Jörg K. N. Lindner

Ion beam synthesis of buried SiC layers in silicon: Basic physical processes

Abstract For the ion beam synthesis (IBS) of buried stoichiometric epitaxial layers of 3C–SiC in silicon, a complicated structure in the as-implanted state has been identified as a favourable starting structure prior to annealing. It consists of a nearly rectangular depth distribution of equally sized, oriented 3C–SiC nanocrystals sandwiched between two amorphous zones. The basic physical processes leading to such a distribution of amorphous and crystalline phases during high-dose, high-temperature carbon implantation into silicon are reviewed in this article. In particular, the precipitation of carbon in a self-organized lattice of amorphous inclusions, the formation of stable 3C–SiC nuclei via precursors, beam-induced nucleation of SiC in amorphous Si:C, the different growth of crystalline SiC precipitates in crystalline and amorphous silicon and the ballistic destruction of SiC nanoclusters by the continued bombardment with energetic ions – resulting in a carbon-induced amorphization at elevated temperatures – are described.

Anti-phase domains in cubic GaN

The existence of anti-phase domains in cubic GaN grown on 3C-SiC/Si (001) substrates by plasma-assisted molecular beam epitaxy is reported. The influence of the 3C-SiC/Si (001) substrate morphology is studied with emphasis on the anti-phase domains (APDs). The GaN nucleation is governed by the APDs of the substrate, resulting in equal plane orientation and the same anti-phase boundaries. The presence of the APDs is independent of the GaN layer thickness. Atomic force microscopy surface analysis indicates lateral growth anisotropy of GaN facets in dependence of the APD orientation. This anisotropy can be linked to Ga and N face types of the {111} planes, similar to observations of anisotropic growth in 3C-SiC. In contrast to 3C-SiC, however, a difference in GaN phase composition for the two types of APDs can be measured by electron backscatter diffraction, μ-Raman and cathodoluminescence spectroscopy.

Structural and morphological investigations of the initial stages in solid source molecular beam epitaxy of SiC on (111)Si

The solid source molecular beam epitaxy is known to allow the lowest process temperatures to grow SiC on silicon. In this work, we investigated the nucleation and the initial SiC growth and propose a growth model in dependence on the supersaturation. At high supersaturation, a smooth continuous layers with large voids in the substrate and especially at low temperatures non-cubic inclusions are formed. At low supersaturations, we found large islands which are separated by deep trenches. Both cases allow an unlimited silicon transport to the surface. In an intermediate range, both types of defects can be reduced.

Ion implantation induced damage in relaxed Si0.75Ge0.25

Abstract The damage produced by implanting, at room temperature, a 3 μm thick relaxed Si 0.75 Ge 0.25 layer with 2 MeV Si + ions has been measured as a function of dose in the range 10 10 –10 15 cm −2 . Depth profiles of the damage have been obtained by both Rutherford Backscattering Spectrometry and Optical Reflectivity Depth Profiling. These measurements show that the levels of damage exceed both those predicted by TRIM and those observed for comparable implantations into Si. Deep Level Transient Spectroscopy of a sample implanted with 10 11 Si cm −2 reveals the presence of both a majority and a minority carrier trap and another minority carrier trap is detected by Minority Carrier Transient Spectroscopy. An Electron Paramagnetic Resonance signal with isotropic g value of 2.011 ± 0.001 is detected in samples implanted with ≥ 3 × 10 13 Si cm −2 and is attributed to both Si and Ge dangling bonds.

Cubic GaN on Nanopatterned 3C-SiC/Si (001) Substrates

In this chapter we demonstrate the growth and characterization of nonpolar relaxed cubic GaN by plasma-assisted molecular beam epitaxy on prepatterned 3C-SiC/Si (001) substrates. Nanopatterning of 3C-SiC/Si (001) was achieved by two different fabrication techniques: nanosphere lithography (NSL) to generate large-area pattern, and conventional electron beam lithography (EBL) for tailoring particular surface morphologies. Both methods were followed by a lift-off and a reactive ion etching (RIE) process. We analyze the influence of the substrate on the GaN growth and show that it is possible to grow single phase and defect-reduced cubic GaN crystals on 3C-SiC nanostructures. Furthermore cubic GaN/AlN multiquantum wells were grown on 3C-SiC nanostructures, which is a further step toward nanoscaled device applications.

Two-dimensional switchable blue phase gratings manufactured by nanosphere lithography

Switchable two dimensional liquid crystal diffraction gratings are promising candidates in beam steering devices, multiplexers and holographic displays. For these areas of applications a high degree of integration in optical systems is much sought-after. In the context of diffraction gratings this means that the angle of diffraction should be rather high, which typically poses a problem as the fabrication of small grating periods is challenging. In this paper, we propose the use of nanosphere lithography (NSL) for the fabrication of two-dimensionally structured electrodes with a periodicity of a few micrometers. NSL is based on the self-assembly of micro- or nanometer sized spheres into monolayers. It allows for easy substrate structuring on wafer scale. The manufactured electrode is combined with a liquid crystalline polymer-stabilized blue phase, which facilitates sub-millisecond electrical switching of the diffraction efficiency at a diffraction angle of 21.4°.

ECR-Ectching of Submicron and Nanometer Sized 3C-SiC(100) Mesa Structures

Anisotropic etching processes for mesa structure formation using fluorinated plasma atmospheres in an electron cyclotron resonance (ECR) plasma etcher were studied on Novasic substrates with 10 µm thick 3C-SiC(100) grown on Si(100). To achieve reasonable etching rates, a special gas inlet system suitable for injecting SF6 into the high density downstream Ar ECR plasma was designed. The influence of the etching mask material on the sidewall morphology was investigated. Masking materials with small grain sizes are preferable to achieve a desired shape. The evolution of the mesa form was investigated in dependence on the gas composition, the applied bias, the pressure and the composition of the gas atmosphere. The achieved sidewall slope was 84.5 deg. The aspect ratios of the fabricated structures in the developed residue free ECR plasma etching process were between 5 and 10. Mesa structures aligned to [100] and [110] directions were fabricated.

Easily Accessible Protein Nanostructures via Enzyme Mediated Addressing

Site-specific formation of nanoscaled protein structures is a challenging task. Most known structuring methods are either complex and hardly upscalable or do not apply to biological matter at all. The presented combination of enzyme mediated autodeposition and nanosphere lithography provides an easy-to-apply approach for the buildup of protein nanostructures over a large scale. The key factor is the tethering of enzyme to the support in designated areas. Those areas are provided via prepatterning of enzymatically active antidots with variable diameters. Enzymatically triggered protein addressing occurs exclusively at the intended areas and continues until the entire active area is coated. After this, the reaction self-terminates. The major advantage of the presented method lies in its easy applicability and upscalability. Large-area structuring of entire support surfaces with features on the nanometer scale is performed efficiently and without the necessity of harsh conditions. These are valuable premises for large-scale applications with potentials in biosensor technology, nanoelectronics, and life sciences.

Heteroepitaxy of III–V Zinc Blende Semiconductors on Nanopatterned Substrates

In the last decade, zinc blende structure III–V semiconductors have been increasingly utilized for the realization of high‐performance optoelectronic applications because of their tunable bandgaps, high carrier mobility and the absence of piezoelectric fields. However, the integration of III–V devices on the Si platform commonly used for CMOS electronic circuits still poses a challenge, due to the large densities of mismatch‐related defects in heteroepitaxial III–V layers grown on planar Si substrates. A promising method to obtain thin III–V layers of high crystalline quality is the growth on nanopatterned substrates. In this approach, defects can be effectively eliminated by elastic lattice relaxation in three dimensions or confined close to the substrate interface by using aspect‐ratio trapping masks. As a result, an etch pit density as low as 3.3 × 10^5 cm^−2 and a flat surface of submicron GaAs layers have been accomplished by growth onto a SiO2 nanohole film patterned Si(001) substrate, where the threading defects are trapped at the SiO2 mask sidewalls. An open issue that remains to be resolved is to gain a better understanding of the interplay between mask shape, growth conditions and formation of coalescence defects during mask overgrowth in order to achieve thin device quality III–V layers

Strain Compensation in Single ZnSe/CdSe Quantum Wells: Analytical Model and Experimental Evidence

The lattice mismatch between CdSe and ZnSe is known to limit the thickness of ZnSe/CdSe quantum wells on GaAs (001) substrates to about 2-3 monolayers. We demonstrate that this thickness can be enhanced significantly by using In0.12Ga0.88As pseudo substrates, which generate alternating tensile and compressive strains in the ZnSe/CdSe/ZnSe layers resulting in an efficient strain compensation. This method enables to design CdSe/ZnSe quantum wells with CdSe thicknesses ranging from 1 to 6 monolayers, covering the whole visible spectrum. The strain compensation effect is investigated by high resolution transmission electron microscopy and supported by molecular statics simulations. The model approach with the supporting experimental measurements is sufficiently general to be also applied to other highly mismatched material combinations for the design of advanced strained heterostructures.