Effect of the thickness of InGaN interlayer on a-plane GaN epilayer

In this paper,we use the a-plane InGaN interlayer to improve the property of a-plane GaN.Based on the a-InGaN interlayer,a template exhibits that a regular,porous structure,which acts as a compliant effect,can be obtained to release the strain caused by the lattice and thermal mismatch between a-GaN and r-sapphire.We find that the thickness of InGaN has a great influence on the growth of a-GaN.The surface morphology and crystalline quality both are first improved and then deteriorated with increasing the thickness of the InGaN interlayer.When the InGaN thickness exceeds a critical point,the a-GaN epilayer peels off in the process of cooling down to room temperature.This is an attractive way of lifting off a-GaN films from the sapphire substrate.     

A Simple Route of Morphology Control and Structural and Optical Properties of ZnO Grown by Metal-Organic Chemical Vapour Deposition

Employing the metal-organic chemical vapour deposition （MOCVD） technique, we prepare ZnO samples with different morphologies from the film to nanorods through conveniently changing the bubbled diethylzinc flux （BDF） and the carrier gas flux of oxygen （OCGF）. The scanning electron microscope images indicate that small BDF and OCGF induce two-dimensional growth while the large ones avail quasi-one-dimensional growth. X-ray diffraction （XRD） and Raman scattering analyses show that all of the morphology-dependent ZnO samples are of high crystal quality with a c-axis orientation. From the precise shifts of the 20 locations of ZnQ （002） face in the XRD patterns and the E2 （high） locations in the Raman spectra, we deduce that the compressive stress forms in the ZnO samples and is strengthened with the increasing BDF and OCGF. Photoluminescence spectroscopy results show all the samples have a sharp ultraviolet luminescent band without any defects-related emission. Upon the experiments a possible growth mechanism is proposed.     

MOCVD生长温度对氧化锌薄膜结构及发光性能的影响

利用甲醇做氧源,采用金属有机物化学气相沉积(MOCVD)工艺在硅(111)衬底上生长了一系列的氧化锌薄膜,生长温度为400～600℃。薄膜的表面形貌及晶体质量分别利用场发射扫描电镜及X射线衍射仪进行了测量。研究表明:随着生长温度的降低,在X射线衍射图谱中氧化锌(101)峰取代了(002)峰成为了主峰。这可能是由于温度过低使得甲醇未完全分解,而甲醇分子抑制了氧化锌沿c轴极性过快的生长所致。室温光致发光光谱结果表明在较高生长温度下获得的样品具有良好的光学性质,发光强度随着温度的降低而降低。     

Effects of V/III ratio on a-plane GaN epilayers with an InGaN interlayer

The effects of V/Ill growth flux ratio on a-plane GaN films grown on r-plane sapphire substrates with an InGaN interlayer are investigated. The surface morphology, crystalline quality, strain states, and density of basal stacking faults were found to depend heavily upon the V/III ratio. With decreasing V/III ratio, the surface morphology and crystal quality first improved and then deteriorated, and the density of the basal-plane stacking faults also first decreased and then increased. The optimal V/III ratio growth condition for the best surface morphology and crystalline quality and the smallest basal-plane stacking fault density of a-GaN films are found. We also found that the formation of basal-plane stacking faults is an effective way to release strain.     

磁控溅射ZrN薄膜的生长机理及光学性能

利用直流反应磁控溅射法在Si衬底上沉积了高结晶质量的氮化锆(ZrN)薄膜。采用X射线衍射仪(XRD)、场发射扫描电子显微镜(FE-SEM)、原子力显微镜(AFM)和光谱椭偏仪(SE)研究了沉积时间对ZrN薄膜结构、表面形貌和光学性能的影响。结果表明:所沉积薄膜均为NaCl结构的立方相ZrN,具有(111)面单一取向;沉积时间的增加提高了薄膜的结晶质量;ZrN薄膜的表面形貌、晶粒尺寸以及表面粗糙度随沉积时间发生变化,沉积45 min的薄膜表面出现致密的三角锥晶粒,且表面粗糙度最大,薄膜呈柱状生长。随后利用Extend Structure Zone Model解释了ZrN薄膜的生长机制,最后研究了ZrN薄膜的光反射特性,发现反射光谱与晶粒形状和表面粗糙度密切相关,表面具有三角锥状晶粒的薄膜,其反射谱在300~800 nm波长范围内存在振荡现象,相比于具有不规则晶粒形貌的薄膜其反射率明显下降。本文中研究的生长条件与晶体结构、微观形貌和光学性能之间的关系,可为器件中应用的ZrN薄膜最佳制备条件的优化提供重要的参考价值。     

离子能量和沉积温度对离子束沉积碳膜表面形貌的影响

利用质量分离的低能离子束沉积技术,得到了非晶碳膜.所用离子能量为50—200eV,衬底温度从室温到800℃.在沉积的能量范围内,衬底为室温时薄膜为类金刚石,表面非常光滑;而600℃下薄膜主要是石墨成分,表面粗糙.沉积能量大于140eV,800℃时薄膜表面分立着高度取向的、垂直衬底表面、相互平行的开口碳管.用高分辨电子显微镜看到了石墨平面的垂直择优取向,离子的浅注入和应力是这种优先取向的主要机理. 关键词： 非晶碳 表面形貌 质量分离低能离子束     

Electron mobility limited by surface and interface roughness scattering in AlxGa1-xN/GaN quantum wells

The electron mobility limited by the interface and surface roughness scatterings of the two-dimensional electron gas in AlxGa1-xN/GaN quantum wells is studied. The newly proposed surface roughness scattering in the AlGaN/GaN quantum wells becomes effective when an electric field exists in the AlxGa1-xN barrier. For the AlGaN/GaN potential well, the ground subband energy is governed by the spontaneous and the piezoelectric polarization fields which are determined by the barrier and the well thicknesses. The thickness fluctuation of the AlGaN barrier and the GaN well due to the roughnesses cause the local fluctuation of the ground subband energy, which will reduce the 2DEG mobility.     

Plasmons in a free-standing nanorod with a two-dimensional parabolic quantum well caused by surface states

The collective charge density excitations in a free-standing nanorod with a two-dimensional parabolic quantum well are investigated within the framework of Bohm-Pine’s random-phase approximation in the two-subband model.The new simplified analytical expressions of the Coulomb interaction matrix elements and dielectric functions are derived and numerically discussed.In addition,the electron density and temperature dependences of dispersion features are also investigated.We find that in the two-dimensional parabolic quantum well,the intrasubband upper branch is coupled with the intersubband mode,which is quite different from other quasi-one-dimensional systems like a cylindrical quantum wire with an infinite rectangular potential.In addition,we also find that higher temperature results in the intersubband mode(with an energy of 12 meV(～ 3 THz)) becoming totally damped,which agrees well with the experimental results of Raman scattering in the literature.These interesting properties may provide useful references to the design of free-standing nanorod based devices.     

Spacer layer thickness fluctuation scattering in a modulation-doped AlxGa1-xAs/GaAs/AlxGa1-xAs quantum well

We theoretically study the influence of spacer layer thickness fluctuation（SLTF） on the mobility of a twodimensional electron gas（2DEG） in the modulation-doped Al x Ga 1 x As/GaAs/Al x Ga 1 x As quantum well.The dependence of the mobility limited by SLTF scattering on spacer layer thickness and donor density are obtained.The results show that SLTF scattering is an important scattering mechanism for the quantum well structure with a thick well layer.     

质量分离低能离子束沉积碳膜及离子轰击效应

用质量分离的低能离子束沉积技术得到了非晶碳薄膜,X射线衍射、Raman谱以及俄歇深度谱的线形表明,此种非晶碳膜中镶嵌着金刚石颗粒.碳离子的浅注入是该碳膜SP³形成的主要机理.从一个侧面说明了化学气相沉积法中偏压预处理增加金刚石成核的主要原因是因为离子轰击效应. 关键词： 非晶碳 离子轰击 质量分离低能离子束