Ga-N共掺氧化锌纳米线阵列制备及发光性能研究

采用化学气相沉积法（CVD）以一氧化氮（NO）和氧化镓（Ga2O3）为掺杂源,在c轴取向单晶蓝宝石衬底上外延生长镓氮（Ga-N）共掺氧化锌（ZnO）纳米线阵列。利用SEM, XRD, HRTEM, XPS, PL等测试手段对掺杂后的ZnO纳米线阵列进行结构、成分和光学性能表征。结果表明,Ga-N共掺ZnO纳米线阵列保持六方纤锌矿结构,沿（002）方向择优生长;掺杂元素在样品中均匀分布。随着掺杂浓度增加,纳米线由六棱柱结构转变为尖锥层状结构,长度由2 μm减小到1 μm,锥度增加至0.95;N 1s/Ga 2p/Zn 2p峰结合能向低能态方向移动。PL光谱分析表明,所有样品均出现紫外发光峰和绿光发光峰,不同掺杂浓度的缺陷发光强度不同。     

不同V/III族元素比对m面GaN薄膜性能的影响

摘要：采用分子束外延（MBE）方法在蓝宝石衬底上外延生长m面GaN薄膜。利用原子力显微镜(AFM)、扫描电子显微镜(SEM)分析了薄膜表面形貌,对比分析结果,发现V/III族元素比从1:80降低到1:90时,外延膜表面均方根粗糙度从13.08nm降低到9.07nm。利用光谱型椭偏仪研究m面GaN薄膜,通过物理模型建立和光谱拟合得到了m面GaN薄膜的厚度、折射率和消光系数。拟合结果显示,GaN样品厚度和理论值一致,且V/III族元素比为1:90时,所得外延膜折射率较低,透射率大。两种测试方法的结果表明,V/III族元素比较小的样品晶体质量高。     

日本研制成功硅纳米线定向耦合器

日本NEC公司和日本光电子工业与技术发展协会及东京大学的科学家们第一个成功研制出Si纳米线定向耦合器。该Si纳米线定向耦合器比传统的用玻璃光纤、基于半导体SiO2或铌酸锂波导制作的定向耦合器尺寸小得多。与传统定向耦合器的几个mm的长度相比较，Si纳米线定向耦合器的总长度≤50μm。由于Si芯与SiO2包层之问的折射率差很大（分别为3．5和1．5），Si纳米线波导的S形弯曲的曲率半径小得多，所以弯曲损耗小。此外，传统的定向耦合器的典型耦合长度为几百μm或甚至为几个mm，而Si纳米线定向耦合器的耦合长度≤10μm。     

利用金作为催化剂在不同衬底上制备二氧化硅纳米线

利用金作为催化剂分别在二氧化硅及硅衬底上制备出二氧化硅纳米线。用扫描电子显微镜（SEM）及x射线光电子能谱（XPS）对纳米线进行了结构表征。SEM结果表明二氧化硅纳米线的长度为几个纳米,直径为20-150纳米。XPS结果给出硅与氧的原子比为1:2,说明所得到的为二氧化硅纳米线。二氧化硅纳米线的生长机理为气-液-固（VLS）机制。实验发现退火时间影响二氧化硅纳米线的形貌。我们也讨论了衬底对纳米线生长的影响。     

GaAs/AlGaAs核-壳结构纳米线的生长研究

GaAs/AlGaAs核-壳结构纳米线是制作金属-半导体-金属(MSM)型高速光电探测器最简洁有效的光电材料之一。采用金属有机化学气相沉积(MOCVD)设备,在GaAs(111)B衬底上开展了GaAs/AlGaAs核-壳结构纳米线的生长研究,用场发射扫描电子显微镜(SEM)和微区光荧光谱仪(PL)对制备的GaAs/AlGaAs核-壳结构纳米线样品进行了测试分析。采用已优化的GaAs/AlGaAs核-壳结构纳米线的生长工艺参数,主要研究了AlGaAs壳材料的生长机制,获得了高质量的AlGaAs壳材料,AlGaAs壳材料生长速率约为50 nm/min,Al的原子数分数为14%。这些结果为将来多异质结构纳米线的生长和光电探测器的制备奠定了基础。     

GaAs分子束外延中硅阶梯掺杂优化及C-V测量

以硅作为砷化镓分子束外延（MBE）生长中的n型掺杂剂，为了确定硅的掺杂浓度，在一片GaAs半绝缘衬底上生长多个GaAs处延层，每一层中进行不同浓度的Si掺杂，然后用电化学C—V的方法确定各层中的载流子浓度，一次性得到了不同Si掺杂浓度与Si炉的温度之间的关系曲线。本文还介绍了如何采用控制生长的条件得到陡峭的界面，使不同掺杂浓度的层与层之间的界面变化非常明显。     

硅基Ⅲ-Ⅴ族纳米线晶体管

硅基Ⅲ-Ⅴ族纳米线晶体管已经成为高速、低功耗纳米级器件的重要发展方向。首先,从气相-液相-固相生长和选择区域生长的角度,阐明了在硅衬底上无位错生长高晶体质量Ⅲ-Ⅴ族纳米线的机制。在此基础上,介绍了垂直结构和水平结构Ⅲ-Ⅴ族纳米线晶体管的制备方法。研究表明,垂直结构纳米线容易实现高密度生长,而水平结构纳米线有利于逻辑栅的制作。通过比较垂直生长、水平生长、衬底转移和自上而下纳米加工技术制备Ⅲ-Ⅴ族纳米线的工艺优缺点,为水平结构Ⅲ-Ⅴ族纳米线在硅衬底上的大面积异构集成及其器件的制作提供了新的解决方案。     

ZnO纳米线的快速生长机理及其场发射性能研究

为了快速制备具有优良场发射性能的ZnO纳米线,对ZnO纳米线的生长机理及场发射性能进行研究。首先采用优化的两步法制备出高长径比的ZnO纳米线,其次采用SEM对ZnO的微观形貌进行表征,然后,在分析形貌特点的基础上,说明了强碱体系下ZnO纳米线薄膜的快速生长机理。最后,对典型样品的场发射性能进行了测试。测试果表明,优化后的两步法,只需3h即可获得直径为40~50nm,长度为2.2~2.7μm,长径比高达54的纳米线。薄膜的开启电场为3.6V/μm,阈值场强为9.1V/um,场增强因子β高达3 391。研究表明,高pH值溶液可以加快ZnO纳米线沿C轴方向的择优生长,获得高长径比的ZnO纳米线,进而获得优良的场发射性能。     

纳米线多型异质结碳化硅室温单电子晶体管研究

采用碳化硅4H/6H多型纳米线制备单电子晶体管,在室温下观察到库仑阻塞效应和负微分电阻,I-V曲线呈现典型的库仑台阶,其台阶为周期性的,这些周期性小台阶,又呈现非周期的嵌套结构。单根纳米线碳化硅由4H/6H多型交替生长构成,它们嵌合构成竹节状生长,碳化硅多型结构中4H多型晶体构成双势垒,其直径为10⁸0nm,长度约50nm。而联结4H多型的6H多型晶体部分,长度约20nm,且直径较细(约1080nm,长度约50nm。而联结4H多型的6H多型晶体部分,长度约20nm,且直径较细(约10³5nm),被认为是库仑孤岛。     

Fe掺杂TiO_2纳米线阵列的制备及光催化性能研究

用脉冲电磁场辅助水热合成法制备了Fe掺杂TiO_2纳米线阵列,利用SEM和XRD对其形貌和物相结构进行了分析,考察了Fe掺杂TiO_2纳米线阵列对甲基橙溶液的光催化性能。结果表明:所制备的TiO_2纳米线阵列生长完好,大小均匀,结构为金红石型,但衍射峰强度低而宽,晶格发生畸变,这样会提高光催化性能。当脉冲电压为500 V,脉冲时间为60 s,脉冲频率为3 Hz时,9%(质量分数)Fe掺杂的TiO_2纳米线阵列有最强的光催化降解能力,在紫外光下照射2 h,其对浓度为0.02 g·L~(–1)的甲基橙溶液的降解率可达50.28%。     

Enhanced efficiency in GaInP/GaAs tandem solar cells using carbon doped GaAs in tunnel junction

Carbon doping of GaAs using CBr₄ (carbon tetrabromide) in metal-organic chemical vapor deposition (MOCVD) was investigated to obtain very high and sharp doping profiles required for tunnel junction in tandem solar cells. It was found that the hole concentration increased with decreasing growth temperature and V/III ratio. Hole doping profiles versus distance from the sample surface showed that the hole concentration near the surface was very low in comparison with that far below the surface. As a post-growth treatment, CBr₄ was supplied during the cool down process and produced almost constant hole concentration of 1 × 10²⁰ cm⁻³ regardless of the depth, when CBr₄ flow rate was 9.53 μmol/min. Based on these results, solar cells were fabricated using both carbon (C) and zinc (Zn) as a p-type dopant. It was shown that C doping exhibits higher efficiency and lower series resistance than those of Zn doping in GaInP/GaAs tandem solar cells.     

Growth and characteristics of p-type doped GaAs nanowire

The growth of p-type GaAs nanowires (NWs) on GaAs (111) B substrates by metal-organic chemical vapor deposition (MOCVD) has been systematically investigated as a function of diethyl zinc (DEZn) flow.The growth rate of GaAs NWs was slightly improved by Zn-doping and kink is observed under high DEZn flow.In addition,the I-V curves of GaAs NWs has been measured and the p-type dope concentration under the Ⅱ/Ⅲ ratio of 0.013 and 0.038 approximated to 1019-1020 cm-3.     

Self-catalyzed molecular beam epitaxy growth and their optoelectronic properties of vertical GaAs nanowires on Si(111)

Self-assembled GaAs nanowires were grown by molecular beam epitaxy (MBE) on un-pretreated Si(111) substrates under different As₄/Ga flux ratios (V/III ratios). It has been found that the fraction of vertical wires would be nearly 100% when the As₄/Ga ratio arrives 90. The transmission electron microscopy (TEM) and micro-photoluminescence (PL) spectra results have indicated that the GaAs nanowires grown under a larger V/III ratio (90) have a pure ZB structure. Field-effect transistors (FET) based on single nanowire were fabricated with GaAs nanowires grown under the larger V/III ratio (90). The characteristics of the FET reveal a hole concentration of 3.919×10¹⁷ cm⁻³ and a hole mobility of 0.417 cm² V⁻¹s⁻¹. Photodetectors based on single nanowire and multiple nanowires structure with a metal-semiconductor-metal (MSM) electrode configuration have been proposed and demonstrated. All the photodetectors operating at room temperature exhibit good photoconductive performance, excellent stability, reproducibility and superior peak responsivity (87.67 A/W under 5 V for single nanowire photodetector).     

A study of chemical beam epitaxy of GaAs using tris-dimethylaminoarsenic

The growth of GaAs by chemical beam epitaxy using triethylgallium and trisdimethylaminoarsenic has been studied. Reflection high-energy electron diffraction (RHEED) measurements were used to investigate the growth behavior of GaAs over a wide temperature range of 300–550°C. Both group III- and group Vinduced RHEED intensity oscillations were observed, and actual V/III incorporation ratios on the substrate surface were established. Thick GaAs epitaxial layers (2–3 μm) were grown at different substrate temperatures and V/III ratios, and were characterized by the standard van der Pauw-Hall effect measurement and secondary ion mass spectroscopy analysis. The samples grown at substrate temperatures above 490°C showed n-type conduction, while those grown at substrate temperatures below 480°C showed p-type conduction. At a substrate temperature between 490 and 510°C and a V/III ratio of about 1.6, the unintentional doping concentration is n ∼2 × 10¹⁵ cm⁻³ with an electron mobility of 5700 cm²/V·s at 300K and 40000 cm²/V·s at 77K.     

The effect of selenium doping on the optical and structural properties of Ga0.5ln0.5P

Selenium doping at an electron concentration of 10¹⁸ – 10¹⁹ cm⁻³ is shown to cause an increase in both the band gap and the disorder of Ga_0.5In_0.5P films grown by metalorganic chemical vapor deposition on GaAs substrates. The effect of selenium is shown to be very similar to that of the p-type dopants, zinc and magnesium. Selenium doping is also shown to have a dramatic smoothing effect on the surface morphology of Ga_0.5In_0.5P films.     

Growth of long wavelength infrared MCT emitters on conductive substrates

Uncooled operation of Auger suppressed fully doped mercury cadmium telluride (MCT) devices designed by Ashley and Elliott¹ and grown by metalorganic vapor phase epitaxy (MOVPE) by Maxey et al.² has been demonstrated. These devices also demonstrate efficient negative luminescent emission in the long wavelength infrared (LWIR) spectra.³ However, to operate a large area device (>1 cm²) requires a large current (∼10 A), and consequently, it is critical that the series resistance is minimized. To increase optical efficiency, deep optical concentrators are needed. Similar InSb molecular beam epitaxy (MBE) devices utilize a highly doped InSb substrate which allows a conduction path into the substrate with reduced series resistance and acts as an optical window (due to Moss-Burstein shift) allowing transmission of the 6 m IR emission. A suitable high conductivity substrate for MCT emitter devices is required to have a sheet resistivity of <1 /□. The conventional MCT epitaxy substrates are CdZnTe and GaAs. High conductivity cadmium zinc telluride (CZT) was not found to be commercially available. Although high conductivity, n-type GaAs is available, the maximum doping is limited by the degree of free carrier absorption in the LWIR which would reduce the potential emitter efficiency. This paper describes a novel investigation into achieving working LW emitter devices with deep mesas in which the current is carried by the GaAs substrate. The key issue which had to be addressed was obtaining conduction between the II/VI and III/V materials. A variety of interface designs was investigated but the best results were achieved by minimizing the band-gap of the interfacial II/VI MCT and optimizing the properties of the top region of the GaAs substrate.     

Self-aligned n-channel GaAs metal-oxide-semiconductor field-effect transistors (MOSFETs) using HfO2 and silicon interface passivation layer: Post-metal annealing optimization

In this work, using Si interface passivation layer (IPL), we demonstrate n-MOSFET on p-type GaAs by varying physical-vapor-deposition (PVD) Si IPL thickness, S/D ion implantation condition, and different substrate doping concentration and post-metal annealing (PMA) condition. Using the optimized process, TaN/HfO₂/GaAs n-MOSFETs made on p-GaAs substrates exhibit good electrical characteristics, equivalent oxide thickness (EOT) (∼3.7 nm), frequency dispersion (∼8%) and high maximum mobility (420 cm²/V s) with high temperature PMA (950 °C, 1 min) and good inversion.     

Molecular beam epitaxial growth of carbon doped GaAs with elemental gallium and arsenic sources and a CCI4 gas source

CC1₄ has been used as a carbon acceptor dopant source for GaAs grown by elemental source molecular beam epitaxy. Deposition of CC1₄ during normal arsenic stabilized growth of GaAs resulted in low mobility, p-type material. Attempts to thermally crack the CC1₄ using a heated gas cracking source resulted in an even lower hole concentration and mobility. One possible explanation for this ineffective acceptor doping behavior, relative to growth environments containing hydrogen (metalorganic chemical vapor deposition) where CC1₄ is an effective dopant, is that hydrogen plays a role in the incorporation of the carbon. Another possible explanation for the poor doping behavior is that the CC1₄ was being modified by the gas cracker, even at relatively low gas cracker temperatures. Further experimentation with different injection schemes will be necessary to better understand the doping behavior. Depositing the CC1₄ onto static, gallium-rich surfaces produces GaAs:C with hole mobilities comparable to GaAs:Be. Average hole concentrations as high as 4 x 10¹⁹ have been demonstrated. Carbon doped AlGaAs/GaAs heterojunction bipolor transistors (HBT_s) have been fabricated with the same characteristics as Be doped HBTs grown in the same MBE system.     

An Improved Theoretical Model to Explain Electronic and Optical Properties of p-Type GaAs/AlGaAs Superlattices for Multi-Wavelength Normal Incidence Photodetectors

We extend our previous theoretical analysis of electronic and optical properties of p-type quantum well structures based on the two heavy- and light-hole system to include all the three valence bands. These theories are then used to clarify the origin of the normal incidence absorption and photocurrent at photon wavelengths of 2 - 3 μm, which was observed in addition to the absorption around 8 μm by a recent experimental investigation with heavily doped p-type GaAs/AlGaAs multi-quantum well (MQW) structures. In the theoretical analysis, the Hartree and exchange-correlation many-body interactions are taken into account within one-particle local density approximation, and it is shown that normal incidence absorption occurs in two wavelength regions over the transition energy range higher than barrier height for p-type GaAs/AlGaAs superlattices with well doping of 2 × 10¹⁹ cm⁻³; one region has broad absorption peaks with coefficients of about 5000 cm⁻⁻¹ around 8 μm, and the other has two rather sharp peaks at 2.7 μm and 3.4 μm with 1800 cm⁻⁻¹ and 1300 cm⁻⁻¹, respectively. The result indicates that the theory explains the experimental observation well, as the theoretical and experimental results are in close agreement in general absorption features.     

A Roadmap for Controlled and Efficient n‐Type Doping of Self‐Assisted GaAs Nanowires Grown by Molecular Beam Epitaxy

N‐type doping of GaAs nanowires has proven to be difficult because the amphoteric character of silicon impurities is enhanced by the nanowire growth mechanism and growth conditions. The controllable growth of n‐type GaAs nanowires with carrier density as high as 10²⁰ electron cm^?3 by self‐assisted molecular beam epitaxy using Te donors is demonstrated here. Carrier density and electron mobility of highly doped nanowires are extracted through a combination of transport measurement and Kelvin probe force microscopy analysis in single‐wire field‐effect devices. Low‐temperature photoluminescence is used to characterize the Te‐doped nanowires over several orders of magnitude of the impurity concentration. The combined use of those techniques allows the precise definition of the growth conditions required for effective Te incorporation.