低温下应变外延层的单层生长

用接触式原子力显微镜来观察 4 6 0℃低温下生长的 In0 .35Ga0 .6 5As/ Ga As外延层形貌 .实验发现 ,这种 4 6 0℃低温生长材料的失配外延层既不是层状的 Fvd M生长模式也不是岛状的 SK自组织生长模式 ,而是由原子单层构成的梯田状大岛 .原子力显微镜测试表明台阶的厚度为 0 .2 8nm,约为一个原子单层 ,这种介于层状和岛状生长之间的模式有助于了解失配异质外延的生长过程     

利用全固态分子束外延方法在Ge(100)衬底上异质外延GaAs薄膜及相关特性表征

利用全固态分子束外延(MBE)方法在Ge(100)衬底上异质外延GaAs薄膜,并通过高能电子衍射(RHEED)、高分辨X射线衍射(XRD),原子力显微镜等手段研究了不同生长参数对外延层的影响.RHEED显示在较高的生长温度或较低的生长速率下,低温GaAs成核层呈现层状生长模式.同时降低生长温度和生长速率会使GaAs薄膜的XRD摇摆曲线半高宽(FWHM)减小,并降低外延层表面的粗糙度,这主要是由于衬底和外延薄膜之间的晶格失配度减小的结果.     

蓝宝石上横向外延GaN薄膜

在蓝宝石衬底上利用金属有机物气相外延(MOCVD)方法对横向外延(ELO)GaN薄膜的生长条件进行了研究.在蓝宝石衬底上利用化学腐蚀的方法刻饰出图案,再沉积低温GaN缓冲层作为外延层的子晶层,以降低外延层与衬底的晶格失配与热失配,制备出低位错密度的GaN外延层.分别利用X射线衍射、原子力显微镜及湿法腐蚀对外延层进行检测.     

蓝宝石上横向外延GaN薄膜

在蓝宝石衬底上利用金属有机物气相外延(MOCVD)方法对横向外延(ELO)GaN薄膜的生长条件进行了研究.在蓝宝石衬底上利用化学腐蚀的方法刻饰出图案,再沉积低温GaN缓冲层作为外延层的子晶层,以降低外延层与衬底的晶格失配与热失配,制备出低位错密度的GaN外延层.分别利用X射线衍射、原子力显微镜及湿法腐蚀对外延层进行检测.     

硅衬底上锗外延层的生长北大核心CSCD

利用超高真空化学气相沉积系统,基于低温Ge缓冲层技术,研究了Si衬底上高质量Ge外延层的生长。结果表明,低温Ge缓冲层的表面起伏较大,降低生长温度并不能抑制三维岛状生长。然而,低温Ge缓冲层的压应变几乎被完全弛豫,应变弛豫度达到90%以上。在90 nm低温Ge缓冲层上生长的210 nm高温Ge外延层,表面粗糙度仅为1.2 nm。Ge外延层X射线双晶衍射峰的峰形对称,峰值半高宽约为460 arcsec,无明显的Si-Ge互扩散。湿法化学腐蚀部份Ge外延层,测量位错密度约为5×10~5cm^(-2)。     

原子氢辅助分子束外延生长台阶状表面形貌的研究

研究了分子束外延中引入原子氢后,原子氢对外延层表面形貌特征形成的诱导作用.原子力显微镜(AFM)测试表明,在(311)A GaAs表面,原子氢导致了台阶状形貌的形成,在这种台阶状表面进一步生长了InAs量子点,测试结果表明其位置分布的有序化受到台阶高度和台阶周期的制约.这为实现量子点结构的有序化控制生长提供了一定的实验参考.     

原子氢辅助分子束外延生长台阶状表面形貌的研究

研究了分子束外延中引入原子氢后 ,原子氢对外延层表面形貌特征形成的诱导作用 .原子力显微镜 (AFM)测试表明 ,在 (311) A Ga As表面 ,原子氢导致了台阶状形貌的形成 ,在这种台阶状表面进一步生长了 In As量子点 ,测试结果表明其位置分布的有序化受到台阶高度和台阶周期的制约 .这为实现量子点结构的有序化控制生长提供了一定的实验参考 .     

采用低温AlN插入层在氢化物气相外延中生长GaN膜

采用低温AlN插入层在氢化物气相外延(HVPE)设备中生长出高质量GaN膜。X射线衍射(XRD)测量发现,低温AlN插入层有助于提高GaN膜的结晶质量。低温(10K)光致发光(PL)谱测量表明,低温AlN插入层有助于释放GaN膜外延生长的应力。原子力显微镜(AFM)测量显示,GaN膜具有非常光滑的表面形貌,并估算出其位错密度约为3.3×108cm-2。     

少层氮化硼的生长机理及技术研究北大核心

采用MOCVD技术在50.8 mm(2英寸)蓝宝石衬底上开展氮化硼(BN)材料的外延生长研究。基于Ⅴ/Ⅲ族源的同时输运工艺,探究了无序岛状、生长自终止及二维层状等三种BN生长模式的外延机理,并实现了5-6层原子厚的二维BN材料的制备。同时,提出了一种Ⅴ/Ⅲ族源的同时输运及分时输运相结合的外延生长工艺,显著提升了二维BN材料质量,其中1μm×1μm表面粗糙度Ra为0.10 nm,光学带隙宽度为5.77 eV,拉曼E2g模式的半高宽为60.7 cm^(-1)。     

ALE法对InSb/GaAs异质薄膜电学性能的改进

以GaAs(100)为衬底,采用原子层外延(ALE)的方法在GaAs缓冲层和常规InSb外延层间引入85个周期约30 nm的InSb低温缓冲层,以快速降低InSb和GaAs界面间较大的晶格失配(14.6%)对外延层质量造成的不利影响,从而改进异质外延薄膜的电学性能。实验结果显示,ALE低温缓冲层能较快地释放晶格失配应力,降低位错密度。室温和77 K的Hall测试显示,引入低温ALE缓冲层生长的InSb/GaAs异质外延薄膜,其InSb外延层本征载流子浓度和迁移率等电学性能较常规的方法有着较大的改进。     

生长功率对HgCdTe薄膜微观结构以及表面形貌影响

实验采用射频磁控溅射生长了HgCdTe薄膜,并利用台阶仪、XRD、原子力显微镜等现代分析手段对HgCdTe薄膜的生长速率、物相、表面形貌进行了研究。实验结果表明,随着溅射功率增大,其生长速率成线性增大,当溅射功率低于30w时,薄膜XRD衍射图谱上没有出现任何特征衍射峰,只是在2θ=23°附近出现衍射波包,材料具有明显的非晶态特征,当溅射功率高于30w时,XRD表现为多晶结构;AFM和SEM分析表明生长速率对HgCdTe薄膜表面粗糙度、形貌、形成机理等有直接影响,随着生长速率提高,薄膜表面粗糙度逐渐增大,且薄膜逐渐形成“迷津”结构。     

Effect of power variation on microstructure and surface morphology of HgCdTe films deposited by RF magnetron sputtering

Mercury cadmium telluride films were grown by the RF magnetron sputtering technique at different sputtering powers.In experiment,X-ray diffraction (XRD) and atomic force microscopy (AFM) have been used to characterize the microstructure of HgCdTe films.The experimental results showed that when the growth power increased,the growth rate of HgCdTe films increased; when the growth power was less than 30 W,the HgCdTe film deposited by RF magnetron sputtering was amorphous; when the growth power was more than 30 W,the films exhibited polycrystalline structure.Films deposited at different growth rates were found to have characteristically different formations and surface morphologies; as observed through AFM,the surface morphology is composed of longitudinal islands forming a maze-like pattern in the high deposition rate.AFM analysis also illustrated that a significant reduction in the areal density of large islands and characteristically smoother films was achieved using a low deposition rate.     

Epitaxial growth of ZnO on GaN/sapphire substrate by radio-frequency magnetron sputtering

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization.     

Initial stages of InP/GaP (100) and (111)A,B grown by metal organic chemical vapor deposition

The initial stages of the three-dimensional metal organic vapor phase epitaxy growth of InP/GaP (100) and (111)_A,B were studied by atomic force microscopy (AFM) and Rutherford back scattering (RBS). We have shown that the heteroepitaxial growth takes place under Stranski–Krastanov mode (layer by layer and dislocation free island growth). By combining RBS and AFM results, we show that the wetting layer is about 0.51 and 0.4 nm for (100) and (111)_A,B orientated substrates, respectively. The critical thickness is found to depend on the substrate orientation. However, we show by the AFM technique that the shape, the height and the size of uncapped InP/GaP self-organized nanostructures depend on the amount of InP deposited and on the substrate orientation. In particular, the structure grown on (111)_A,B substrate presents higher islands than the structure grown on (100). Therefore, the formation of nanostructures on substrates different from (100) is an interesting possibility to be investigated.     

GaAs（331）A衬底上分子束外延生长自组织InAs纳米结构形貌演化机制

采用分子束外延方法在GaAs(331)A高指数衬底上制备自对齐InAs量子线(QWR)或者三维(3D)岛状结构。InAs量子线(QWR)选择性生长在GaAs层的台阶边缘。通过原子力显微镜(AFM)仔细研究了InAs纳米微结构的表面形貌,发现不同的生长条件如衬底温度、生长速率和InAs层厚度等,对InAs表面形貌有很大的影响。低温更容易导致线状纳米微结构的形成,而高温更利于3D岛状结构形成。表面形貌的转变归结于表面能同应变能之间的竞争。     

Study of the Piezoelectric Power Generation of ZnO Nanowire Arrays Grown by Different Methods

The piezoelectric power generation from ZnO nanowire arrays grown on different substrates using different methods is investigated. ZnO nanowires were grown on n‐SiC and n‐Si substrates using both the high‐temperature vapor liquid solid (VLS) and the low‐temperature aqueous chemical growth (ACG) methods. A conductive atomic force microscope (AFM) is used in contact mode to deflect the ZnO nanowire arrays. No substrate effect was observed but the growth method, crystal quality, density, length, and diameter (aspect ratio) of the nanowires are found to affect the piezoelectric behavior. During the AFM scanning in contact mode without biasing voltage, the ZnO nanowire arrays grown by the VLS method produced higher and larger output voltage signal of 35 mV compared to those grown by the ACG method, which produce smaller output voltage signal of only 5 mV. The finite element (FE) method was used to investigate the output voltage for different aspect ratio of the ZnO nanowires. From the FE results it was found that the output voltage increases as the aspect ratio increases and starts to decreases above an aspect ratio of 80 for ZnO nanowires.     

InP外延材料的MBE生长模式

采用固态磷源分子束外延技术,在不同的生长条件下生长了InP外延材料,并用原子力显微镜对样品表面形貌进行了系统研究.实验结果表明,样品表面形貌的显著变化与生长模式发生变化有关;二维(2D)生长模式和三维(3D)生长模式之间存在转换的临界工艺条件.通过对实验数据的分析,绘制了InP外延生长模式对应工艺条件的区域分布图;在2D生长区域获得了高质量的InP/InP外延材料.     

HVPE法生长AlN薄膜材料

利用自制立式HVPE设备,在蓝宝石衬底上进行了不同载气情况下AlN的生长试验,生长温度1 000℃。在采用H2作载气情况下,由于预反应严重,没能生长出AlN薄膜,只得到一些白色AlN粉末;而在分别采用Ar和N2作载气的情况下,则成功生长出AlN薄膜,但由于生长温度低,AlN生长均为岛状生长模式。在生长速率较快时,AlN薄膜是以〈0001〉AlN为主的AlN多晶;而在较低生长速率下,得到的AlN薄膜由为〈0001〉取向的AlN岛组成。试验还发现:用Ar作载气更有利于AlN晶核的横向生长,用N2作载气则有相对高得多的AlN成核密度。     

Optical properties and structure of InAs quantum dots in near-infrared band

The InAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are studied as a function of growth temperature at a specific InAs coverage of 2.7 ML. The QDs density is significantly reduced from 8.0 × 1010 to 5.0 × 109 cm-2 as the growth temperature increases from 480℃ to 520℃, while the average QDs diameter and height becomes larger. The effects of the growth temperature on the evolution of bimodal QDs are investigated by combining atomic force microscopy (AFM) and photoluminescence (PL). Results show that the formation of the bimodal QDs depends on the growth temperature: at a growth temperature of 480℃,large QDs result from the small QDs coalition; at a growth temperature of 535℃, the indium desorption and InAs segregation result in the formation of small QDs.     

Mechanisms determining three-dimensional SiGe lsland density on Si(001)

Thin, coherently strained, films of SiGe were deposited on Si(001) in the Stranski-Krastanow (SK) growth mode to form small, faceted, dislocation-free-three-dimensional (3D) islands. The number density of these islands was determined as functions of SiGe alloy composition, growth rate, and substrate temperature during growth. From these experiments, the classical model of 3D island nucleation and growth yields an approximate activation energy for diffusion of Ge dimers on a Ge covered Si(001) surface of 0.70 eV. The dependence of the 3D-island number density on growth rate cannot be understood without modifying the classical model to account for the wetting layer present in SK systems. Heteroepitaxial strain is not included in the classical model of island nucleation and growth. A simple linear elastic model that fits the data is developed that predicts the island number density is proportional to the inverse square of the Ge mole fraction in the alloy plus a constant.