Visible and infrared photoluminescence from Er-doped SiOx

The annealing behaviors of photoluminescence of SiO_x and Er-doped SiO_x grown by molecular beam epitaxy in the wavelength range of visible and infrared light are studied. For SiO_x, four PL bands located at 510, 600, 716 and 810 nm, respectively, are observed. For Er-doped SiO_x, the 716 nm band, which is believed to be originated from the electron–hole recombination at the interface between crystalline Si and amorphous SiO₂, disappears in the annealing temperature range of 500–900°C. It is suggested the enhancement of Er luminescence is partially due to the energy transfer from the recombination at the interface between crystalline Si and SiO₂ to Er ions.     

Crystalline silicon surface passivation investigated by thermal atomic-layer-deposited aluminum oxide

Atomic-layer-deposited(ALD) aluminum oxide(Al_2O_3) has demonstrated an excellent surface passivation for crystalline silicon(c-Si) surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-based thermal atomic layer deposition of Al_2O_3 films are fabricated for c-Si surface passivation. The influence of deposition conditions on the passivation quality is investigated. The results show that the excellent passivation on n-type c-Si can be achieved at a low thermal budget of 250℃ given a gas pressure of 0.15 Torr. The thickness-dependence of surface passivation indicates that the effective minority carrier lifetime increases drastically when the thickness of Al_2O_3 is larger than 10 nm. The influence of thermal post annealing treatments is also studied. Comparable carrier lifetime is achieved when Al_2O_3 sample is annealed for 15 min in forming gas in a temperature range from 400℃ to 450℃. In addition, the passivation quality can be further improved when a thin PECVD-SiN_x cap layer is prepared on Al_2O_3, and an effective minority carrier lifetime of2.8 ms and implied Voc of 721 mV are obtained. In addition, several novel methods are proposed to restrain blistering.     

后退火增强氢化非晶硅钝化效果的研究

在本征氢化非晶硅(a-Si:H(i))/晶体硅(c-Si)/a-Si:H(i)异质结构上溅射ITO时, 发现后退火可大幅增加ITO/a-Si:H(i)/c-Si/a-Si:H(i)的少子寿命(从1.7 ms到4 ms). 这一增强效应可能的三个原因是: ITO/a-Si:H(i)界面场效应作用、退火形成的表面反应层影响以及退火对a-Si:H(i)材料本身的优化, 但本文研究结果表明少子寿命增强效应与ITO和表面反应层无关; 对不同沉积温度制备的a-Si:H(i)/c-Si/a-Si:H(i)异质结后退火的研究表明: 较低的沉积温度(<175 ℃)后退火增强效应显著, 而较高的沉积温度(>200 ℃)后退火增强效应不明显, 可以确定“低温长高温后退火”是获得高质量钝化效果的一种有效方式; 采用傅里叶红外吸收谱(FTIR)研究不同沉积温度退火前后a-Si:H(i)材料本身的化学键构造, 发现退火后异质结少子寿命大幅提升是由于a-Si:H(i)材料本身的结构优化造成的, 其深层次的本质是通过材料的生长温度和退火温度的优化匹配来控制包括H含量、H键合情况以及Si原子无序性程度等微观因素主导作用的一种竞争性平衡, 对这一平衡点的最佳控制是少子寿命大幅提升的本质原因.     

UHV-MOCVD growth of TiO2 on SiOx/Si(1 1 1): Interfacial properties reflected in the Si 2p photoemission spectra

Metal–organic chemical vapour deposition growth of titanium oxide on moderately pre-oxidised Si(1 1 1) using the titanium(IV) isopropoxide precursor has been studied for two different growth modes, reaction-limited growth at 300 °C and flux-limited growth at 500 °C. The interfacial properties have been characterized by monitoring synchrotron radiation excited Si 2p photoemission spectra. The cross-linking from oxidised Si to bulk Si after TTIP exposure has been found to be very similar to that of SiO_x/Si(1 1 1). However, the results show that the additional oxidation of Si most probably causes a corrugation of the SiO_x/Si interface. Those conclusions are valid for both growth modes. A model is introduced in which the amorphous interface region is described as (TiO₂)_x(SiO₂)_y where x and y changes linearly and continuously over the interface. The model quantifies how (TiO₂)_x(SiO₂)_y mixing changes the relative intensities of the signals from silicon oxide and silicon. The method can be generalised and used for the analyses of other metal-oxides on silicon.     

掺杂非晶氧化硅薄膜中三元化合态与电子结构的第一性原理计算

基于密度泛函理论和分子动力学方法,研究了ITO-SiO_x(In,Sn)/n-Si异质结光伏器件中非晶SiO_x层的氧化态和电子结构.计算结果表明:具有钝化隧穿功能的超薄(2 nm)非晶SiO_x层,是由In,Sn,O,Si四种元素相互扩散形成的,其中In,Sn元素在SiO_x网格中以In-O-Si和Sn-O-Si成键态存在,形成了三元化合物.In和Sn的掺杂不仅在SiO_x的带隙中分别引入了E_v+4.60 eV和E_v+4.0 eV两个电子能级,还产生了与In离子相关的浅掺杂受主能级(E_v+0.3 eV).这些量子态一方面使SiO_x的性能得到改善,在n-Si表面形成与反型层相衔接的p-型宽禁带"准半导体",减少了载流子的复合,促进了内建电场的建立.另一方面有效地降低了异质结势垒高度,增强了ITO-SiO_x(In,Sn)/n-Si光伏器件中光生非平衡载流子的传输概率,促进了填充因子的提升(72%).     

SiO_x(x=1.3)薄膜的优化阻变特性与退火温度的关系探究

采用电子束蒸发技术在Si衬底上制备了亚氧化硅SiOx(x=1.3)薄膜,研究了不同温度热退火处理的SiOx薄膜作为阻变层的ITO/SiOx/Si/Al结构的阻变特性.研究发现,在电极尺寸相同的条件下,随着退火温度的增加,该结构的高低阻态比显著提高,最高可达109.X射线光电子能谱和电子顺磁共振能谱的分析表明,不同退火温度下形成的不同价态的硅悬挂键是低阻态下细丝通道的主要来源.椭偏仪的测试结果表明,经过热退火处理的SiOx薄膜折射率的增大是导致高阻态下器件电阻增大的原因.     

Strong visible photoluminescence in amorphous SiOx and SiOx : H thin films prepared by thermal evaporation of SiO powder

Amorphous SiO_x and SiO_x : H films were prepared by thermal evaporation of SiO powder in ultrahigh vacuum or under a flow of hydrogen ions onto silicon substrates maintained at 100°C. Photoluminescence (PL) can be seen in the visible range with the naked eye on the as-deposited samples without post-treatments. Composition and structure investigations were performed by infrared and Raman spectrometry experiments on films annealed at different temperatures. Hydrogen and oxygen bonding was studied by infrared spectrometry. The PL is attributed to the quantum confinement of excitons in a-Si clusters embedded in the a-SiO_x matrix. Our results demonstrate that oxygen creates an efficient potential barrier and no further passivation by hydrogen is necessary.     

准周期层状铁磁超晶格的实空间重整化群方法

本文用实空间重整化群方法讨论了准周期层状铁磁超晶格的磁自旋波,用Reduce语言推导了decimation变换公式,从而求得了局域格林函数、局域态密度和约化磁矩。发现局域态密度的带宽和约化磁矩与最近邻相互作用J₁、J₂及格点自旋s_a、s_b密切相关。     

Threshold resistance switching in silicon-rich SiO_x thin films

Si-rich SiO_x and amorphous Si clusters embedded in SiO_x films were prepared by the radio-frequency magnetron cosputtering method and high-temperature annealing treatment.The threshold resistance switching behavior was achieved from the memory mode by continuous bias sweeping in all films,which was caused by the formation of clusters due to the local overheating under a large electric field.Besides,the Ⅰ-Ⅴ characteristics of the threshold switching showed a dependence on the annealing temperature and the SiO_x thickness.In particular,formation and rupture of conduction paths is considered to be the switching mechanism for the 39 nm-SiO_x film,while for the 78 nm-SiO_x film,adjusting of the Schottky barrier height between insulator and semiconductor is more reasonable.This study demonstrates the importance of investigation of both switching modes in resistance random access memory.     

Interface modification and trap-type transformation in Al-doped CdO/Si-nanowire arrays/p-type Si devices by nanowire surface passivation

The present work reports the fabrication and detailed electrical properties of Al-doped CdO/Si-nanowire (SiNW) arrays/p-type Si Schottky diodes with and without SiNW surface passivation. It is shown that the interfacial trap states influence the electronic conduction through the device. The experimental results demonstrate that the effects of the dangling bonds at the SiNW surface and Si vacancies at the SiO_x/SiNW interface which can be changed by the Si–O bonding on the energy barrier lowering and the charge transport property. The induced dominance transformation from electron traps to hole traps in the SiNWs by controlling the passivation treatment time is found in this study.     

Formation of luminescent (NH4)2SiF6 phase from vapour etching-based porous silicon

In this paper we describe the formation of a luminescent (NH₄)₂SiF₆ via porous silicon (PS) obtained from HNO₃/HF vapour etching (VE) silicon (Si) substrates. It was found that at specific conditions, PS transforms in a luminescent thick white powder (WP) layer. Scanning electron microscopy (SEM) revealed that the WP has a coral-like structure. It was also found that PS persists as an intermediate layer between the Si substrate and the WP, and seems to be the seed that transforms into the WP. SEM microanalysis show that the WP is essentially composed of silicon (Si), nitrogen (N) and fluorine (F). Fourier transform infrared (FTIR) spectroscopy investigations show that this WP contains SiF₆²⁻ and NH₄⁺ ions and N---H chemical bonds. X-ray diffraction (XRD) patterns of the WP confirm that a (NH₄)₂SiF₆ cubic phase is concerned. SEM microanalyses show an excess of Si in the WP matrix. FTIR spectroscopy and XRD analysis reveal the presence of crystalline Si particles and SiO_x, both originating from the excess of Si. The (NH₄)₂SiF₆ WP phase emits an intense photoluminescence (PL) band, shifted towards higher energies as compared to the starting PS layer. The possible origin and mechanism of the luminescence emission was discussed taking into account the ability of small SiO_x-surrounded Si particles to emit PL at rather high energy. The wide range variation of the thickness of the (NH₄)₂SiF₆ WP may be easily used for the grooving of Si wafers.     

硅锗量子阱结构在硅异质结太阳电池中应用的数值模拟

利用半导体工艺和器件仿真软件silvaco TCAD(Technology Computer Aided Design),模拟研究了采用硅/硅锗合金(silicon/silicon germanium alloy,Si/Si_(1-x)Ge_x)量子阱结构作为吸收层的薄膜晶体硅异质结太阳电池各项性能.模拟结果显示,长波波段光学吸收随锗含量的增加而增加,而开路电压则因Si_(1-x)Ge_x)层带隙的降低而下降.锗含量为0.25时,短路电流密度的增加补偿了开路电压的衰减,效率提升0.2%.氢化非晶硅/晶体硅(a-Si:H/c-Si)界面空穴密度以及Si_(1-x)Ge_x)量子阱的体空穴载流子浓度制约着空穴费米能级的位置,进而影响到开路电压的大小.随着锗含量增加,a-Si:H/c-Si界面缺陷对开压的影响降低,Si_(1-x)Ge_x)量子阱的体缺陷对开压的影响则相应增加.高效率含Si_(1-x)Ge_x)量子阱结构的硅异质结太阳电池的制备需要a-Si:H/c-Si界面缺陷的良好钝化以及高质量Si_(1-x)Ge_x)量子阱的生长.     

Chemical reactions of chlorine on a vicinal Si(100) surface studied by ESDIAD

The reaction of Cl₂ on a vicinal Si(100) surface has been studied by ESDIAD. This type of surface possesses two types of sites: pairs of dangling bonds on Si---Si terrace dimers, and single dangling bonds on the 2-atom layer high steps. The reactivity of these two sites is compared. For low coverages the step dangling bonds are identified as the preferred Cl bonding site after 673 K-annealing. Upon higher temperature annealing and SiCl₂(g) desorption, the terrace-site Cl species are depleted more rapidly than the step-site Cl species. Extensive isothermal etching under a continuous Cl₂ flux at 800 K is found to produce a disordered surface structure. Heating to 1123 K causes a reordering of the surface.     

Passivation and dissociation of Pb-type defects at a-SiO_2/Si interface

It is well known that in the process of thermal oxidation of silicon,there are P_b-type defects at amorphous silicon dioxide/silicon(a-SiO_2/Si) interface due to strain.These defects have a very important impact on the performance and reliability of semiconductor devices.In the process of passivation,hydrogen is usually used to inactivate P_b-type defects by the reaction P_b+H_2→P_bH+H.At the same time,P_bH centers dissociate according to the chemical reaction P_bH→P_b+H.Therefore,it is of great significance to study the balance of the passivation and dissociation.In this work,the reaction mechanisms of passivation and dissociation of the P_b-type defects are investigated by first-principles calculations.The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band(CI-NEB)method and harmonic transition state theory(HTST).By coupling the rate equations of the passivation and dissociation reactions,the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects(P_b,P_(b0),and P_(b1))at different temperatures is calculated.     

Microstructure evolution and passivation quality of hydrogenated amorphous silicon oxide(a-SiOx:H) on〈100〉- and 〈111〉-orientated c-Si wafers

Hydrogenated amorphous silicon oxide(a-SiOx:H) is an attractive passivation material to suppress epitaxial growth and reduce the parasitic absorption loss in silicon heterojunction(SHJ) solar cells. In this paper, a-SiOx:H layers on different orientated c-Si substrates are fabricated. An optimal effective lifetime(τ(eff)) of 4743 μs and corresponding implied opencircuit voltage(iV(oc)) of 724 mV are obtained on〈100〉-orientated c-Si wafers. While τ(eff) of 2429 μs and iV_oc of 699 mV are achieved on 111-orientated substrate. The FTIR and XPS results indicate that the a-SiOx:H network consists of SiOx(Si-rich), Si–OH, Si–O–SiHx, SiO2 ≡ Si–Si, and O3 ≡ Si–Si. A passivation evolution mechanism is proposed to explain the different passivation results on different c-Si wafers. By modulating the a-SiOx:H layer, the planar silicon heterojunction solar cell can achieve an efficiency of 18.15%.     

Passivation effects of phosphorus on 4H-SiC(0001) Si dangling bonds: A first-principles study

The effect of phosphorus passivation on 4H-SiC(0001) silicon(Si) dangling bonds is investigated using ab initio atomistic thermodynamic calculations. Phosphorus passivation commences with chemisorption of phosphorus atoms at high-symmetry coordinated sites. To determine the most stable structure during the passivation process of phosphorus, a surface phase diagram of phosphorus adsorption on SiC(0001) surface is constructed over a coverage range of 1/9–1 monolayer(ML). The calculated results indicate that the 1/3 ML configuration is most energetically favorable in a reasonable environment. At this coverage, the total electron density of states demonstrates that phosphorus may effectively reduce the interface state density near the conduction band by removing 4H-SiC(0001) Si dangling bonds. It provides an atomic level insight into how phosphorus is able to reduce the near interface traps.     

钙钛矿/硅叠层太阳电池中平面a-Si:H/c-Si异质结底电池的钝化优化及性能提高

最近,旋涂法制备的钙钛矿/平面硅异质结高效叠层太阳电池引起人们广泛关注,主要原因是相比于绒面硅衬底制备的钙钛矿/硅叠层太阳电池,其制备工艺简单、制备成本低且效率高.对于平面a-Si:H/c-Si异质结电池, a-Si:H/c-Si界面的良好钝化是获得高转换效率的关键,进而决定了钙钛矿/硅异质结叠层太阳电池的性能.本文主要从硅片表面处理、a-Si:H钝化层和P型发射极等方面展开研究,通过对硅片表面的氢氟酸(HF)浸泡时间和氢等离子体预处理气体流量、a-Si:H钝化层沉积参数、钝化层与P型发射极(I/P)界面富氢等离子体处理的综合调控,获得了相应的优化工艺参数.对比研究了p-a-Si:H和p-nc-Si:H两种缓冲层材料对I/P界面的影响,其中高电导、宽带隙的p-nc-Si:H缓冲层既能够降低I/P界面的缺陷态,又可以增强P型发射层的暗电导率,提高了前表面场效应钝化效果.通过上述优化,制备出最佳的P-type emitter layer/aSi:H(i)/c-Si/a-Si:H(i)/N-type layer (inip)结构样品的少子寿命与implied-Voc分别达到2855μs和709 mV,表现出良好的钝化效果.应用于平面a-Si:H/c-Si异质结太阳电池,转换效率达到18.76%,其中开路电压达到681.5 mV,相对于未优化的电池提升了34.3 mV.将上述平面a-Si:H/c-Si异质结太阳电池作为底电池,对应的钙钛矿/硅异质结叠层太阳电池的开路电压达到1780 mV,转换效率达到21.24%,证明了上述工艺优化能够有效地改善叠层太阳电池中的硅异质结底电池的钝化及电池性能.     

CaTiO3基微波介质陶瓷的频率温度稳定性

通过对克劳修斯-莫索蒂方程的近似, 分析了钙钛矿结构微波介质陶瓷频率温度系数 (τ_f) 的主要影响因素, 发现改变材料介电响应中离子位移极化和电子位移极化的比例, 可调节频率温度系数的正负与大小. 通过电子结构计算和容忍因子分析, 预测引入(Zn_1/3Nb_2/3)⁴⁺对具有正温度系数 的CaTiO₃进行B位取代将提高材料电子极化响应比例, 调节τ_f由正变负. 采用偏铌酸盐为前驱体, 通过固相反应法合成了Ca[(Zn_1/3Nb_2/3)_xTi_(1-x)]O₃钙钛矿结构陶瓷, 并对其进行结构分析和性能测试, 实验结果与理论分析一致, 获得了具有近零频率温度系数的Ca[(Zn_1/3Nb_2/3)_0.7Ti_0.3]O₃介质陶瓷材料. 关键词： B位复合钙钛矿陶瓷 谐振频率温度稳定性 极化机理 6八面体倾斜')" href="#">BO₆八面体倾斜     

基于Cu/SiO_x/Al结构的阻变存储器多值特性及机理的研究

采用氧化硅材料构建了Cu/SiOx/Al的三明治结构阻变存储器件.用半导体参数分析仪对其阻变特性进行测量,结果表明其具有明显的阻变特性,并且通过调节限制电流,得到了四个稳定的阻态,各相邻阻态的电阻比大于10,并且具有良好的数据保持能力.在不同温度条件下对各个阻态进行电学测试及拟合,明确了不同阻态的电子传输机理不尽相同:阻态1和阻态2为欧姆传导机制,阻态3为P-F(Pool-Frenkel)发射机制,阻态4为肖特基发射机制.根据电子传输机制,建立了铜细丝导电模型并对Cu/SiOx/Al阻变存储器件各个阻态的电致阻变机制进行解释.     

Enhancement of the emission yield of silicon nanocrystals in silica due to surface passivation

The ability of surface passivation to enhance the photoluminescence (PL) emission of Si nanocrystals in SiO₂ has been investigated. Silicon precipitation in implanted samples takes place in a time scale of few minutes at 1100°C. For longer annealing at the same temperature, the PL intensity of the Si nanocrystals increases and eventually reaches saturation, while it correlates inversely with the amount of Si dangling bonds at the Si–SiO₂ interface (P_b centers), as measured by electron spin resonance. This combined behavior is independent on the silica matrix properties, implantation profiles and annealing atmosphere and duration. The observation that the light emission enhancement is directly related to the annealing of P_b centers is confirmed by treatment in forming gas. This mild hydrogenation at much lower temperature (450°C) leads to a complete passivation of the P_b defects, increasing at the same time the PL yield and the lifetime.