红外光电子材料碲镉汞异质外延结构理论研究

文章介绍了基于第一性原理的LAPW方法就Hg空位缺陷对碲镉汞材料的电子结构的影响进行了研究。首先选择Hg0. 5 Cd0. 5 Te体系详细分析了Hg空位引起的弛豫,包含Hg空位缺陷体系的电荷密度、成键电荷密度和态密度,得到了碲镉汞材料形成Hg空位情况下的空位第一近邻阴离子悬挂键重整的形式以及Hg空位所形成的双受主能级。计算发现了Hg空位引起第一近邻Te原子5s态能级向高能端移动的现象。 同时,对实验中通常利用As钝化基底表面来有效地控制外延生长的极性进行了研究。本文也介绍了基于密度泛函理论模拟了单个及多个As原子在Si (211)重构表面上的吸附、置换行为,通过系统地计算各种可能的吸附、置换构型,并进一步分析能量、键长等性质,对As在Si(211)表面的钝化机理进行了初步研究探讨。对Cd、Te在As钝化前后Si (211)表面上的吸附行为也进行了研究分析,为外延生长实验中利用As钝化来保证B 面极性的做法提供了一定的理论依据。     

Si(100)—As表面钝化作用和氧吸附

利用自己研制的具有分子束外延系统的表面分析联合谱仪研究了氧与Si(100)—As表面的相互作用。本文进一步证实了As层是Si表面的很好的钝化层,并首次研究了Si(100)—As表面的氧吸附全过程。实验表明,氧的饱和覆盖量为0.5单原子层,即Si表面上存在As原子层而使吸附位置减少一半。另外,通过吸附动力学分析得知,Si(100)—As表面的初始粘附系数是5.6×10~(-3),比清洁的Si(100)表面小一个数量级。Si表面上As的钝化作用是Si原子的悬挂键态被As原子的占有孤立对态代替而形成。     

Co在Si(100)表面化学吸附的电子结构和性质

用紧束缚下的Muffin-tin轨道线性组合方法研究了单层Co原子在理想的Si(100)表面的化学吸附.计算了Co原子在不同位置时吸附体系的能量.结果表明,Co原子在C位(四度位)时吸附最稳定,在Co/Si(100)界面存在Co、Si混合层.同时对电子转移情况和层投影态密度进行了研究.     

Co在Si(100)表面化学吸附的电子结构和性质

用紧束缚下的Muffin tin轨道线性组合方法研究了单层Co原子在理想的Si(10 0 )表面的化学吸附.计算了Co原子在不同位置时吸附体系的能量.结果表明,Co原子在C位(四度位)时吸附最稳定,在Co/Si(10 0 )界面存在Co、Si混合层.同时对电子转移情况和层投影态密度进行了研究.     

阳极氧化膜对光伏探测器的钝化作用

本文根据对阳极氧化膜与(Hg、Cd)Te界面特性的电子能谱和MIS C-V测试结果,讨论了用阳极氧化膜作光伏探测器钝化膜的可能性。提出了在(Hg、Cd)Te表面先生长一层约0.01μm阳极氧化膜作表面预处理的新设想。(Hg、Cd)Te为衬底的探测器目前常规使用的钝化膜有阳极氧化膜ZnS和SiO_2及它们     

n-HgCdTe光导器件的两种表面钝化研究

利用 Ar 束溅射沉积技术实现了 Cd Te薄膜的低温生长 ,利用电化学方法进行了 Hg Cd Te表面自身阳极氧化膜的生长 ,利用生长的 Cd Te介质膜和 Hg Cd Te表面自身阳极氧化膜对 n- Hg Cd Te光导器件进行了表面钝化 .对两种器件的电阻、各项性能指标进行了测量分析 ,实验表明得到的 Cd Te/ Hg Cd Te界面质量已达到器件实用化水平 .     

氢在GaAs(110)表面吸附的研究

采用EHMO方法计算了氢在GaAs(110)表面的吸附,确定了氢原子在表面的吸附位置.计算结果表明,Ga与As都能吸附氢原子,最稳定的吸附位置在As的悬键位,其次为Ga的悬键位;氢与表面原子形成共价键,键长均约为1.32A|°.当氢原子吸附于As的悬键位时,禁带中出现由As原子及Ga原子引入的表面态.同时计算表明GaAs(110)表面不能吸附分子态的氢,与已知的实验结果相符.     

Mg在Si(100)-2?1表面的化学吸附

用紧束缚下的Muffin-tin轨道线性组合方法研究了0.5个单层Mg原子在Si(100)-(2×1)表面的化学吸附。计算了Mg 原子在不同位置时吸附体系的能量。结果表明,Mg原子在吸附面上方的cave位吸附最稳定,同时在吸附面上方还存在一个亚稳位置shallow位,这与实验结果一致。同时对电子转移情况和层投影态密度进行了研究。     

Ni在Si(111)和Si(100)面上吸附的理论研究

采用集团模型和分立变分的 Xα方法研究 Ni原子在Si(111)顶位和三度开位吸附,以及在Si(100)四度位和桥位吸附的可能性,由体系的总能量最低确定稳定吸附位置,并在稳定吸附位讨论了Ni-Si成键特性和态密度.结果表明,只有当Si(111)表面弛豫情况下Ni原子才能沿[111]方向进入表面以下,但Ni原子也能沿[100]方向进入Si表面层.计算所得态密度与实验符合较好.比较所得的态密度和 NiSi_2/Si(111)的界面态密度表明位于表面下的Ni可能是生长NiSi_2的先兆.     

砷化镓和直拉硅单晶中微沉淀物的EDS和EELS检测

(一)砷化镓单晶中微沉淀物的EDS检测在早期的工作中曾对Ga As:Te和Ga As:Si中微缺陷的结构性质及其与杂质浓度的关系作了TEM研究,结果表明在保持单晶砷化镓结构完整性上,Si是一种远优越于Te的掺杂剂。这不仅表现在Ga As:Si中引起缺陷出现的临界Si电子浓度要比Te高一个数量级,而且还表现在Ga As:Si中的缺陷密度低,尺寸小,分立     

CdZnTe heteroepitaxy on 3″ (112) Si: Interface, surface, and layer characteristics

Tellurium adsorption studies were made on clean and arsenic passivated (112) silicon surfaces. Quantitative surface coverage values for tellurium were determined by Auger electron spectroscopy. Saturation coverage of up to 1.2 monolayers of tellurium could be obtained on a clean (112) silicon surface. On an arsenic passivated (112) Si surface however, the tellurium saturation coverage was limited to only ∼0.3 monolayer. Analysis of the adsorption behavior suggested that tellurium and arsenic chemisorption occurs preferentially at step edges and on terraces, respectively. The study revealed that arsenic passivation led to a significant decrease in the sticking coefficient of tellurium and an increase in it’s surface mobility. A model describing zinc telluride nucleation on a (112) Si surface is proposed. Thin templates of ZnTe followed by Cd_1−xZn_xTe layers were deposited on (112) Si by molecular beam epitaxy (MBE). The characteristics of the MBE Cd_1−xZn_xTe layers were found to be sensitive to the initial ZnTe nucleation and Si surface preparation.     

Selective Growth of CdTe on Si(211): First-Principle Calculations

The adsorption of CdTe layers on clean and As-passivated Si(211) substrates has been simulated by first-principle calculations in this study. Based on the simulation results, we theoretically show the important roles of the As₄ passivation during the epitaxial growth. Arsenic can saturate part of the dangling bonds and weaken the surface states. The partial passivation finally induces the B-face polarity selection automatically. This conclusion can provide further explanations for the successful growth of large area high-quality CdTe(211)B layers on the Si(211) substrates.     

Arsenic deposition as a precursor layer on silicon (211) and (311) surfaces

We investigate the properties of arsenic (As) covered Si(211) and Si(311) surfaces by analyzing data from x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED) images. We then create a model using total surface energy calculations. It was found that both Si(211) and Si(311) had 0.68±0.08 surface As coverage. Si(211) had 0.28±0.04 Te coverage and Si(311) had 0.24±0.04 Te coverage. The Si(211) surface replaces the terrace and trench Si atoms with As for a lower surface energy, while the Si edge atoms form dimers. The Si(311) surface replaces all terrace atoms and adsorbs an As dimer every other edge site. These configurations imply an improvement in the mean migration path from the bare silicon surface by allowing the impinging atoms for the next epitaxial layer, tellurium (Te), to bind at every other pair of edge atoms, and not the step terrace sites. This would ensure a nonpolar, B-face growth.     

Effect of As Passivation on Vapor-Phase Epitaxial Growth of Ge on (211)Si as a Buffer Layer for CdTe Epitaxy

We report an investigation of epitaxial germanium grown by chemical vapor deposition (CVD) on arsenic-terminated (211)Si, which is the preferred substrate in the USA for fabrication of night-vision devices based on mercury cadmium telluride (MCT) grown by molecular-beam epitaxy (MBE). The films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), cross-sectional transmission electron microscopy (XTEM), and x-ray diffraction (XRD). Arsenic passivation was found to be effective in preventing cross-contamination of unwanted residual species present inside the reactor chamber and also in prolonging the evolution of layer-by-layer growth of Ge for significantly more monolayers than on nonpassivated Si. The two-dimensional (2D) to three-dimensional (3D) transition resulted in Ge islands, the density and morphology of which showed a clear distinction between passivated and nonpassivated (211)Si. Finally, thick Ge layers (∼250 nm) were grown at 525°C and 675°C with and without As passivation, where the layers grown with As passivation resulted in higher crystal quality and smooth surface morphology.     

Cleaning and passivation of the Si(100) surface by low temperature remote hydrogen plasma treatment for Si epitaxy

This paper presents the results of a study of the hydrogen-passivated Si(100) surface prepared by a remote hydrogen plasma treatment which serves the dual purpose of cleaning and passivating the Si(100) surface prior to low temperature Si epitaxy by Remote Plasma-enhanced Chemical Vapor Deposition (RPCVD). The remote hydrogen plasma treatment was optimized for the purposes of cleaning and passivation, respectively. To achieve a clean, defect-free substrate surface, the remote hydrogen plasma process was first optimized using Transmission Electron Microscopy (TEM) and Auger Electron Spectroscopy (AES). For hydrogen passivation, the substrate temperature was varied from room temperature to 250° C in order to investigate the degree of passivation as a function of substrate temperature by examining the amount of oxygen readsorbed on the substrate surface after air exposure. Low temperature Si expitaxy was subsequently performed on the air-exposed substrates without further cleaning to evaluate the effectiveness of the hydrogen passivation. It was found that better Si surface passivation is achieved at lower substrate temperatures as evidenced by the fact that less oxygen is observed on the surface using AES and Secondary Ion Mass Spectroscopy (SIMS) analyses. The amount of readsorbed oxygen on the H-passivated Si surface after a two hour air exposure was found to be as low as 0.1 monolayer from SIMS analysis. Using Reflection High Energy Electron Diffraction (RHEED) analysis, different surface reconstructions ((3 × 1) and (1 × 1)) were observed for H-passivated Si surfaces passivated at various temperatures, which was correlated to the results of AES and SIMS analyses. Epitaxial growth of Si films at 305° C was achieved on the air-exposed Si substrates, indicating a chemically inert Si surface as a result of hydrogen passivation. A novel electron-beam-induced-oxygen-adsorptiom phenomena was observed on the Hpassivated Si surface. Scanning Auger Microscopy (SAM) analysis was performed to study the reaction kinetics as well as the nature of Si—H bonds on the H-passivated Si surface. Preliminary results show that there is a two-step mechanism involved, and oxygen adsorption on the H-passivated Si surface due to electron beam irradiation may be due to the formation of O-H groups rather than the creation of Si—O bonds.     

Methylthiol adsorption on GaAs(100)-(2 × 4) surface: Ab initio quantum-chemical analysis

Quantum-chemical cluster calculations within the density functional theory are performed to study the mechanism of adsorption of the methylthiol molecule CH₃SH on an As-As dimer on a GaAs (100) surface. It is shown that the adsorption of the molecule can proceed through dissociation of either the S-H or C-S bond. The lowest energy has the state of dissociative adsorption with the rupture of the C-S bond resulting in the formation of a methane molecule and sulfur adatom incorporated between surface arsenic atoms constituting the dimer. A somewhat higher energy has the state of dissociative adsorption with the rupture of the S-H bond. In this state the CH₃S-radical is adsorbed at an arsenic atom constituting dimer and the hydrogen atom is adsorbed at a gallium atom bonded to this arsenic atom. These two states provide chemical and electronic passivation of the semiconductor surface.     

制备及钝化条件对多孔硅发光性能的影响

研究了氧化电流密度对多孔硅（PS）PL谱的影响。结果表明，随着氧化电流密度增大，PS的微晶Si平均尺寸减小，且尺寸的微晶Si数量也减少，说明制备条件对钝化PS的发光有影响；PS经适当的高温氧化处理后，其PL谱会发生明显变化；选用含有胺基的正丁胺，采用射频辉光放电法对PS进行钝化处理，在一定程度上提高了PS的发射强度伴随发光峰值的较大蓝移；其钝化PS的荧光谱随钝化温度和钝化时间变化，说明钝化条件对钝化PS的发光有直接影响。由此，可以通过调节制备和钝化条件来获得最大的发光效率和所需要的发光颜色。     

表面活性剂对硅单晶片表面吸附颗粒的作用

提出了新抛光硅片镜面吸附动力学过程;深入研究表面活性剂的性质和作用,利用表面活性剂特性,有效地控制硅片表面颗粒处于易清洗的物理吸附状态。