掺稀土半导体光电特性和应用

结合我们近年来在掺稀土硅基材料和Ⅲ-Ⅴ族化合物半导体材料的发光研究，简述目前国际上在这方面研究的新进展，重点介绍掺铒硅基发光和掺稀土GaN发光材料和器件的研究结果。     

不同条件对扩镓硅基GaN晶体膜质量影响的XRD分析

采用射频磁控溅射工艺在扩镓硅基上溅射Ga2O3薄膜氮化反应组装GaN晶体膜,并对其生长条件进行研究。用XRD对样品进行了结构分析,测试结果表明：采用此方法得到的预沉积的扩镓硅基生长GaN晶体膜随着扩镓时间和氮化时间的增加,薄膜的晶化程度得到明显提高。     

扩镓硅基GaN晶体膜质量的电镜分析

采用射频磁控溅射工艺在扩镓硅基上溅射Ga2O3薄膜,氮化反应组装GaN晶体膜,并对其生长条件进行研究．用扫描电镜(SEM)和X射线衍射(XRD)对样品进行结构、形貌分析．观测结果表明：采用此方法得到的在预沉积扩镓硅基上生长的GaN晶体膜,随着扩镓时间的增加,薄膜的晶化程度得到明显提高,而氮化时间对构成GaN薄膜的颗粒形态影响不大．     

一种黄绿光LED用荧光粉:Ga_2S_3∶Eu~(2 )

用GaN基发光二极管(light-emitting diode,LED)与稀土发光材料组成的固体照明光源具有节能、寿命长、光效高、工作电压低、耗电量小、体积小、可平面封装、易于开发轻薄型产品等特点,被认为是21世纪的光源;另外,LED光源本身不含汞、     

黄光类水滑石的制备、表面改性及应用

采用共沉淀法合成了荧光类水滑石材料,该材料在470 nm蓝光激发下可发出黄色荧光(557 nm),采用硅烷偶联剂对其进行表面改性,探讨了表面改性对黄光类水滑石的发光性能、结构及热稳定性的影响。将改性黄光类水滑石与GaN基蓝光芯片封装后制得了白光LED。研究结果表明,改性的黄光类水滑石是制作白光LED可供选用的黄色发光材料。本文成功地将低温一步法制备得到的金属有机配合物/无机纳米杂化材料应用于LED,拓展了LED用荧光粉的选用范围。     

黄光类水滑石的制备、表面改性及应用

采用共沉淀法合成了荧光类水滑石材料,该材料在470 nm蓝光激发下可发出黄色荧光(557 nm),采用硅烷偶联剂对其进行表面改性,探讨了表面改性对黄光类水滑石的发光性能、结构及热稳定性的影响。将改性黄光类水滑石与GaN基蓝光芯片封装后制得了白光LED。研究结果表明,改性的黄光类水滑石是制作白光LED可供选用的黄色发光材料。本文成功地将低温一步法制备得到的金属有机配合物/无机纳米杂化材料应用于LED,拓展了LED用荧光粉的选用范围。     

利用Pd催化合成单晶GaN纳米线的光学特性(英文)

基于金属元素钯具有的催化特性,采用射频磁控溅射方法,在Si(111)衬底上沉积Pd:Ga2O3薄膜,然后在950℃下对薄膜进行氨化,制备出大量GaN纳米线.采用扫描电子显微镜(SEM)、X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等技术手段对样品的结构、形貌和成分进行分析.结果表明,制备的样品为具有六方纤锌矿结构的单晶GaN纳米线,直径在20-60nm范围内,长度为几十微米,表面光滑无杂质,结晶质量较高.用光致发光光谱对样品的发光特性进行测试,分别在361.1、388.6和426.3nm处出现三个发光峰,且与GaN体材料相比近带边紫外发光峰发生了较弱的蓝移.对GaN纳米线的生长机制也进行了简单的讨论.     

氮化镓生长系统中源区反应的热力学分析和实验研究

本文报道化学气相淀积法生长GaN薄膜材料的Ga-HCl-NH₃载气体系的源区反应热力学分析和实验研究结果.     

群分解EHMO计算机程序的编制及GaN晶体能谱的计算

本文把变换算符对原子轨道的作用概括成两个法则,还给出了一个求属于某个高阶不可约表示的基分子轨道的简便方法,即用投影算符求出其中一个分子轨道,然后用这个轨道在变换算符作用下的变换性质来求其余的分子轨道。用这种算法编制EHMO计算机程序在文中也作了扼要的说明。作为程序应用的示例,计算了GaN“分子簇”(包括不同原子数目、掺杂和空位等各种情况)的单电子能级,为实验工作者对GaN(Zn)中什么是施主和什么是受主的推测提供了量子化学的解释。     

利用高分辨X射线衍射仪表征GaN薄膜的结构特性

使用高分辨X射线衍射法（HRXRD）对金属有机物化学气相沉积（MOCVD）外延生长GaN薄膜进行微结构表征．首先采用绝对测量法精确测试了GaN薄膜的晶格常数,由此获得该GaN薄膜的应变与弛豫的信息．采用面内掠入射（IP—GID）法测定了GaN薄膜的位错密度以及位错扭转角．     

Intrinsic Properties of Macroscopically Tuned Gallium Nitride Single-Crystalline Facets for Electrocatalytic Hydrogen Evolution

The anisotropy of crystalline materials results in different physical and chemical properties on different facets, which warrants an in-depth investigation. Macroscopically facet-tuned, high-purity gallium nitride (GaN) single crystals were synthesised and machined, and the electrocatalytic hydrogen evolution reaction (HER) was used as the model reaction to show the differences among the facets. DFT calculations revealed that the Ga and N sites of GaN (100) had a considerably smaller ΔG_H* value than those of the metal Ga site of GaN (001) or N site of GaN (00−1), thereby indicating that GaN (100) should be more catalytically active for the HER on account of its nonpolar facet. Subsequent experiments testified that the electrocatalytic performance of GaN (100) was considerably more efficient than that of other facets for both acidic and alkaline HERs. Moreover, the GaN crystal with a preferentially (100) active facet had an excellently durable alkaline electrocatalytic HER for more than 10 days. This work provides fundamental insights into the exploration of the intrinsic properties of materials and designing advanced materials for physicochemical applications.     

Tailoring GaN semiconductor surfaces with biomolecules

Functionalization of semiconductors constitutes a crucial step in using these materials for various electronic, photonic, biomedical, and sensing applications. Within the various possible approaches, selection of material-binding biomolecules from a random biological library, based on the natural recognition of proteins or peptides toward specific material, offers many advantages, most notably biocompatibility. Here we report on the selective functionalization of GaN, an important semiconductor that has found broad uses in the past decade due to its efficient electroluminescence and pronounced chemical stability. A 12-mer peptide ("GaN_probe") with specific recognition for GaN has evolved. The subtle interplay of mostly nonpolar hydrophobic and some polar amino acidic residues defines the high affinity adhesion properties of the peptide. The interaction forces between the peptide and GaN are quantified, and the hydrophobic domain of the GaN_probe is identified as primordial for the binding specificity. These nanosized binding blocks are further used for controlled placement of biotin-streptavidin complexes on the GaN surface. Thus, the controlled grow of a new, patterned inorganic-organic hybrid material is achieved. Tailoring of GaN by biological molecules can lead to a new class of nanostructured semiconductor-based devices.     

Epitaxy of AIN and GaN thin films on silicon or sapphire for the development of high frequency saw devices

The increase in operating frequencies of telecommunication systems requires to use Surface Acoustic Wave (SAW) devices for filtering applications that propagate on “high velocity” subtrates like sapphire or even <100 > silicon. The excitation of SAW on such materials requires using thin piezoelectric layers deposited on their top surface, like AIN or GaN. This paper is devoted to the theoretical and experimental study of such material combinations. The theoretical models for multimaterial substrates are first presented. Experimental results are then reported, allowing to define the application field of AIN or GaN thin-film based devices.     

Vapor Phase Epitaxy of Nitride Films

GaN and related compounds are very promising materials for developing short wavelength light emitting devices, such as laser diode (LD) and light emitting diode (LED), high temperature and high power electronics. Commercially used nitride materials have been made by vapor phase epitaxy (VPE), including metalorganic vapor phase epitaxy (MOVPE) and hydride vapor phase epitaxy (HVPE). MOVPE is a widely used technique to fabricate semiconductor films. Its precise control of growth process, ability of handling multi large area wafers, and excellent reproducibility make it valuable in large-scale production of electronic and optoelectronic devices. VPE of nitrides has met several critical materials issues. Firstly, a high vapor pressure of nitrogen leads to the lack of bulk crystal of GaN. People have to use heteroepitaxy technique to produce GaN materials and devices, which makes high-density defects in GaN epilayers. Secondly, the high bonding energy of GaN and high stability of NH₃ require a high growth temperature. The high nitrogen vapor pressure at high growth temperature requires enhanced local precursor densities. Additionally, the growth chemistry of VPE of nitride materials is very complicated. Parasitic chemical reactions take place during the VPE growth and degrade the material quality. Finally, the physical process of VPE growth has not been well understood. Optimized production of nitride material is predicated on an understanding of how the film properties are affected by the initial processing sequence. Heteroepitaxy of nitrides is strongly influenced by the initial nucleation and growth sequence.     

Ag作催化剂制备的GaN的形貌及其性能

用化学气相沉积法(CVD)在Si(100)衬底上以Ag纳米颗粒为催化剂制备了微纳米结构的GaN,原料是熔融态的金属Ga和气态的NH3。采用X射线衍射仪(XRD)、透射电镜(TEM)、X-ray能谱仪(EDS)、场发射扫描电子显微镜(SEM)、光致发光能谱(PL)和霍尔效应测试对样品进行了结构、成分、形貌和发光、电学性能分析。结果表明:生成的自组装GaN为六方纤锌矿的类似小梯子的微纳米单晶结构,且在不同的温度下,GaN的发光性能和电学性能也有所不同,相对于强的紫外发光峰,其它杂质发光峰很微弱,且均呈p型导电。对本实验所得到的GaN微纳米结构的可能形成机理进行了探讨。     

A structural analysis of ultrathin barrier (In)AlN/GaN heterostructures for GaN-based high-frequency power electronics

Metal–organic chemical vapor deposition (MOCVD) is one of the best growth methods for GaN-based materials as well-known. GaN-based materials with very quality are grown the MOCVD, so we used this growth technique to grow InAlN/GaN and AlN/GaN heterostructures in this study. The structural and surface properties of ultrathin barrier AlN/GaN and InAlN/GaN heterostructures are studied by X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements. Screw, edge, and total dislocation densities for the grown samples have been calculated by using XRD results. The lowest dislocation density is found to be 1.69 × 10⁸ cm⁻² for Sample B with a lattice-matched In_0.17Al_0.83N barrier. The crystal quality of the studied samples is determined using (002) symmetric and (102) asymmetric diffractions of the GaN material. In terms of the surface roughness, although reference sample has a lower value as 0.27 nm of root mean square values (RMS), Sample A with 4-nm AlN barrier layer exhibits the highest rough surface as 1.52 nm of RMS. The structural quality of the studied samples is significantly affected by the barrier layer thickness. The obtained structural properties of the samples are very important for potential applications like high-electron mobility transistors (HEMTs).     

Physical and electrical properties of chemical vapor grown GaN Nano/microstructures

Wurtzitic gallium nitride nano- and microleaves were controlled grown through a facile chemical vapor deposition method. This is the first report of GaN nanoleaves, a new morphology of GaN nanostructures. The as-grown GaN structures were characterized by means of X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, transmission electron microscopy, and selected area electron diffraction. Raman scattering spectra of the GaN leaves were studied. Field effect transistors based on individual GaN nanoleaves were fabricated, and the electrical transport results revealed a pronounced n-type gating effect of the GaN nanostructures.     

不同金属缓冲层对GaN薄膜的光学及电学性能的影响

本文以金属Ga和NH3为原料,Al、Ni和Fe为金属缓冲层,采用化学气相沉积法(CVD)在Si(100)衬底上合成了GaN微米薄膜。利用X射线衍射仪(XRD)、场发射扫描电子显微镜(FESEM)、能量弥散X射线谱(EDS)、光致发光光谱(PL)和霍尔效应测试仪(HMS-3000)等对GaN微米薄膜进行表征。结果表明,所有样品均为六方纤锌矿结构;样品均出现了很强的近带边紫外发射峰和半峰宽较大的中心波长为672 nm红光发射峰;不同样品的电学性能差异较大。最后对合成的GaN微米薄膜的可能形成机理进行了简单分析。     

Nanotubes and nanowires

Synthesis and characterization of nanotubes and nanowires constitute an important part of nanoscience since these materials are essential building units for several devices. We have prepared aligned carbon nanotube bundles and Y-junction nanotubes by the pyrolysis of appropriate organic precursors. The aligned bundles are useful for field emission display while the Y-junction nanotubes are likely to be useful as nanochips since they exhibit diode properties at the junction. By making use of carbon nanotubes, nanowires of metals, metal oxides and GaN have been obtained. Both the oxide and GaN nanowires are single crystalline. Gold nanowires exhibit plasmon bands varying markedly with the aspect ratio. GaN nanowires show excellent photoluminescence characteristics. It has been possible to synthesise nanotubes and nanowires of metal chalcogenides by employing different strategies.     

N2流量对GaN的形貌及光学和电学性能的影响

采用化学气相沉积法(CVD)在Si(100)衬底上以Ni为催化剂, 金属Ga和NH₃为原料合成了GaN微纳米结构, 并研究了N₂流量对产物GaN的形貌及光学和电学性能的影响。利用场发射扫描电子显微镜(SEM)、透射电镜(TEM)、X射线衍射仪(XRD)、X-ray能谱仪(EDS)、光致发光谱(PL)和霍尔效应测试仪(HMS-3000)等测试手段对样品的形貌、结构、成分、光学和电学性能进行了分析。结果表明, 随着N₂流量的增加, 产物GaN的形貌发生了由微米棒到蠕虫状线再到光滑纳米线的转变;生成的GaN均为六方纤锌矿结构;样品均表现出383 nm的近带边紫外发射峰和470 nm左右的蓝光发射峰;所有样品均为n型;并对产物GaN的形貌转变机理进行了分析。