and crystal quality of Mg-doped GaN grown by MOCVD have been improved through opti- mization of the magnesium flow rate. The hole concentration first increased and then decreased with the magnesium flow rate while the mobility decreased monotonously. The optimum sample reached a hole concentration of 4. 1×10^17cm -3 and a resistivity of 1Ω·cm. Based on a self-compensation model involving the deep donor Mo, VN, we calculate the hole con- centration as a function of magnesium doping concentration NA ,which indicates that the self-compensation coefficient in- creases with NA;the hole concentration first increases with NA and reaches a maximum at NA≈4×10^19 ,then decreases rapidly as doping concentration increases. XRD also indicate that dislocation density decreased as magnesium flow rate decreased.

Device Characteristics Comparison Between GaAs Single and Double Delta-Doped Pseudomorphic High Electron Mobility Transistors

The Al 0.24Ga 0.76As/In 0.22Ga 0.78As single delta-doped PHEMT (SH-PHEMT) and double delta-doped PHEMT (DH-PHEMT) are fabricated and investigated.Based on the employment of double heterojunction,double delta doped design,the DH-PHEMT can enhance the carrier confinement,increase the electron gas density,and improve the electron gas distribution,which is beneficial to the device performance.A high device linearity,high transconductance over a large gate voltage swing,high current drivability are found in DH-PHEMT.These improvements suggest that DH-PHEMT is more suitable for high linearity applications in microwave power device.

Band structures of TiO_2 doped with N, C and B

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)- and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of im-purity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of im-purity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Electronic Structure and Magnetic Properties of Cr-Doped AlN

To understand the electronic and magnetic properties, we have studied Cr-doped zinc-blende AlN system in detail by applying a first-principle plane wave pseudopotential method based on the density functional theory within the local spin density approximation. The analyses of the band structures, density of states, exchange interactions, and magnetic moments show that Al1-xCrxN alloys may exhibit a half-metallic ferromagnetism character, that Cr in the diluted doping limit forms near-midgap deep levels, and that the total magnetization of the cell is 3μB per Cr atom, which does not change with Cr concentration. Moreover, we have succeeded in predicting that Al1-xCrzN alloys in x = 0.0625 has a very high Curie temperature, and lind that ferromagnetic exchange interaction between magnetic dopants is short-ranged.

Defects Energetics and Electronic Properties of Li Doped ZnO： A Hybrid Hartree-Fock and Density Functional Study

The electronic properties and stability of Li-doped ZnO with various defects have been stud- ied by calculating the electronic structures and defect formation energies via first-principles calculations using hybrid Hartree-Fock and density functional methods. The results from formation energy calculations show that Li pair complexes have the lowest formation energy in most circumstances and they consume most of the Li content in Li doped ZnO, which make the p-type conductance hard to obtain. The formation of Li pair complexes is the main obstacle to realize p-type conductance in Li doped ZnO. However, the formation energy of Lizn decreases as environment changes from Zn-rich to O-rich and becomes more stable than that of Li-pair complexes at highly O-rich environment. Therefore, p-type conductance can be obtained by Li doped ZnO grown or post annealed in oxygen rich atmosphere.

Effects of heat treatment conditions and Y-doping on structure and phase transition temperature of VO2 powders

The VO2 powders were prepared by hydrothermal synthesis.The effects of heat treatment conditions and Y-doping on the structure and phase transition temperature of VO2 were studied.The XRD,SEM and TEM results show that the heat treatment temperature has a significant effect on the crystal transformation of VO2 precursor.Increasing temperature is conducive to the transformation of precursor VO2(B)to ultrafine VO2(M).The Y-doping affects the structure of VO2.Y^3+can occupy the lattice position of V4+to form YVO4 solid solution,which can increase the cell parameters of VO2.Due to the lattice deformation caused by Y-doping,the aggregation of particles is prevented,and the grain is refined obviously.DSC curves show that Y-doping can reduce the phase transition temperature of VO2(M).After adding 9 at.%Y,the phase transition temperature can be reduced from 68.3 to 61.3℃.

Crystallization Behavior and Properties of B-Doped ZnO Thin Films Prepared by Sol-Gel Method with Different Pyrolysis Temperatures

Boron-doped zinc oxide transparent （BZO） films were prepared by sol-gel method. The effect of pyrolysis temperature on the crystallization behavior and properties was systematically investigated. XRD patterns revealed that the BZO films had wurtzite structure with a preferential growth orientation along the c-axis. With the increase of pyrolysis temperature, the particle size and surface roughness of the BZO films increased, suggesting that pyrolysis temperature is the critical factor for determining the crystallization behavior of the BZO films. Moreover, the carrier concentration and the carrier mobility increased with increasing the pyrolysis temperature, and the mean transmittance for every film is over 90% in the visible range.

Unusual Charge Transport and Spin Response of Doped Bilayer Triangular Antiferromagnets

Within the t-J model, the charge transport and spin response of the doped bilayer triangular antiferromagnetare studied by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in theelectronic structure, the qualitative behaviors of the physical properties are the same as in the single layer case. Theconductivity spectrum shows the low-energy peak and unusual midinfrared band, the temperature-dependent resistivityis characterized by the nonlinearity metallic-like behavior in the higher temperature range and the deviation from themetallic-like behavior in the lower temperature range and the commensurate neutron scattering peak near the half-fillingis split into six incommensurate peaks in the underdoped regime, with the incommensurability increasing with the holeconcentration at lower dopings, and saturating at higher dopings.

Effect of deposition temperature on properties of boron-doped diamond films on tungsten carbide substrate

Boron-doped diamond(BDD)films were deposited on the tungsten carbide substrates at different substrate temperatures ranging from 450 to 850°C by hot filament chemical vapor deposition(HFCVD)method.The effect of deposition temperature on the properties of the boron-doped diamond films on tungsten carbide substrate was investigated.It is found that boron doping obviously enhances the growth rate of diamond films.A relatively high growth rate of 544 nm/h was obtained for the BDD film deposited on the tungsten carbide at 650°C.The added boron-containing precursor gas apparently reduced activation energy of film growth to be 53.1 kJ/mol,thus accelerated the rate of deposition chemical reaction.Moreover,Raman and XRD analysis showed that heavy boron doping(750 and 850°C)deteriorated the diamond crystallinity and produced a high defect density in the BDD films.Overall,600-700°C is found to be an optimum substrate temperature range for depositing BDD films on tungsten carbide substrate.

An analytical model to explore open-circuit voltage of a-Si:H/c-Si heterojunction solar cells

The effect of the parameters on the open-circuit voltage, V_(OC) of a-Si:H/c-Si heterojunction solar cells was explored by an analytical model. The analytical results show that V_(OC) increases linearly with the logarithm of illumination intensity under usual illumination. There are two critical values of the interface state density(D_(it)) for the open-circuit voltage(V_(OC)), D_(it)^(crit,1) and D_(it)crit,2(a few 1010 cm^(-2)·e V^(-1)). V_(OC) decreases remarkably when D_(it) is higher than D_(it)^(crit,1). To achieve high V_(OC), the interface states should reduce down to a few 1010 cm^(-2)·e V^(-1). Due to the difference between the effective density of states in the conduction and valence band edges of c-Si, the open-circuit voltage of a-Si:H/c-Si heterojunction cells fabricated on n-type c-Si wafers is about 22 mV higher than that fabricated on p-type c-Si wafers at the same case. V_(OC) decreases with decreasing the a-Si:H doping concentration at low doping level since the electric field over the c-Si depletion region is reduced at low doping level. Therefore, the a-Si:H layer should be doped higher than a critical value of 5×10^(18) cm^(-3) to achieve high V_(OC).