Growth of high quality InSb thin films on GaAs substrates by molecular beam epitaxy method with AlInSb/GaSb as compound buffer layers

A series of In Sb thin films were grown on Ga As substrates by molecular beam epitaxy(MBE).Ga Sb/Al In Sb is used as a compound buffer layer to release the strain caused by the lattice mismatch between the substrate and the epitaxial layer,so as to reduce the system defects.At the same time,the influence of different interface structures of Al In Sb on the surface morphology of buffer layer is explored.The propagation mechanism of defects with the growth of buffer layer is compared and analyzed.The relationship between the quality of In Sb thin films and the structure of buffer layer is summarized.Finally,the growth of high quality In Sb thin films is realized.     

Influence of MgO substrate treatment on the structure-sensitive properties of epitaxial films (by the example of iron films)

A new technology of growing thin single-crystal MgO films on the MgO crystal surface using the method of chemical transport reactions is developed. The quality of deposited sublayers is checked with the structure-sensitive properties of iron epitaxial films.     

纤锌矿GaN薄膜光学性质的研究

在测试大量纤锌矿GaN外延薄膜透射光谱基础上,通过对有代表性的四个样品的透射光谱进行拟合,获取了GaN外延薄膜的光学常量并计算了薄膜厚度.结果表明:GaN外延薄膜的折射率差异较小,但在370～800 nm波长范围内消光系数差异很大,GaN薄膜的消光系数差异在一定程度上可用以评价外延薄膜的质量.     

硅基锗薄膜的红外吸收谱和电学特性

为了解退火对硅基锗薄膜的质量、红外吸收、透射率和电学性质的影响,采用分子束外延方法用两步法在硅基上生长锗薄膜。将生长后的样品分成两部分,其中一部分进行了退火处理。对退火前后的样品用高分辨X射线双晶衍射仪测量了(400)晶面的X射线双晶衍射摇摆曲线,用傅里叶红外光谱仪测量了红外透射率和吸收谱,并用霍尔效应仪测量了退火前后样品的载流子浓度、迁移率、电阻率、电导率和霍尔系数。结果表明,退火后的薄膜质量明显提高。退火后大部分区域吸收增大,透射率明显减小,615~3 730 cm-1区间的透射率均比退火前降低了20%以上。退火后的体载流子浓度增大到退火前的23.26倍,迁移率增大到退火前的27.82倍。     

UV detectors based on epitaxial diamond films grown on single-crystal diamond substrates by vapor-phase synthesis

The prospects for use of CVD-technology for epitaxial growth of single-crystal diamond films of instrumental quality in UHF plasma for the production of optoelectronic devices are discussed. A technology for processing diamond single crystals that provides a perfect surface crystal structure with roughness less than 0.5 nm was developed. It was demonstrated that selective UV detectors based on synthetic single-crystal diamond substrates coated with single-crystal films can be produced. A criterion for selecting clean and structurally perfect single crystals of synthetic diamond was developed for the epitaxial growth technology.     

Epitaxial growth of InN on nearly lattice-matched (Mn,Zn)Fe2O4

We have grown InN films on nearly lattice-matched (Mn,Zn)Fe₂O₄ (111) substrates at low temperatures by pulsed laser deposition (PLD) and investigated their structural properties. InN films grown at substrate temperatures above 400 °C show poor crystallinity, and their in-plane epitaxial relationship is [10-10]InN//[11-2](Mn,Zn)Fe₂O₄, which means that their lattice mismatch is quite large (11%). By contrast, high quality InN films with flat surfaces can be grown at growth temperatures lower than 150 °C with the ideal in-plane epitaxial relationship of [11-20]InN//[11-2](Mn,Zn)Fe₂O₄, which produces lattice mismatches of as low as 2.0%. X-ray reflectivity measurements have revealed that the thickness of the interfacial layer between the InN and the substrates is reduced from 14 to 8.4 nm when the growth temperature is decreased from 400 °C to room temperature. This suppression of the interface reactions by reducing the growth temperature is probably responsible for the improvement in crystalline quality. These results indicate that the use of (Mn,Zn)Fe₂O₄ (111) substrates at low growth temperatures allows us to achieve nearly lattice matched epitaxial growth of InN.     

Interfacial reactions of ultrahigh vacuum deposited ytterbium thin films on silicon

Epitaxial ytterbium silicide thin films were grown on (111)Si by ultrahigh vacuum deposition and subsequent thermal annealing. The epitaxial YbSi(2-x) thin films consist of various kinds of defects such as vacancies, stacking faults, and pinholes. The vacancies were ordered so as to relax the compressive stress in Si sublattice of YbSi(2-x) thin films. The vacancy ordering structure is of an out-of-step structure with higher vacancy concentration after higher temperature annealing so that the compressive stress was further relaxed. A high density of stacking faults was present in the epitaxial YbSi(2-x) thin films. The stacking faults were annihilated by high temperature annealing. Pinholes also formed in the epitaxial YbSi(2-x) thin films and could be avoided by appropriate fabrication process. The epitaxial YbSi(2-x) thin films were thermally stable up to 1000 degrees C.     

Photoassisted chemical solution deposition method for fabricating uniformly epitaxial VO2 films

Epitaxial VO₂ films were prepared on the TiO₂ (001) substrates by the excimer-laser-assisted metal–organic deposition (ELAMOD). The quality of the epitaxial films obtained by irradiation with a KrF laser was found to be affected by the film structure obtained after preheating at 500 or 300°C. When the films containing crystal domains, which were obtained by preheating at 500°C, were irradiated with the laser at room temperature under a base pressure of 250 Pa, epitaxial and polycrystalline VO₂ phases were simultaneously formed. In contrast, when the amorphous films containing organic components, which were obtained by preheating at 300°C, were irradiated with the laser at room temperature in air, a single phase of epitaxial VO₂ was formed. By using thermal simulations, we determined that the formation of the epitaxial phase was affected both by the temperature distribution within the film during the laser irradiation and by the laser intensity at the interface between the substrate and the film. The latter factor is considered to play a role in the nucleation of crystallization, causing the epitaxial phase to form preferentially compared to the polycrystalline phase in the amorphous matrix of the films. These results indicate that the ELAMOD process is effective for the fabrication of epitaxial VO₂ films at low temperature.     

Synthesis of epitaxial silicon carbide films through the substitution of atoms in the silicon crystal lattice: A review

A review of recent advances in the field of epitaxial growth of SiC films on Si by means of a new method of epitaxial substitution of film atoms for substrate atoms has been presented. The basic statements of the theory of the new method used for synthesizing SiC on Si have been considered and extensive experimental data have been reported. The elastic energy relaxation mechanism implemented during the growth of epitaxial SiC films on Si by means of the new method of substitution of atoms has been described. This method consists in substituting a part of carbon atoms for silicon matrix atoms with the formation of silicon carbide molecules. It has been found experimentally that the substitution for matrix atoms occurs gradually without destroying the crystalline structure of the matrix. The orientation of the film is determined by the “old” crystalline structure of the initial silicon matrix rather than by the silicon substrate surface only, as is the case where conventional methods are used for growing the films. The new growth method has been compared with the classical mechanisms of thin film growth. The structure and composition of the grown SiC layers have been described in detail. A new mechanism of first-order phase transformations in solids with a chemical reaction through an intermediate state promoting the formation of a new-phase nuclei has been discussed. The mechanism providing the occurrence of a wide class of heterogeneous chemical reactions between the gas phase and a solid has been elucidated using the example of the chemical interaction of the CO gas with the single-crystal Si matrix. It has been shown that this mechanism makes it possible to grow a new type of templates, i.e., substrates with buffer transition layers for growing wide-band-gap semiconductor films on silicon. A number of heteroepitaxial films of wide-band-gap semiconductors, such as SiC, AlN, GaN, and AlGaN on silicon, whose quality is sufficient for the fabrication of a wide class of micro- and optoelectronic devices, have been grown on the SiC/Si substrate grown by solid-phase epitaxy.     

Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics

A combined experimental and computational investigation of coupling between polarization and epitaxial strain in highly polar ferroelectric PbZr(0.2)Ti(0.8)O3 (PZT) thin films is reported. A comparison of the properties of relaxed (tetragonality c/a approximately 1.05) and highly strained (c/a approximately 1.09) epitaxial films shows that polarization, while being amongst the highest reported for PZT or PbTiO3 in either film or bulk forms P(r) approximately 82 microC/cm(2)), is almost independent of the epitaxial strain. We attribute this behavior to a suppressed sensitivity of the A-site cations to epitaxial strain in these Pb-based perovskites, where the ferroelectric displacements are already large, contrary to the case of less polar perovskites, such as BaTiO3. In the latter case, the A-site cation (Ba) and equatorial oxygen displacements can lead to substantial polarization increases.     

High quality PdTe_2 thin films grown by molecular beam epitaxy

PdTe_2,a member of layered transition metal dichalcogenides(TMDs),has aroused significant research interest due to the coexistence of superconductivity and type-II Dirac fermions.It provides a promising platform to explore the interplay between superconducting quasiparticles and Dirac fermions.Moreover,PdTe_2 has also been used as a substrate for monolayer antimonene growth.Here in this paper,we report the epitaxial growth of high quality PdTe_2 films on bilayer graphene/SiC(0001)by molecular beam epitaxy(MBE).Atomically thin films are characterized by scanning tunneling microscopy(STM),X-ray photoemission spectroscopy(XPS),low-energy electron diffraction(LEED),and Raman spectroscopy.The band structure of 6-layer PdTe_2 film is measured by angle-resolved photoemission spectroscopy(ARPES).Moreover,our air exposure experiments show excellent chemical stability of epitaxial PdTe_2 film.High-quality PdTe_2 films provide opportunities to build antimonene/PdTe_2 heterostructure in ultrahigh vacuum for future applications in electronic and optoelectronic nanodevices.     

缓冲层对InSb/GaAs薄膜质量的影响

InSb是制作3~5μm红外探测器的重要材料。在GaAs衬底上外延生长InSb,存在的主要问题在于两种材料间14.6%的晶格失配度,会引入较大的表面粗糙度以及位错密度,使外延材料的结构和电学性能均会受到不同程度的影响。通过系列实验,研究了在生长过程中缓冲层对薄膜质量的影响。利用高能电子衍射仪(RHHEED)得到了合适的生长速率和Ⅴ/Ⅲ比,研究了异质外延InSb薄膜生长中低温InSb缓冲层对材料生长质量以及不同外延厚度对材料电学性质的影响。采用原子力显微镜(AFM)、透射电子显微镜(TEM)、X射线双晶衍射(DCXRD)等方法研究了InSb/GaAs薄膜的表面形貌、界面特性以及结晶质量。通过生长合适厚度的缓冲层,获得了室温下DCXRD半高峰宽为172″,77 K下迁移率为64300 cm²·V^-1·s^-1的InSb外延层。     

Raman spectroscopy study of lattice dynamics of macro-, micro-, and nanostructured barium titanates

The temperature dependences of the components A ₁(2TO) and E(1TO) of the soft ferroelectric mode during phase transitions in single crystals, ceramics, polycrystalline and epitaxial thin films of barium titanate, as well as a superlattice consisting of alternating layers of barium and strontium titanates, have been studied using the Raman spectroscopy method. Abrupt changes in soft mode frequencies have been observed in the single crystal during phase transitions between tetragonal, orthorhombic, and rhombohedral phases. Smoothing of the temperature dependences of soft modes and the coexistence of phases have been observed in ceramics and polycrystalline films. In the epitaxial film, the sequence of structural transformations fundamentally differs from that observed in the single crystal; in the superlattice, the ferroelectric phase is stable to 550 K.     

Heteroepitaxial film growth of layered compounds with the ZrCuSiAs-type and ThCr2Si2-type structures: From Cu-based semiconductors to Fe-based superconductors

FeAs-based layered superconductors such as F-doped LaFeAsO have recently been investigated intensively because of their high superconducting transition temperatures. Epitaxial films of these compounds are important to examine their intrinsic materials properties as well as to transfer them to device applications. In this review, we first present our research route from transparent p-type oxides semiconductors to the Fe-based superconductors. Then we review growth of epitaxial thin films for the layered oxychalcogenides and oxypnictides. Reactive solid-phase epitaxy technique was inevitable to prepare epitaxial thin films of the oxychalcogenides and Zn-based oxypnictides. On the other hand, epitaxial thin films of Mn-based oxypnictides were grown by standard pulsed laser deposition. These techniques, however, did not grow epitaxial thin films for LaFeAsO. Thus, we developed a modified pulsed laser deposition process and succeeded in obtaining epitaxial thin films of FeAs-based superconductors, LaFeAsO and cobalt-doped SrFe₂As₂.     

Terahertz generation and detection of LT-GaAs thin film photoconductive antennas excited by lasers of different wavelengths

A new method of generating and detecting terahertz waves is proposed. Low-temperature-grown gallium arsenide (LT-GaAs) thin films are prepared by etching a sacrificial layer (AlAs) in a four-layer epitaxial structure constituted with LT-GaAs, AlAs, GaAs, and semi-insulating gallium arsenide (SI-GaAs). The thin films are then transferred to clean silicon for fabricating the LT-GaAs thin film antennas. The quality and transmission characteristics of the films are analyzed by an 800-nm asynchronous ultrafast time domain spectroscopy system, and the degree of bonding between the film and silicon wafer is determined. Two LT-GaAs thin film antennas for generating and detecting the terahertz waves are tested with a 1550-nm femtosecond laser. The terahertz signal is successfully detected, proving the feasibility of this home-made LT-GaAs photoconductive antennas. This work lays a foundation for studying the mechanism of terahertz wave generation in GaAs photoconductive antennas below the semiconductor band gap.     

New source of stacking faults in heteroepitaxial systems

A new stacking fault formation mechanism has been observed for the first time in ZnO/LiTaO(3) heteroepitaxial films. High resolution electron microscopy studies combined with electron diffraction and numerical image computation suggest that the observed type I1 intrinsic stacking faults in an epitaxial film can be dominantly formed as a result of tilting of the lattices between films and substrate required to maintain a particular orientation relationship.     

温度对Si上MOCVD-ZnO成核与薄膜生长特性的影响

采用金属有机化学气相沉积(MOCVD)方法在Si衬底上进行了ZnO的成核与薄膜生长研究。ZnO薄膜的形貌和结晶特性由成核和后期生长过程共同决定,初期成核温度决定了其尺寸和密度,进而影响后期ZnO主层的生长行为,但由于高温对后期ZnO纳米柱横向生长的抑制,纳米柱的尺寸并没有因为成核尺寸的增大而变大,因此在560℃得到了晶柱尺寸最大、密度最小的ZnO薄膜。最后通过改变成核温度,优化了ZnO外延膜的结晶质量。     

CdSe epitaxial films and nanostructures grown by the isothermal closed space sublimation technique

The use of the isothermal closed space sublimation technique for growing CdSe very thin films and nanostructures is reported. In this technique, the samples are grown by exposing a substrate alternately to elemental sources of Cd and Se. The whole system is at the same temperature, so the only driving force for the film growth is the vapour pressure difference between the elemental source and the film surface. This is due to the difference in chemical potential between the pure elements and the elements when forming the compound. Between subsequent exposures the surface is exposed to the carrier vapour. In this step, re-evaporation of the non-stable outermost part of the films can be controlled. This procedure leads to a self-regulated growth rate in which the size of the deposited materials is controlled very accurately. In this way, nanostructures and epitaxial thin films of CdSe were grown on single-crystal substrates. For the nanostructure growth a nanoporous anodic alumina membrane (AAM) was interposed between the elemental sources and the substrate. Optical and structural properties of the structures are reported. The structural characterization using x-ray diffraction and high resolution electron microscopy reveals the epitaxial quality of the films and the chemical composition and morphology of the semiconductor filled AAM samples.     

Domain epitaxial growth of ferroelectric films of barium strontium titanate on sapphire

A model of the epitaxial growth of crystalline multicomponent films on single-crystal substrates with a domain correspondence is presented using a solid solution of barium strontium titanate on sapphire substrates (r cut). The domain epitaxial growth suggests the matching of the lattice planes of the film and the substrate having similar structures by comparison of domain multiple of an integral number of the interplanar spacings. Variation of the component composition of the solid solution enables changes in the domain size in the range sufficient for epitaxial growth. This method can be used to project the epitaxial growth of films of various solid solutions on single-crystal substrates.     

A nanoindentation analysis of the influence of lattice mismatch on some wide band gap semiconductor films

Nanoindentation studies are carried out on epitaxial ZnO and GaN thin films on (0 0 0 1) sapphire and silicon substrates, respectively. A single discontinuity (‘pop-in’) in the load-indentation depth curve is observed for ZnO and GaN films at a specific depths of 13-16 and 23-26 nm, respectively. The physical mechanism responsible for the ‘pop-in’ event in these epitaxial films may be due to the interaction behavior of the indenter tip with the pre-existing threading dislocations present in the films during mechanical deformation. It is observed that the ‘pop-in’ depth is dependent on lattice mismatch of the epitaxial thin film with the substrate, the higher the lattice mismatch the shallower the critical ‘pop-in’ depth.