Strain accommodation of 3C-SiC grown on hydrogen-implanted Si (001) substrate

The hydrogen-implanted Si substrate has been used for the fabrication of the "compliant substrate", which can accommodate the mismatch strain during the heteroepitaxy. The compliance of the substrate can be modulated by the energy and dose of implanted hydrogen. In addition, the defects caused by implantation act as the gettering center for the internal gettering of the harmful metallic impurities. Compared with SiC films growth on substrate without implantation. all the measurements indicated that the mismatch strains in the SiC films grown on this substrate have been released and the crystalline qualities have been improved. It is a practical technique used for the compliant substrate fabrication and compatible with the semiconductor industry. (C) 2003 Elsevier B.V. All rights reserved.

In0.25Ga0.75As films growth on the thin GaAs/AlAs buffer layer on the GaAs(001) substrate

Thin GaAs/AlAs and GaAs/GaAs buffer layer structure have been fabricated on the GaAs(001) substrate. The top GaAs buffer layer is decoupled from the host substrate by introduction of a low temperature thin interlayer (AlAs or GaAs), which was mechanically behaved like the compliant substrate. Four hundred nanometer In0.25Ga0.75As films were grown on these substrates and the traditional substrate directly. Photoluminescence (PL), double-crystal X-ray diffraction (DCXRD) and atomic force microscopy (AFM) measurements were used to estimate the quality of the In0.25Ga0.75As layer and the compliant effects of the low temperature buffer layer. All the measurements shown that the qualities of epilayer have been improved and the substrate have been deteriorated severely. The growth technique of the thin GaAs/AlAs structure was found to be simple but very powerful for heteroepitaxy. (C) 2003 Elsevier Science B.V All rights reserved.

The growth morphologies of GaN layer on Si(111) substrate

The growth morphologies of metalorganic chemical vapor deposition (MOCVD) grown GaN layer on Si(111) substrate were studied using atomic force microscopy and transmission electron microscopy. It was found that the growth process of GaN/Si(111) consisted of two cycles of island growth and coalescence. These two cycles process differs markedly from that of one cycle process reported. The stress of evolving GaN layers on Si(111) was characterized by measuring the lattice constant c of GaN using X-ray diffraction (XRD) technique. It was proposed that the large tensile stress within the film during growth initiated this second island growth cycle, and the interaction between the GaN islands with high orientational fluctuation on the buffer layer induced this large tensile growth stress when coalescence occurred. (C) 2002 Elsevier Science B.V. All rights reserved.

In0.25Ga0.75As growth on low-temperature thin buffer layers formed on GaAs (001) substrate

High-quality In0.25Ga0.75As films were grown on low-temperature (LT) ultra-thin GaAs buffer layers formed on GaAs (0 0 1) substrate by molecular beam epitaxy. The epilayers were studied by atomic force microscopy (AFM), photo luminescence (PL) and double crystal X-ray diffraction (DCXRD), All the measurements indicated that LT thin buffer layer technique is a simple but powerful growth technique for heteroepitaxy. (C) 2002 Elsevier Science B.V. All rights reserved.

Strain relaxation of InP film directly grown on GaAs patterned compliant substrate

In order to overcome the large lattice mismatch in the heteroepitaxy, a new patterned compliant substrate method has been introduced, which has overcome the disadvantages of previously published methods. InP film of thickness 800 nm was directly grown on this substrate. Scanning electron microscopy (SEM) has shown that good surface morphology has been obtained. In addition, Photoluminescence (PL) and double crystal X-ray diffraction (DCXRD) study have shown that the residual strain has been reduced, and that the structure quality has been improved. (C) 2002 Elsevier Science B.V. All rights reserved.

Investigation of GaN layer grown on Si(111) substrate using an ultrathin AlN wetting layer

High-quality GaN epilayers were grown on Si (1 1 1) substrate by metalorganic chemical vapor deposition. The growth process was featured by using an ultrathin AlN wetting layer (WL) in combination with a low-temperature (LT) GaN nucleation layer (NL). The full-width at half-maximum (FWHM) of the X-ray rocking curve for the GaN (0 0 0 2) diffraction was 15 arcmin. The dislocation density estimated from TEM investigation was found to be of the order of 10(9)cm(-2). The FWHM of the dominant band edge emission peak of the GaN was measured to be 47 meV by photoluminescence measurement at room temperature. The ultrathin AlN WL was produced by nitridation of the aluminium pre-covered substrate surface. The reflection high-energy electron diffraction showed that the AlN WL was wurtzite and the surface morphology was like the nitridated surface of sapphire by the atomic force microscopy measurement. X-ray photoelectron spectroscopy measurement showed that Si and SixNy at a certain concentration were intermixed in the AlN WL. This study suggests that by employing an appropriate WL combined with a LT NL, high-quality heteroepitaxy is achievable even with large mismatch. (C) 2002 Elsevier Science B.V. All rights reserved.

Hydrogen-dependent lattice dilation in GaN

Using Raman spectroscopy we have analysed the strain status of GaN films grown on sapphire substrates by NH3 source molecular beam epitaxy (MBE). In addition to the expected compressive biaxial strain, in some cases GaN films grown on c-face sapphire substrates suffer from serious tensile biaxial strain. This anomalous behaviour has been well interpreted in terms of interstitial hydrogen-dependent lattice dilation. The hydrogen concentration in the films is measured by nuclear reaction analysis (NRA). With increasing hydrogen incorporation, the residual compressive biaxial strain is first further relaxed, and then turns into tensile strain when the hydrogen contaminant exceeds a critical concentration. The hydrogen incorporation during the growth process is found to be growth-rate dependent, and is supposed to be strain driven. We believe that the strain-induced interstitial incorporation is another way for strain relaxation during heteroepitaxy, besides the two currently well known mechanisms: formation of dislocations and growth front roughening.

Surface morphology evolution of strained InAs/GaAs(331)a films

Surface morphology evolution of strained InAs/GaAs(331)A films was systematically investigated in this paper. Under As-rich conditions, InAs elongated islands aligned along [1 (1) over bar0] are formed at a substrate temperature of 510 degrees C. We explained it as a result of the anisotropic diffusion of adatoms. Under In-rich conditions, striking change has occurred with respect to the surface morphology of the InAs layers. Instead of anisotropic InAs elongated islands, unique island-pit pairs randomly distributed on the whole surface were observed. Using cooperative nucleation mechanisms proposed by Jesson et al. [Phys. Rev. Lett. 77, 1330 (1996)], we interpret the resulting surface morphology evolution.

CONSTRUCTION AND APPLICATIONS OF A DUAL MASS-SELECTED LOW-ENERGY ION-BEAM SYSTEM

A direct ion beam deposition system designed for heteroepitaxy at a low substrate temperature and for the growth of metastable compounds has been constructed and tested. The system consists of two mass-resolved low-energy ion beams which merge at the target with an incident energy range 50-25 000 eV. Each ion beam uses a Freeman ion source for ion production and a magnetic sector for mass filtering. While a magnetic quadrupole lens is used in one beam for ion optics, an electrostatic quadrupole lens focuses the other beam. Both focusing approaches provide a current density more than 100-mu-A/cm2, although the magnetic quadrupole gives a better performance for ion energies below 200 eV. The typical current of each beam reaches more than 0.3 mA at 100 eV, with a ribbon beam of about 0.3-0.5 x 2 cm2. The target is housed in an ultrahigh vacuum chamber with a base pressure of 1 x 10(-7) Pa and a typical pressure of 5 x 10(-6) Pa when a noncondensable beam like argon is brought into the chamber. During deposition, the target can be heated to 800-degrees-C and scanned mechanically with an electronic scanning control unit. The dual beam system has been used to grow GaN using a Ga+ and a N+ beam, and to study the oxygen and hydrogen ion beam bombardment effects during carbon ion beam deposition. The results showed that the simultaneous arrival of two beams at the target is particularly useful in compound formation and in elucidation of growth mechanisms.

PHOTOLUMINESCENCE AND SURFACE PHOTOVOLTAIC SPECTRA OF STRAINED INP ON GAAS

A high energy shift of the band-band recombination has been observed in the photoluminescence (PL) spectra of the strained InP epilayer on GaAs by metalorganic chemical vapor deposit. The strain determined by PL peak is in good agreement with calculated thermal strain. The surface photovoltalic spectra gives the information about energy gap, lattice mismatching, and composition of heteroepilayers, diffusion length, surface, and interface recombination velocity of minority carriers of heteroepitaxy layers.

A model of dislocations at the interface of the bonded wafers

Wafer bonding is regardless of lattice mismatch in the integration of dissimilar semiconductor materials. This technology differs from the heteroepitaxy mainly in the mechanism of generating dislocations at the interface. A model of dislocations at the bonded interface is proposed in this paper. Edge-like dislocations, which most efficiently relax the strain, are predominant at the bonded interface. But the thermal stress associated with large thermal expansion misfit may drive dislocations away from the bonded interface upon cooling.

Weak epitaxy growth of metal-free phthalocyanine on p-sexiphenyl monolayer and double-layer films

Weak epitaxy growth (WEG) can afford high-mobility thin films of disk-like organic semiconductor of which mobility is up to the level of the corresponding single crystals. We investigated the WEG behavior and mechanism of planar phthalocyanine in the model system of metal-free phthalocyanine (H2Pc) grown on p-sexiphenyl (p-6P) ultrathin films (monolayers and double layers). Highly oriented H2Pc films with molecules standing up exhibited two kinds of different in-plane orientations, i.e., three sets of in-plane orientations and only one set of in-plane orientation, on p-6P monolayer and double-layer films, respectively.

A novel epitaxy of isotactic polypropylene (alpha phase) on PTFE and organic substrates

Isotactic polypropylene in its a modification (alpha iPP) crystallises epitaxially on polytetrafluoroethylene (PTFE) and several hemiacids or salts of substituted benzoic acids via a novel contact plane, namely (110): so far, the only known contact plane involved in alpha iPP homo- and hetero-epitaxies was (010). In spite of its complicated architecture (alternation of antichiral helices with different azimuthal settings), the (110)(alpha iPP) contact plane displays well defined, if not prominent, rows of methyl side chains parallel to the crystallographic (112) direction (at 57 degrees to the c-axis) and approximate to 5.5 Angstrom apart. The matching contact planes of the substrates display linear gratings made of rows of e.g. chlorine atoms or PTFE chains with similar approximate to 5.5 Angstrom inter-row or interchain distances. Various morphologies are observed in iPP thin films crystallised at different cooling rates in the presence of PTFE; they can be analysed in terms of a succession and interplay of successive epitaxies: initial alpha iPP/PTFE heteroepitaxy, followed by alpha iPP/alpha iPP and gamma iPP/alpha iPP homoepitaxies. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.

Critical crystallization temperature for the occurrence of epitaxy between high-density polyethylene and isotactic polypropylene

The crystallization behavior of high-density polyethylene (HDPE) on highly oriented isotactic polypropylene (iPP) at elevated temperatures (e.g., from 125 to 128 degrees C), was studied using transmission electron microscopy and electron diffraction. The results show that epitaxial crystallization of HDPE on the highly oriented iPP substrates occurs only in a thin layer which is in direct contact with the iPP substrate, when the HDPE is crystallized from the melt on the oriented iPP substrates at 125 degrees C. The critical layer thickness of the epitaxially crystallized HDPE is not more than 30 nm when the HDPE is isothermally crystallized on the oriented iPP substrates at 125 degrees C. When the crystallization temperature is above 125 degrees C, the HDPE crystallizes in the form of crystalline aggregates and a few individual crystalline lamellae. But both the crystalline aggregates and the individual crystalline lamellae have no epitaxial orientation relationship with the iPP substrate. This means that there exists a critical crystallization temperature for the occurrence of epitaxial crystallization of HDPE on the melt-drawn oriented iPP substrates (i.e., 125 degrees C). (C) 1997 John Wiley & Sons, Inc.

Epitaxial recrystallization of HDPE-quenched ultrathin films on oriented iPP substrates

The recrystallization behavior of high-density polyethylene (HDPE) on the highly oriented isotactic polypropylene (iPP) substrates at temperatures below the melting temperature of HDPE has been investigated by means of transmission electron microscopy. The results obtained by the bright-field observation and the electron diffraction show that upon annealing the HDPE-quenched films on the oriented iPP substrates at temperatures below 125 degrees C, only a small amount of HDPE recrystallizes on the iPP substrate with [001](HDPE)//[001](iPP), while annealing the HDPE-quenched films at temperatures above 125 degrees C, all of the HDPE crystallites recrystallize epitaxially on the iPP substrate with [001](HDPE)//[101](iPP). (C) 1997 John Wiley & Sons, Inc.