Yue Long Huang

Cubic boron nitride thin film heteroepitaxy

In this study we investigate the possibility of nucleating nanocrystalline cubic boron nitride (c-BN) thin films directly onto suitable substrates without the soft turbostratic BN (t-BN) interlayer that is usually observed. This would open a path to the epitaxial growth of c-BN films which is essential particularly for practicable applications in electronic devices. Appropriate substrates are required to exhibit a lattice that matches the c-BN crystallite structure, survives the ion bombardment imperative for c-BN film formation, and is not disturbed by the development of a heterogeneous interface layer. In accordance with these criteria, monocrystalline AlN is selected and employed as a potential substrate for direct c-BN film growth using mass selected ion beam deposition. A detailed examination of the BN/AlN interface microstructure by cross-sectional high-resolution transmission electron microscopy reveals that the AlN crystallinity is indeed retained, with no amorphous layer next to the BN film as co...

Ion beam synthesis of amorphous carbon thin films containing metallic nanoclusters

Abstract We investigated the synthesis of metallic nanoparticles during growth of an amorphous carbon matrix using mass selected ion beam deposition of carbon and metal ions. By varying the carbon-to-metal ion ratio, a-C:Cu and a-C:Ag films with metal concentrations between 0 and 50 at.% were grown at room temperature on Si substrates by co-deposition of low energy mass-selected 12 C + , 63 Cu + and 107,109 Ag + ions. X-ray diffraction and transmission electron microscopy reveal metal particles with diameters of a few nanometers. The matrix is diamond-like with mainly sp 3 -bonded carbon at low metal concentrations and becomes graphitic for metal concentrations exceeding 10 at.%. Whereas a large fraction of the deposited Cu ions are incorporated into the films, most of the deposited Ag ions have disappeared. The residual Ag accumulates at the surface and at the C/Si interface. Furthermore, the interface roughness of a-C:Ag films on Si is high. These observations are discussed in terms of the stability of small Ag clusters and Ag induced interface reactions.

Structural and optical properties of β-FeSi2 layers grown by ion beam mixing

Abstract This study deals with structural and optical properties of β-FeSi 2 layers produced by direct ion beam mixing of Fe/Si bilayers with Xe ions. By irradiation of 35 nm Fe on Si, at 600 °C with 205 keV Xe to 2×10 16 ions/cm 2 , the formation of ∼105 nm single-phase β-FeSi 2 layers was achieved. Their structures were analyzed by Rutherford backscattering spectroscopy, X-ray diffraction, conversion electron Mossbauer spectroscopy, high resolution transmission electron microscopy, and photo-absorption. The structural analyses revealed that the β-FeSi 2 layers grow in the form of irregularly shaped crystal grains, with a pronounced surface morphology, but with a rather sharp silicide/silicon interface. The grains that originate from the interface are epitaxially oriented relative to the Si(100) substrate. Optical absorption, as compared with that in β-FeSi 2 layers produced by ion beam synthesis or co-sputter deposition, indicates a direct band gap of 0.92 eV. A pronounced surface roughness of the ion beam mixed layers yielded photo-absorption approximately three times higher as compared with the other two sets of samples. The band gap stays nearly constant over the temperature range from 80 to 295 K. This is tentatively assigned to a high degree of structural disorder and stress induced in the ion beam mixed β-FeSi 2 layers.

NONCONSERVATIVE OSTWALD RIPENING OF DISLOCATION LOOPS IN SILICON

We have investigated the effects of the proximity of the surface on the ripening behavior of dislocation loops in preamorphized silicon. Starting from well-defined initial conditions, we have varied the location depth of the loops by successive chemical removal of surface layers and measured changes of the size–distribution function during subsequent annealing by means of transmission electron microscopy. Our results show that the amount of Si atoms bound in the loops is not conserved during annealing and that the loop location depth has a prominent effect on the ripening kinetics. Both these observations prove the nonconservative nature of Ostwald ripening of dislocation loops near wafer surfaces. In addition, we observed different ripening kinetics for annealing in vacuum and in Ar which show that different boundary conditions at the surface are established during annealing in these two ambients.

Raman scattering and growth disorders in single as-grown TiO2 nanowires

An oxidation procedure has been developed to grow single-crystalline TiO(2) nanowires of the pure rutile phase, allowing subsequent characterizations of SEM, XRD, Raman, and TEM without any post-growth preparations. TEM observations support that the 1D anisotropic growth is dominated by oriented attachment processes, leading to typical growth-induced defects in the nanowires. Spatial variations of the rutile E(g) and A(1g) Raman modes were unambiguously revealed on single nanowires while scanned along the growth direction parallel to the rutile [110]. Symmetry-sensitive deviations were identified by comparing the Raman data with the spatial correlation model calculations based on realistic dispersion relations of the rutile, reflecting morphology-correlated defect distributions along single nanowires. This work provides an efficient, non-destructive in situ characterization approach for guiding growth design in future nanotechnology.

µ-Raman Investigations on Hydrogen Gettering in Hydrogen Implanted and Hydrogen Plasma Treated Czochralski Silicon

µ-Raman measurements were carried out on hydrogen implanted, plasma hydrogenated and subsequently annealed Cz Silicon samples, respectively. In comparison to as-implanted or asplasma treated samples, in consideration of the thermal evolution, the effects of the implanted and subsequently plasma treated samples were analyzed. An enhanced trapping of molecular hydrogen in multivacancies has been observed after hydrogen implantation and subsequent plasma hydrogenation. In comparison to as-implanted samples, the intensity of the local vibrational modes (LVM) of vacancy-hydrogen complexes and silicon-hydrogen bonds are increasing.

DLTS study on deep levels formed in plasma hydrogenated and subsequently annealed silicon

P-n junctions are created in p-type Czochralski silicon after a low temperature (270°C) hydrogen plasma exposure. This is attributed to the formation of hydrogen-related shallow donors. A deep level (E1) with an activation energy of about EC-0.12 eV is observed by DLTS measurement and assigned to a metastable state of the hydrogen-related shallow donors. At an annealing temperature of 340°C, the E1 centres disappear and oxygen thermal donors appear. The concentrations of the oxygen thermal donors are found typically to be 2-3 decades lower than that required for over-compensating the initial p-type doping and for contributing the excess free carriers.

Depth Resolved Defect Analysis by Micro-Raman Investigations of Plasma Hydrogenated Czochralski Silicon Wafers

Depth resolved μ-Raman measurements were carried out on plasma hydrogenated and annealed silicon samples. The plasma exposure was done at 260 270 °C, and subsequent annealing at 450 °C or 550 °C. A thin structured plasma damage layer up to 100 150 nm depth and a subsurface layer up to a depth of ∼ 1 μm were observed by cross-sectional transmission electron and atomic force microscopy. In the subsurface region (111)and (100)-oriented platelets are located. Si-H Raman modes attributed to the plasma damage at the wafer surface exhibit a significant higher intensity than those attributed to platelets in the subsurface region. H2 molecules are located in the platelets, as was clearly seen by the fact that the H2 Raman signal exhibits a maximum in the intermediate subsurface region, where the platelets are located. After annealing hydrogen is released from the surface damage layer, while at the platelets it is still trapped.

Epitaxial Growth Due to Phase Separation of Disordered Eutectic Au:Si Alloys on Silicon

Epitaxial growth of gold on Si(100) from disordered Au:Si alloys has be en studied by in situ reflection high energy electron diffraction and ex situ trans mis ion electron microcopy. It is shown that different orientation relationships are formed depending on whet her the disordered alloy is the eutectic melt or a disordered phase resulting from the react ion of silicon and deposited Au:Si thin films at temperatures far below the eutectic temperature. Thi s observation is taken as evidence that the latter phase is a solid amorphous phase with near-eutectic composition. Introduction Thin film epitaxial growth is usually discussed in terms of mic ros opic processes which involve surface diffusion and incorporation of monomers into specific sites. The rates describing these processes have to be compared with the deposition rate when the possibili ty of epitaxial growth is considered. In fact, the critical deposition rate below which epitaxi al growth is observed is well described in terms of an Arrhenius law reflecting the thermally activated processes [1]. For the case that atomic transport in the deposited film and across the film/subs trate interface becomes appreciable, growth, structure and composition of the film will depend on t he relative magnitude of the deposition rates of the deposited species and the rates describing the above processes. We have recently shown by in situ Reflection High Energy Electron Diffra ction, RHEED, that during molecular beam epitaxial (MBE) growth of pure gold on Si(100) at 116°C a crystalline phase develops from a disordered phase. The crystalline phase is stabilize d y the molecular beam and transforms within 25s into a disordered phase when the deposition stops [2]. The formation of a disordered (amorphous) phase with near-eutectic composition plays an impor tant r le in the growth of gold on silicon (e.g. [3-7]). It is thought that the enormous strain energ y r sulting from the large misfit between crystalline gold and silicon is partly relaxed by the int ermixing of the two elements which leads to growth of the amorphous alloy. Its near-eutectic composition i s understood in terms of bulk thermodynamics of the Au:Si system [8] which has a deep eutectic at xE=18,6at% Si and T E=363°C [9] implying a high stability of the melt at x E with respect to crystalline phases. In our previous work [2] we have observed epitaxial growth of crystalli ne gold islands on Si(100) during co-deposition of gold and silicon for temperatures as low as 65°C a nd rel tive deposition rates of gold and silicon corresponding to near-eutectic compositions. Our RHEED experiments showed that the formation of a disordered phase is the pre-requisite for epi taxial growth (see below). The latter results from the decomposition of the disordered phase into cry stalline gold and silicon. Although in situ RHEED provided clear evidence for the occurrence of a disordered phase it could not be decided whether it is a solid amorphous or a liquid phase. a) Electronic mail: huangyue@ph4.physik.uni-goettingen.de Solid State Phenomena Online: 2003-09-30 ISSN: 1662-9779, Vols. 95-96, pp 617-622 doi:10.4028/www.scientific.net/SSP.95-96.617

Evolution of Hydrogen Related Defects in Plasma Hydrogenated Crystalline Silicon under Thermal and Laser Annealing

Boron doped [100]-oriented Cz Si wafers are hydrogenated with a plasma enhanced chemical vapor deposition setup at a substrate temperature of about 260 °C. In-situ Raman spectroscopy is applied on samples under thermal and laser annealing. It is found that different Si-H species have different stabilities. The most stable one is the Si-H bond at the inner surfaces of the platelets. The dissociated energy of Si-H bonds is deduced based on the first order kinetics. It is found that the hydrogen atoms which are released during annealing are trapped again by the platelets and passivate the silicon dangling bonds at the inner surfaces of the platelets or form H2 molecules in the open platelet volume, possibly relating to the basic mechanism of the hydrogen-induced exfoliation of the silicon wafer and the socalled “smart-cut” process.