Growth of highly disordered InGaP on (100) GaAs by molecular beam epitaxy with a GaP decomposition source

High-quality, lattice-matched InGaP on exact (100) GaAs was successfully grown by molecular beam epitaxy with a GaP decomposition source. The ordering parameter (η) of the InGaP is investigated as a function of the growth temperature. η is as low as 0.22 and almost insensitive to the growth temperature below 460 °C. It increases abruptly around 475 °C and has a maximum value of 0.35 at ≈490 °C. Double crystal X-ray diffraction and a low-temperature photoluminescence spectrum reveal that the present growth method is robust and provides better quality InGaP compared to other state-of-the-art growth technologies. Received: 20 November 2000 / Accepted: 27 January 2001 / Published online: 21 March 2001     

Reflection high-energy electron diffraction real-time monitoring of an etch process implemented in molecular beam epitaxy technology: hydrogen chloride versus GaAs(001) epilayers

Received: 13 November 1997/Accepted: 19 January 1998     

High Quality AlN with a Thin Interlayer Grown on a Sapphire Substrate by Plasma-Assisted Molecular Beam Epitaxy

We report an AlN epi-layer grown on sapphire by plasma-assisted molecular beam epitaxy with a thin interlayer structure. The effects of growth mode on threading dislocations (TDs) and surface morphology are studied. Then an interlayer structure grown under a V/Ⅲ ratio of 1 is adopted to improve the AlN crystalline quality. By optimizing the thickness of the interlayer, the TD density and surface roughness can be reduced simultaneously.     

Hydride vapor phase epitaxy growth of GaN on sapphire with ZnO buffer layers

The initial stages and subsequent growth of GaN on sapphire using ZnO buffer layers is reported for the hydride vapor phase epitaxy technique. A high gas-phase supersaturation in the growth ambient was used to favor a rapid initial growth on the substrate. A subsequent growth step was employed under conditions that favor a high lateral growth rate in order to promote the coalescence of the initial islands and provide optimal material properties. The specific gas-phase mole fractions of the GaCl and NH₃ at the growth front control both the vertical and lateral growth rates. The use of a two-step growth process in the GaN growth leads to a controlled morphology and improved material properties for GaN materials when grown with a ZnO buffer layer. An optimized set of growth conditions, utilizing this two-step process, was found to also improve the growth directly on sapphire without a ZnO buffer layer. Received: 8 November 2001 / Accepted: 14 November 2001 / Published online: 11 February 2002     

Area-selective epitaxy of GaAs by migration-enhanced epitaxy with As2 and As4 arsenic sources

We demonstrate area-selective epitaxy by migration-enhanced epitaxy with As₂ and As₄ as arsenic sources. The distinct whisker structure growing in [1 1 1]B direction is obtained when employing As₂ as an arsenic source, while (1 1 1)B facet is formed with As₄. The difference in the facet formation can be explained by the formation of As-trimer, which significantly reduces the growth rate of the (1 1 1)B surface. With As₂, area-selective epitaxy can be achieved at lower arsenic pressure condition, where less As-trimers are formed. Therefore, growth in the [1 1 1]B direction is enhanced.     

Morphological and luminescent characteristics of GaN dots deposited on AlN by alternate supply of TMG and NH3

GaN dots were deposited on AlN underlayers by alternate supply of trimethylgallium (TMG) and ammonia (NH₃) in an inductively heated quartz reactor operated at atmospheric pressure. Various growth parameters including deposition temperature, TMG admittance and pulse time between TMG and NH₃ exposures were proposed to investigate the influence of growth parameters on the size distribution of GaN dots. It appears that GaN dots with uniform size distribution can be achieved under certain growth conditions. Based on the study of atomic force microscopy (AFM), high deposition temperature was found to be in favor of forming large GaN dots with small dot density. Decrement of TMG flow rate or reduction in the number of growth cycle tends to enable the formation of GaN dots with small dot sizes. The results of room temperature (RT) cathodoluminescence (CL) measurements of the GaN dots exhibit an emission peak at 3.735 eV. A remarkable blue shift of GaN dot emission was observed by reduced temperature photoluminescence (PL) measurements.     

An effective compliant substrate for low-dislocation relaxed Si1-xGex growth

An effective compliant substrate for Si_1-xGe_x growth is presented. A silicon-on-insulator substrate was implanted with B and O forming 20 wt % borosilicate glass within the SiO₂. The addition of the borosilicate glass to the buried oxide acted to reduce the viscosity at the growth temperature of Si_1-xGe_x, promoting the in situ elastic deformation of the thin Si (∼20 nm) layer on the insulator. The sharing of the misfit between the Si and the Si_1-xGe_x layers was observed and quantified by double-axis X-ray diffraction. In addition, the material quality was assessed using cross-sectional transmission electron microscopy, photoluminescence and etch pit density measurements. No misfit dislocations were observed in the partially relaxed 150-nm Si_0.75Ge_0.25 sample as-grown on a 20% borosilicate glass substrate. The threading dislocation density was estimated at 2×10⁴ cm^-2 for 500-nm Si_0.75Ge_0.25 grown on the 20% borosilicate glass substrate. This method may be used to prepare compliant substrates for the growth of low-dislocation relaxed SiGe layers. Received: 4 January 2001 / Accepted: 30 May 2001 / Published online: 17 October 2001     

Surface preparation effect of GaAs(110) substrates on the ZnSe epitaxial layer grown by molecular beam epitaxy

The effect of the surface preparation of the GaAs(110) substrate on the ZnSe epitaxial layer grown by molecular beam epitaxy (MBE) was investigated by means of etch-pit density (EPD) measurements, surface morphology observation, and reflection high-energy electron diffraction (RHEED) analysis. The ZnSe epitaxial layer grown on a GaAs(110) surface prepared by cleaving the (001)-oriented wafer in ultrahigh vacuum (UHV) showed about 5×10⁴ cm^-2 of EPD. This value is much lower than that observed from both the samples grown on the mechanically polished surface with and without a GaAs buffer layer. Due to the non-stoichiometric surface after thermal evaporation of the surface oxide, three-dimensional growth can easily occur on the mechanically polished GaAs(110) substrate. These results suggest that the stoichiometric and atomically flat substrate surface is essential for the growth of low-defect ZnSe epitaxial layers on the GaAs(110) non-polar surface. Received: 21 August 1998 / Accepted: 19 October 1998 / Published online: 28 April 1999     

Ordered InAs Quantum Dots with Controllable Periods Grown on Stripe-Patterned GaAs Substrates

GaAs （001） substrates are patterned by electron beam lithography and wet chemical etching to control the nucleation of lnAs quantum dots （QDs）. InAs dots are grown on the stripe-patterned substrates by solid source molecular beam epitaxy. A thick buffer layer is deposited on the strip pattern before the deposition of InAs. To enhance the surface diffusion length of the In atoms, InAs is deposited with low growth rate and low As pressure. The AFM images show that distinct one-dimensionally ordered InAs QDs with homogeneous size distribution are created, and the QDs preferentiMly nucleate along the trench. With the increasing amount of deposited InAs and the spacing of the trenches, a number of QDs are formed beside the trenches. The distribution of additional QDs is long-range ordered, always along the trenchs rather than across the spacing regions.     

Effect of Nitridation on Morphology, Structural Properties and Stress of AlN Films

We investigate effects of nitridation on AlN morphology, structural properties and stress. It is found that 3min nitridation can prominently improve AlN crystal structure, and slightly smooth the surface morphology. However, 10min nitridation degrades out-of-plane crystal structure and surface morphology instead. Additionally, 3-min nitridation introduces more tensile stress （1.5 GPa） in AlN films, which can be attributed to the weaker islands 2D coalescent. Nitridation for lOmin can introduce more defects, or even forms polycrystallinity interlayer, which relaxes the stress. Thus, the stress in AlN with 10 min nitridation decreases to -0.2 GPa compressive stress.     

Morphologies of GaN one-dimensional materials

GaN one-dimensional materials with different morphologies were formed on LaAlO₃ crystal, silicon crystal and quartz glass substrates through a simple sublimation method. They were characterized by powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM) and energy-dispersive X-ray (EDX) spectroscopy. FE-SEM images showed that the morphologies of the one-dimensional materials included straight nanorods, curved nanowires, nanoribbons, zigzag nanorods and beaded or capture-tree nanorods. XRD and EDX studies indicated that all the one-dimensional materials were wurtzite GaN. Received: 14 July 2000 / Accepted: 17 July 2000 / Published online: 20 September 2000     

Fabrication of bamboo-shaped GaN nanorods

Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated that the nanorods were single-crystal wurtzite GaN. Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001     

Transmission electron microscopy study of vertical quantum dots molecules grown by droplet epitaxy

The compositional distribution of InAs quantum dots grown by molecular beam epitaxy on GaAs capped InAs quantum dots has been studied in this work. Upper quantum dots are nucleated preferentially on top of the quantum dots underneath, which have been nucleated by droplet epitaxy. The growth process of these nanostructures, which are usually called as quantum dots molecules, has been explained. In order to understand this growth process, the analysis of the strain has been carried out from a 3D model of the nanostructure built from transmission electron microscopy images sensitive to the composition.     

Molecular Beam Epitaxy of GaSb on GaAs Substrates with AlSb Buffer Layers

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using AlSb buffer layers. Optimization of AlSb growth parameter is aimed at obtaining high GaSh crystal quality and smooth GaSh surface. The optimized growth temperature and thickness of AlSb layers are found to be 450℃ and 2.1 nm, respectively. A rms surface roughness of 0.67 nm over 10 × 10 μm^2 is achieved as a 0.5 μm GaSh film is grown under optimized conditions.     

Preferential regrowth of indium–tin oxide (ITO) films deposited on GaN (0001) by rf-magnetron sputter

Effects of thermal treatments on the electrical properties and microstructures of indium–tin oxide (ITO)/GaN contacts have been investigated using a rf-magnetron sputter deposition followed by rapid thermal annealing. ITO films annealed at 800 °C revealed Schottky contact characteristics with a barrier height corresponding to ITO’s work function of 4.62 eV. The evolution of electrical properties of ITO/GaN contacts was attributed to the preferential regrowth of In₂O₃ (222)//GaN (0001) with an ideal metal–semiconductor Schottky contact. The feasible use of ITO/GaN as a transparent Schottky contact would be realized by the enhanced regrowth of In₂O₃ at high temperature. Received: 1 September 2000 / Accepted: 15 November 2000 / Published online: 28 February 2001     

A Comparison between AlN Films Grown by MOCVD Using Dimethylethylamine Alane and Trimethylaluminium as the Aluminium Precursors

Aluminium nitride (AlN) films grown with dimethylethylamine alane (DMEAA) are compared with the ones grown with trimethylaluminium (TMA). In the high-resolution x-ray diffraction Ω scans, the full width at half maximum (FWHM) of (0002) AlN films grown with DMEAA is about 0.70 deg, while the FWHM of (0002) AlN films grown with TMA is only 0.11 deg. The surface morphologies of the films are different, and the rms roughnesses of the surface are approximately identical. The rms roughness of AlN films grown with DMEAA is 47.4nm, and grown with TMA is 69.4nm. Although using DMEAA as the aluminium precursor cannot improve the AlN crystal quality, AlN growth can be reached at low temperature of 673K. Thus, DMEAA is an alternative aluminium precursor to deposit AlN film at low growth temperatures.     

In situ optical monitoring of metalorganic vapor phase epitaxy growth of C-doped GaAs

20 cm^-3 and above) induce oscillations in the reflected intensity. The evolution of the layers morphology is shown to depend on two effects: (i)the locally high surface concentration of carbon which blocks locally the growth and hence induces holes at the surface, (ii)the occurrence of dislocations at thicknesses larger than the critical thickness which are revealed chlorides produced by the decomposition of CCl₄ (the carbon precursor) and form deep etch pits. Received: 13 February 1998 / Accepted: 26 October 1998     

Epitaxial growth and spectroscopic investigation of BaSO4:Mn6+ layers

We report on the first layer growth of a Mn⁶⁺-doped material. Large-size BaSO₄ substrates of 10×6×4 mm³ were grown from a LiCl solvent by the flux method. Flat surfaces of undoped BaSO₄ were then achieved by use of liquid-phase epitaxy (LPE) from a CsCl–KCl–NaCl solvent. Finally, BaSO₄:Mn⁶⁺ layers were grown by LPE with growth velocities of approximately 3 μm h^-1, at temperatures of 550–508 °C. Absorption, luminescence, luminescence-excitation and luminescence-decay measurements confirmed the incorporation of manganese solely in its hexavalent oxidation state. This material possesses potential as a near-infrared tunable laser with a wavelength range larger than Ti:sapphire. Received: 7 January 2002 / Revised version: 30 March 2002 / Published online: 8 August 2002     

Effects of In and Sb mono-layers to form rotated InSb films on a Si(1 1 1) substrate

A new method for InSb heteroepitaxial growth on a Si substrate was introduced in our previous work, in which an InSb film was formed via an InSb bi-layer. In the present work, to study the effects of In and Sb individual layers on the InSb film quality, InSb was deposited onto an InSb bi-layer, In mono-layer, and Sb mono-layer on a Si substrate. It was found that both In and Sb layers (in other words, InSb bi-layer) were essential to form a fine InSb film.     

Growth of Strain Free GaN Layers on （0001） Oriented Sapphire by Using Quasi-Porous GaN Template

We report the reduced-strain gallium-nitride （GaN） epitaxial growth on （0001） oriented sapphire by using quasiporous GaN template. A GaN film in thickness of about 1 μm was initially grown on a （0001） sapphire substrate by molecular beam epitaxy. Then it was dealt by putting into 45% NaOH solution at 100℃ for lOmin. By this process a quasi-porous GaN film was formed. An epitaxial GaN layer was grown on the porous GaN layer at 1050℃ in the hydride vapour phase epitaxy reactor. The epitaxial layer grown on the porous GaN is found to have no cracks on the surface. That is much improved from many cracks on the surface of the GaN epitaxial layer grown on the sapphire as the same as on GaN buffer directly.