The morphology of CdTe deposited by organometallic vapor phase epitaxy: The effect of substrate misorientation

Substrate misorientation and growth temperature influence the morphology of CdTe epilayers grown by organometallic vapor phase homoepitaxy. These effects were investigated by using CdTe{100} and CdTe{100} misoriented by 2, 4, 6, and 8° toward 〈111〉_Te as substrates for growth in the temperature range from 337 to 425°C. Low angle pyramidal facets appeared on films grown on the CdTe(100) surface. The number density of these pyramidal facets decreased to zero as the substrate misorientation angle increased to 4°. At higher misorientation angles, low angle protrusions, resembling fish scales, appeared on the surface. When the temperature was increased, facet size decreased but facet density increased. The film morphology at the high misorientations, however, improved remarkably with increasing temperature. Cross-sectional transmission electron microscopy provided evidence that both the faceted CdTe films and films with a mirror-like finish were epitaxial single crystals with no planar defects. Schwoebel barriers are suggested as the reason for the faceting of the surface grown on CdTe{100}.     

C-H体系CVD金刚石薄膜取向生长的热力学分析

化学气相淀积金刚石薄膜过程中 ,CH3 和C2 H2 是金刚石生长的主要前驱基团。C2 H2 与CH3 浓度比 ( [C2 H2 ]/[CH3 ])的变化将影响金刚石薄膜的生长取向。用非平衡热力学耦合模型计算了C H体系CVD金刚石薄膜生长过程中C2 H2 浓度和CH3浓度随淀积条件的变化 ,并进一步获得了 [C2 H2 ]/[CH3 ]随衬底温度和CH4浓度的变化关系 ,从理论上探讨了金刚石薄膜 ( 1 1 1 )面和 ( 1 0 0 )面取向生长与淀积条件的关系。在衬底温度和CH4浓度由低到高的变化过程中 ,[C2 H2 ]/[CH3 ]逐渐升高 ,导致金刚石薄膜的形貌从 ( 1 1 1 )晶面转为 ( 1 0 0 )晶面。     

Structural characterization of low temperature Epi-silicon grown on {100} and {111} Si substrates using ultrahigh resolution cross-sectional TEM

Low defect-density epitaxial silicon was grown at 550°C, but it became polysilicon or amorphous silicon when the substrate was submitted to bombardment of ECR argon plasma prior to growth. Through carefully characterizing the interface and structure of low temperature epitaxial silicon films using ultrahigh resolution cross-sectional transmission electron microscopy (UHRXTEM), defects were found to have different features in silicon epitaxial layers grown on {100} and {111} silicon substrates. Twinning was more likely to generate in the epitaxial layer grown on the {111} silicon substrate while stacking faults had priority in forming in the epitaxial layer grown on the {100} substrate. The probable causes of different defect formation mechanisms were analyzed and discussed with the help of UHRXTEM lattice images. The atom model of the twin boundary in the epitaxial silicon film was analyzed in detail.     

Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning Mechanisms

Three groups of free‐standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high‐resolution electron back‐scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp³ hybridization of the bond in the CH₄ molecule that is used as the deposition medium.     

Pore Sealing on Si(001) and Si(111) in Homoepitaxy and Annealing: A Monte Carlo Simulation

A Monte Carlo simulation is reported of (i) the homoepitaxial growth of a continuous film on porous Si(111) and Si(001) surfaces and (ii) high-temperature annealing of a porous-silicon substrate. The simulation is based on a 3D model for diamond-type crystals. It is shown that homoepitaxy produces a smooth film on a (111) surface, whereas the film on a (001) surface shows {111} tetrahedral pits. It is found that the minimum deposited dose required for pore sealing is much lower for a (111) surface; this is true of all temperatures, deposition rates, and porosities considered. The difference in surface morphology between the two films is attributed to the influence of surface orientation on adatom migration. The variation is examined of pore penetration depth with respect to epitaxy conditions and porosity. Structural changes under annealing are investigated in the Si(001) case.     

Cl2 chemical dry etching of GaAs under high vacuum conditions—Crystallographic etching and its mechanism

Cl₂ chemical dry etching for GaAs substrates of {111}A, {111}B, {110} and {100} orientations was accomplished under high vacuum conditions. The etch rate for different substrate orientations was {111}B > {110} = {100} > {111}A for temperatures below 450° C, and was nearly equal for temperatures above 450° C. For {111}B, {110} and {100} substrates, the etch rate depends strongly on the substrate temperature above 450° C and below 150° C. Two activation energies for etching (10.0 kcal/mol below 150° C and 16.0 kcal/mol above 450° C) were obtained. Between 150 and 450° C, the etch rate depends weakly on the substrate temperature. However, for {111}A substrate, the etch rate increased monotonically with increasing substrate temperature above 300° C. The activation energy corresponds to that for the other substrates above 450° C. These results are caused by the surface chemical reaction of GaAs/Cl₂. By using these etching properties, a vertical side wall was fabricated without ion bombardment.     

HWE生长条件对CdTe/Si薄膜结构特性的影响

研究了热壁外延(HWE)生长条件对Si(100)衬底上沉积外延的多晶CdTe薄膜的晶粒尺寸和取向的影响.用SEM和XRD技术分析了不同外延时间、不同衬底温度及不同源温下外延膜的表面形貌和结构特征.SEM发现随着外延时间的增加或衬底温度的提高,晶粒尺寸明显增大;XRD显示所有的外延薄膜均为面心立方结构,并高度显示优势取向(111),且随着衬底温度或薄膜厚度的增加,(111)峰的衍射强度增加,显示薄膜的择优取向更好.其原因是面心立方结构中,(111)表面具有的表面自由能最低.通过对不同外延时间下薄膜厚度的测试发现,薄膜具有加速生长趋势.衬底温度及源温对外延层厚度均有较大的影响.     

The effect of substrate tilt on MOCVD growth of {100}CdTe on {100}GaAs

Epitaxial layers of CdTe were grown by metalorganic chemical vapor deposition on surfaces of single crystal, {100} GaAs which had been ground, polished, and etched to a spherically shaped done. This dome-shaped surface allowed the morphological and structural properties of the epitaxial CdTe layers to be determined for all 360° of azimuth and up to 15° of polar angle from the [100] axis within a single growth experiment. At two growth temperatures, approximately 275 and 375°C, the results show distinct twofold rotational symmetry in both morphology and crystal perfection as determined by x-ray rocking curve measurement. Surface morphology is superior at azimuths near tilts toward the <111>A pole. Four-sided pyramidal hillocks appear at other azimuths and at 0° tilt; the symmetry of the hillocks diminishes as the tilt increases. The orientations for growth which simultaneously minimize the surface defects and rocking curve full-width half-maximum appear to be at locations on the surface where the surface normal is tilted 3–4° toward the <111>A or <111>B, depending on the temperature regime chosen. Epitaxial layers grown on planar wafers of {100}GaAs tilted toward <111>Ga and <111>As show surface morphology essentially identical to the dome at these orientations. The surface morphology of CdTe growth on GaAs/Si wafers suggests that these layers are tilted toward the <111>B.     

Metalorganic Chemical Vapor Deposition of CdTe(133) Epilayers on Si(211) Substrates

Single-crystalline CdTe(133) films have been grown by metalorganic chemical vapor deposition on Si(211) substrates. We studied the effect of various growth parameters on the surface morphology and structural quality of CdTe films. Proper oxide removal from the Si substrate is considered to be the principal factor that influences both the morphology and epitaxial quality of the CdTe films. In order to obtain single-crystalline CdTe(133) films, a two-stage growth method was used, i.e., a low-temperature buffer layer step and a high- temperature growth step. Even when the low-temperature buffer layer shows polycrystalline structure, the overgrown layer shows single-crystalline structure. During the subsequent high-temperature growth, two-dimensional crystallites grow faster than other, randomly distributed crystallites in the buffer layer. This is because the capturing of adatoms by steps occurs more easily due to increased adatom mobility. From the viewpoint of crystallographic orientation, it is assumed that the surface structure of Si(211) consists of (111) terrace and (100) step planes with an interplanar angle of 54.8°. This surface structure may provide many preferable nucleation sites for adatoms compared with nominally flat Si(100) or (111) surfaces. The surface morphology of the resulting films shows macroscopic rectangular-shaped terrace—step structures that are considered to be a (111) terrace with two {112} step planes directed toward 〈110〉.     

Morphological evolution,Raman and photoluminescence spectra in optically transparent cubic silicon carbide

Optically transparent cubic SiC crystals were grown via atmospheric-pressure chemical vapour deposition (APCVD) on graphite substrates from methyltrichlorosilane (MTS) in hydrogen in a cold-wall RF induction furnace at temperatures from 1500 to 2000°C. The morphology of the crystals was correlated to substrate temperature, H₂/MTS ratio and hydrogen flow. Low-temperature photoluminescence (PL) spectra exhibited a zero-phonon line (2.3787 eV) attributable to an exciton bound to a neutral nitrogen donor, in addition to TA, LA, TO, and LO phonon replicas. The observed broadening and splitting of the PL spectral lines were associated with the morphological habit and internal strain of individual crystallites. Above about 1600°C preferential 〈110〉 growth directions were identified for the majority of the crystals. At intermediate deposition temperatures (1600–1700°C) the dominant morphology consisted of yellow prismatic crystals heavily twinned along {111} and {111¯}. At temperatures of about 1750°C hexagonally shaped {111}-oriented 3C-SiC platelets were formed with alternating {001}/{101} edges. A layer-by-layer growth model was used to rationalise the transition in preferred growth direction from 〈111〉 to 〈101〉 with increasing substrate temperature. © 1997 John Wiley & Sons, Ltd.     

Selective etch-back and growth of InGaAs ON (100) Fe:lnP by electroepitaxy

Selective etch-back prior to growth of InGaAs islands on SiO₂-masked (100)Fe-doped InP substrates was performed by electroepitaxy. The etch-back of the substrate and the growth of the layer was done at a constant furnace temperature of 640° C by passing a direct electric current from the melt to the substrate for etch-back and from the substrate to the melt for growth. The current density used was 1 to 20 A/cm² for a period from 15 to 60 min. The isolated InP regions were of various sizes (40 × 1000μm to 3000 × 3000μm), and different geometries (narrow and wide strips, square, circular). A uniform etch-back and uniform growth with excellent surface morphology was obtained on strips as wide as 200μm and on circles withd < 500μm. For islands with wider geometry, growth as well as etch-back were uniform up to 100–200μm from the periphery with excellent surface morphology. The etch-back and growth profiles are trapezoid-shaped and are not influenced by the difference in chemical activity between crystalline planes. The orientation dependence of the etch rate was {110} > {100} > {011} > {111} B > {111} A.     

喷射CVD法制备金刚石厚膜及其内应力分析

采用直流电弧等离子体喷射CVD法制备出金刚石薄膜,利用扫描电子显微镜(SEM)、Raman光谱及X射线衍射(XRD)等研究基底温度对金刚石厚膜生长特性及内应力的影响。结果表明:950℃基底温度生长的金刚石厚膜结晶性能较好,纯度较高;而850℃和1050℃生长的金刚石厚膜表面呈现大量的孪晶缺陷,结晶度较低,同时出现较多的非金刚石碳,纯度较低。随着基底温度的增加,(111)晶面和(311)晶面的衍射峰强度逐渐增强,(220)晶面的衍射峰强度逐渐降低。850℃和950℃基底温度生长的金刚石厚膜的宏观应力和微观应力都呈现出拉应力,1050℃基底温度生长的金刚石厚膜的宏观应力和微观应力都呈现出压应力。     

Growth and characterization of diamond films on nondiamondsubstrates for electronic applications

Recent advances in the chemical vapor deposition (CVD) and characterization of diamond films on nondiamond substrates are reviewed. Major growth techniques, including hot filament CVD; microwave, RF, or DC plasma enhanced CVD; and combustion flame growth; as well as a number of hybrid and novel approaches, are described and analyzed. Results from the major categories of diamond film characterization, including diamond phase identification, nucleation and interfacial phenomena, morphology, and defects, as well as their correlations with electrical properties, are examined and discussed. Although most of the information presented is equally applicable to protective and wear-resistant coating application, emphasis is placed in the areas most pertinent to microelectronics     

HFCVD金刚石薄膜的热场模拟及实验

基体温度是影响金刚石薄膜生长质量的重要因素之一.基于有限元分析法,通过AN-SYS CFX软件对基体温度场进行模拟仿真,得到基体表面温度场的分布,并分别讨论了热丝-基体距离、热丝间距、水冷系数等参数对系统温度场均匀性和一致性的影响.经仿真优化后得到的参数值分别为热丝-基体距离10 mm、热丝间距15 mm、水冷系数1 000 W/(m2·K).在此优化工艺的基础上进行热丝化学气相沉积(HFCVD)金刚石薄膜的实验,并采用扫描电子显微镜(SEM)和X射线衍射仪(XRD)对金刚石薄膜表面特征进行检测.结果表明:利用仿真优化后的薄膜生长参数,可以在金刚石薄膜生长区域得到比较均匀的多晶金刚石薄膜.     

基片预处理工艺对CVD金刚石成核行为的影响

本文采用微波等离子体辅助化学气相沉积工艺,对不同预处理的(100)单晶硅基片上金刚石的成核行为进行了初步研究,并利用定量金相及扫描电子显微镜分析了金刚石的成核速率及晶体特征。由此提出了用0.1μm超细金刚石粉对基片的研磨工艺。该工艺可有效提高金刚石成核率,从而有助于获得晶粒细小均匀,表面粗糙度低的金刚石薄膜。采用C60涂复并结合研磨工艺,使成核率获得了进一步提高。     

Microstructural Characterization of HgCdSe Grown by Molecular Beam Epitaxy on ZnTe/Si(112) and GaSb(112) Substrates

Transmission electron microscopy and small-probe microanalysis have been used to investigate the microstructure of HgCdSe thin films grown by molecular beam epitaxy on ZnTe/Si(112) and GaSb(112) substrates. The quality of the HgCdSe material was dependent on the growth temperature and materials flux, independent of the substrate. Samples grown at 100°C were generally of high quality, while those grown at 140°C had {111}-type stacking defects and increased dislocation densities. Improved preparation of the GaSb buffer layer should be developed for future HgCdSe growth on GaSb(112) substrates.     

Growth of diamond films on si(100) with and without boron nitride buffer layer

Diamond films were grown on Si(100) and boron nitride deposited Si(100) substrates using hot filament chemical vapor deposition (HFCVD) technique. Microstructure and morphology of diamond films have been investigated systematically as a function of CH₄ and H₂ ratio and the ambient pressure. The deposited films were characterized by employing techniques such as scanning electron microscopy (SEM) and laser Raman spectroscopy. The average size and growth rate of diamond particles were found to increase with the CH₄ to H₂ ratio and decrease with the ambient pressure. Maximum growth rate of synthetic diamond deposited on Si(100) was found to be &#x223C;3.5 &#x00B5;m/hr for the film deposited at 20 Torr with CH₄:H₂ &#x223C; 1.5:100 (substrate temperature &#x223C;850&#x00B0;C). In most of these depositions, the morphology of the diamond crystals was cubic with significant secondary nucleation at higher methane concentrations and ambient pressure. The diamond film deposited on Si(100) with BN buffer layer shows an improvement in growth rate and the coverage, and the secondary nucleation was found to be substantially reduced, resulting in relatively smooth morphology. MicroRaman investigations show less amorphous graphite formation and better structural quality of diamond film than the one deposited without the BN buffer layer. On leave from Department of Physics University of Poona, Pune-411007 INDIA     

Full-Wafer Characterization of AlGaN/GaN HEMTs on Free-Standing CVD Diamond Substrates

We report on electrical characterization and uniformity measurements of the first conventionally processed AlGaN/GaN high electron mobility transistors (HEMTs) on free-standing chemical-vapor-deposited (CVD) diamond substrate wafers. DC and RF device performance is reported on HEMTs fabricated on $sim!!hbox{130-}muhbox{m}$-thick and 30-mm round CVD diamond substrates without mechanical carrying wafers. A measured $f_{T} cdot L_{G}$ product of 12.5 $hbox{GHz} cdot muhbox{m}$ is the best reported data for all GaN-on-diamond technology. X-band power performance of AlGaN/GaN HEMTs on diamond is reported to be 2.08 W/mm and 44.1% power added efficiency. This letter demonstrates the potential for GaN HEMTs to be fabricated on CVD diamond substrates utilizing contact lithography process techniques. Further optimization of the epitaxy and diamond substrate attachment process could provide for improvements in thermal spreading while preserving the electrical properties.      

LSAT(111)衬底上ZnO单晶薄膜的分子束外延生长

利用射频等离子体辅助分子束外延技术,在LSAT(111)衬底上制备高质量ZnO单晶薄膜.研究了衬底表面预处理及生长温度对ZnO外延膜的生长过程、外延取向关系以及表面形貌的影响.发现在较低温度下生长ZnO时,薄膜中容易形成30. 旋转畴,而在较高温度下,可完全消除薄膜中的旋转畴,得到具有单一畴的ZnO单晶薄膜，讨论了旋转畴的起源以及生长温度对于消除旋转畴的作用.锐利的3×3 RHEED图像验证了ZnO薄膜具有O极性     

金刚石/硅复合膜的导热特性研究

用金刚石粉,用不同时间在两片镜面抛光的(111)硅基片上分别打磨.两片硅基片打磨后都仍保持镜面特征.采用微波等离子体化学气相沉积系统,利用氢气、甲烷和氧气为前驱气体,在同样参数条件下,在基片上制备了直径5 cm的金刚石薄膜.用扫描电镜和X射线衍射分析两片薄膜结构.分析结果表明其表面形貌基本相同都为(111)择优取向的金刚石薄膜;但X射线衍射分析表明打磨时间较长的薄膜中含有一定量在非晶成分.用热导测试仪测试两薄膜和硅基片的热导率约为:241.7 W/mK,192.9 W/mK和169.3 W/mK.结合扫描电镜和X射线衍射分析结果我们讨论了基底处理对金刚石/硅复合膜的导热特性的影响.