Heteroepitaxial growth of GaP on silicon

Epitaxial gallium phosphide layers have been grown on silicon substrates by the metal-organic process. This process involves the reaction between trimethylgallium (CH₃)₃Ga and PH₃ and gives a high density of nucleation sites on the silicon. The influence of the substrate orientation and of the deposition temperature on the crystallinity of the layers has been studied. Best results were obtained on (001) oriented substrate at a deposition temperature of 800°C. X-ray reflection topographs of the layers have revealed the formation of cracks extending along the [110] direction, which are explained by the lattice mismatch and the difference in thermal expansion coefficients. The cracking is asymmetric with the main direction parallel to [110]. The density of cracks can be reduced by a two stage epitaxy. The electrical properties of undoped and n-type doped layers have been assessed by Hall and C(V) measurements. It shows auto-doping with silicon coming from the substrate.     

Vapour-phase epitaxial growth of ZnS on GaP

Single crystal layers of ZnS about 100 μm thick were grown epitaxially on GaP substrates in an open tube system using source ZnS powder and a flowing hydrogen atmosphere. The growth rate for different substrate temperatures increases with increasing hydrogen flow rate, but the growth rate profiles resemble each other in shape. The profile shifts towards the low temperature side as the source temperature is decreased. The (111)B substrate orientation is found to be preferable to the (111)A or the (100) with respect to surface morphology and crystal quality. X-ray diffraction investigations and luminescent properties show that the (111)B grown layers are of high quality. All ZnS layers grown on GaP substrates are craked on cooling, which may be due to the thermal expansion mismatch between the layer and the substrate. Heat-treatment of the grown layer does not reduce the resistivity, but increases the photoluminescence intensity markedly. Selective vapour-phase epitaxial growth has been successfully applied resulting in crack-free ZnS layers on GaP substrates.     

Ionized-cluster beam epitaxial growth of GaP films on GaP and Si substrates

Epitaxial films of GaP on GaP and Si substrates are grown by the Ionized-Cluster Beam Technology. The doping of Zn and N during the growth of the film are also discussed. A p-type epitaxial film doped by Zn and N shows an absorption spectrum similar to that of a direct transition type semiconductor. P-n junction LEDs are fabricated by depositing p-type GaP on n-type substrate. The luminescence from the device was observed.     

Annealing of electron irradiated GaP studied by positron lifetime technique

GaP single crystals were irradiated by 3 MeV electrons at 20 K to a dose of 4 × 10¹⁸ e/cm². An isochronal annealing in temperature region 77 ÷ 650 K followed the irradiation. Positron lifetime measurement indicated the presence of irradiation-induced vacancies in Ga sublattice. The vacancies disappeared at two stages observed at temperatures 200 ÷ 300 K and 450 ÷ 550 K.     

Heteroepitaxial growth of single crystal films of YIG on GdGaG substrates by hydrothermal synthesis

Heteroepitaxial growth of thin single-crystalline YIG films has been performed by hydrothermal synthesis using GdGaG single crystals as seed plates. Several solvant solutions and varied nutrient materials were tested. The best results were obtained in reacting FeNaO₂ and Y(OH)₃ at 500 °C and 1 kbar with 30° temperature gradient and 5 to 20% baffle opening. Good quality films were obtained particularly for seeds in (211) and (110) orientations. When the films were no more than 30 μm thick, they were transparent with a green color. Under polarized light, some films show very regular band shaped domains.     

Heteroepitaxial growth of Cu2O thin film on ZnO by metal organic chemical vapor deposition

Cuprous oxide (Cu₂O) thin films were grown epitaxially on c-axis-oriented polycrystalline zinc oxide (ZnO) thin films by low-pressure metal organic chemical vapor deposition (MOCVD) from Copper(II) hexafluoroacetylacetonate [Cu(C₅HF₆O₂)₂] at various substrate temperatures, between 250 and 400 °C, and pressures, between 0.6 and 2.1 Torr. Polycrystalline thin films of Cu₂O grow as single phase with [1 1 0] axis aligned perpendicular to the ZnO surface and with in-plane rotational alignment due to (2 2 0)_Cu2O(0 0 0 2)_ZnO; [0 0 1]_Cu2O[1 2¯ 1 0]_ZnO epitaxy. The resulting interface is rectifying and may be suitable for oxide-based p–n junction solar cells or diodes.     

The heteroepitaxial growth of vacuum-deposited GaP thin films on Si substrates

Heteroepitaxial GaP thin films were grown on (100) and (111)Si substrates by vacuum evaporation of the compound GaP and their structural characteristics were compared with homoepitaxial GaP films grown by the same technique on (100)GaP substrates. Nearly monocrystalline GaP thin films were deposited reproducibly on (100)Si substrates at the optimum substrate temperature of about 680–700°C and the deposition rate of 0.1 nms⁻¹. The structure of such films was comparable in quality to homoepitaxial GaP/GaP films. No monocrystalline films could be deposited on (111)Si substrates.     

Study of radiation damage on proton-bombarded GaP by PIXE

On GaP single crystals bombarded with 0.3 MeV and 1.0 MeV protons the fluence and depth dependences of radiation damage are studied by means of particle induced X-ray emission spectrometry under chaneling conditions (PIXE-C) and the Rutherford backscattering/channeling technique (RBS-C). It is demonstrated that PIXE-C is suitable to study depth profiles of damage density by the combination with the bevelling technique.     

硅基片上异质外延SiC的机理研究

本文利用低压高温MOCVD系统,成功地在Si(111)基片上外延出了具有高质量的SiC薄膜,并对其反应机理做了一些初步的研究.大部分观点认为,SiC/Si的异质外延,其最初的状态应该为Si衬底中Si的扩散.但是,本文通过在不同流量比的条件下,SiC薄膜在Si基片以及Al2O3基片上外延的比较,发现在SiC/Si的异质外延过程中起重大作用的并非Si衬底中Si的扩散,而是很大程度上作用于C向Si衬底的扩散.同时,还发现反应速率的快慢受SiH4流量所限制.当SiH4流量增加时,反应速率会明显加快,但是结晶质量会相对变差.     

Studies on the vapour growth of ZnS,ZnSe and ZnTe single crystals

Large, highly perfect single crystals (up to 10 × 10 × 5 mm³) of ZnS, ZnSe and ZnTe have been grown from the vapour phase by dissociative sublimation and chemical transport with iodine. Good quality crystals were obtained when the growth rate was limited by diffusion of the vapours rather than by thermal convection or by reaction rates at the charge and or the growing surface. The presence of an inert gas and defined iodine concentrations increase the growth stability, especially for charges with slight deviations from stoichiometry. Electronmicrographs, X-ray topographs and etching experiments revealed low dislocation densities and relatively large inclusion-free regions.     

The epitaxial growth of thick smooth films of ZnS on GaAs

The growth of smooth thick (80 μm) films of highly-ordered ZnS on GaAs substrates [oriented near the (100)] by open tube vapour transport in H₂:HCl gas flow has been investigated. We have found the surface features of the layers to be similar to those associated with GaAs epitaxy, particularly the “sand-dune” type of hillock. To obtain smooth layers, the substrates must be off the (100) plane, and precleaned in HCl acid. The most critical factor during growth was the HCl transport gas concentration (1.2-1.4%). We have investigated the influence of growth parameters on surface quality and Si contamination. The Si concentration in the films was found to be approximately directly proportional to the growth rate of the layers.     

GaP:Mg layers grown on GaN by MOCVD

We have investigated the growth of magnesium-doped GaP (GaP:Mg) layers on GaN by metalorganic chemical vapor deposition. The hole carrier concentration increased linearly from 0.8×10¹⁸ to 4.2×10¹⁸ cm⁻³ as the Bis(cyclopentadienyl) magnesium (Cp₂Mg) mole flow rate increased from 1.2×10⁻⁷ to 3.6×10⁻⁷ mol/min. However, the hole carrier concentration decreased when the CP₂Mg mole flow rate was further increased. The double crystal X-ray diffraction (DCXRD) rocking curves showed that the GaP:Mg layers were single crystalline at low CP₂Mg molar flow. However, the GaP:Mg layers became polycrystalline if the CP₂Mg molar flow was too high. The decrease in hole carrier concentration at high CP₂Mg molar flow was due to crystal quality deterioration of the GaP layer, which also resulted in the low hole mobility of the GaP:Mg layer.     

Heat and mass transfer problems in solution growth of GaP crystals by the travelling solvent method (TSM)

The influence of the natural convection on the heat and mass transfer process during growth of GaP crystals from the solution is considered. The two-dimensional quasi-stationary thermodiffusive hydrodynamic problem for the GaP growth system by travelling solvent method (TSM), as a model, has been solved. Computation is given for the temperature and concentration field distribution in the solution. The picture of vortex configuration for different lengths of the liquid zone, the shape of the growing and dissolving interfaces and also the boundary layers thickness are obtained. The experimental dependence of the growth rate on the convection intensity observed mostly confirmed the calculation results.     

Shaped crystal growth of PbTe by the open tube technique

The possibility of growing shaped A^IVB^VI crystals from the vapour phase by the open tube technique was investigated on PbTe. The thermodynamic conditions to reproducible prepare several habits of PbTe crystals — whiskers, tetrahedral prisms and cubes, platelets (a), dendrites, cubic and octahedral skeletons (b) as well as their properties were examined. The crystalline habits (a) are characterized by perfectly mirror-like (100) surfaces and low dislocation densities. The type and concentration of charge carriers are mainly determined by the vapour composition within the crystallization zone and very from n = 3 × 10¹⁷ to p = 1 × 10¹⁹cm⁻³. These properties are the reason of the interest in shaped PbTe crystals for the aim of IR optoelectronic devices.     

Study of the structural and photoluminescence properties of CdTe polycrystalline films deposited by close-spaced vacuum sublimation

The polycrystalline CdTe films were deposited by the close-spaced vacuum evaporation at the different substrate temperatures (150–550 °C). The X-ray diffraction measurements of structural and substructural properties of these films were carried out to study their phase composition and texture. The films’ parameters such as the coherent scattering domain size, microdeformation level and mean density of dislocations were determined based on the broadening of diffraction peaks. In this case the Hall and three-fold convolution approximations were used. Surface morphology, grain size and growth mechanism of the films were determined by the scanning electron microscopy. The low temperature photoluminescence measurements allowed us to establish the correlation between the point and extended defect structure on the one hand and the growth conditions on the other. As a result, the growth conditions of CdTe polycrystalline films with fairly good crystal and optical quality were determined.     

氮化物宽禁带半导体的MOCVD大失配异质外延

以氮化镓(GaN)、AlN(氮化铝)为代表的Ⅲ族氮化物宽禁带半导体是研制短波长光电子器件和高频、高功率电子器件的核心材料体系。由于缺少高质量、低成本的同质GaN和AlN衬底,氮化物半导体主要通过异质外延,特别是大失配异质外延来制备。由此导致的高缺陷密度、残余应力成为当前深紫外发光器件、功率电子器件等氮化物半导体器件发展的主要瓶颈,严重影响了材料和器件性能的提升。本文简要介绍了氮化物半导体金属有机化学气相沉积(MOCVD)大失配异质外延的发展历史,重点介绍了北京大学在蓝宝石衬底上AlN、高Al组分AlGaN的MOCVD外延生长和p型掺杂、Si衬底上GaN薄膜及其异质结构的外延生长和缺陷控制等方面的主要研究进展。最后对Ⅲ族氮化物宽禁带半导体MOCVD大失配异质外延的未来发展做了简要展望。     

反应烧结碳材料表面异质外延生长SiO2晶体的研究

利用高温反应烧结在不同结构碳材料表面热蒸发进行二氧化硅(SiO2)晶体的外延生长.采用X-射线衍射仪(XRD)、扫描电镜(SEM)和电子能谱仪(EDS)分析和研究了碳材料表面生成物的物相组成与显微形貌,探讨了SiO2晶体的外延生长机理.研究结果表明,不同结构碳材料表面能外延生长SiO2晶体,但形态不同.在碳纤维表面形成颗粒和短晶须状SiO2晶体,在石墨片上形成凸起团聚状SiO2晶体,而在金刚石表面首先形成了Si-O涂层,然后在Si-O涂层上生长棒状SiO2体.碳材料外延生长SiO2晶体是首先通过热蒸发法使Si沉积到碳材料表面,然后Si与体系中的O反应形成SiO2晶核,在不同结构碳材料表面生长SiO2晶体.     

The Behaviour of Zinc in GaP Synthesis by the SSD Technique

In this paper the principle of GaP synthesis by the SSD technique is described followed by a discussion of the results obtained in studying the transfer of an impurity such as the highly volatile zinc from the phosphorus source or gallium melt into GaP crystals. The radionuclide Zn⁶⁵ was used as a tracer to determine the concentrations of zinc in the phases involved in the process of synthesis. The results of these studies are compared with calculated values.     

Heteroepitaxial growth of InN layers on (1 1 1) silicon substrates

Indium nitride (InN) layers were grown on (1 1 1) silicon substrates by reactive magnetron sputtering using an indium target. Atomic force microscope, X-ray diffraction, and Raman spectroscopy analysis revealed that highly c-axis preferred wurtzite InN layers with very smooth surface can be obtained on (1 1 1) silicon substrates at a substrate temperature as low as 100 °C. The results indicate that the reactive sputtering is a promising growth technique for obtaining InN layers on silicon substrates at low substrate temperature with low cost and good compatibility with microelectronic silicon-based devices.