Search

The self-organized growth of Ge islands on various hexagonal SiC{0001 surfaces is discussed. The formation of two (2-D) or three-dimensional (3-D) Ge islands depend on the polarity of the SiC substrate (silicon or carbon face), the SiC surface stoichiometry and reconstruction, the growth rate and temperature. Furthermore, the nucleation conditions can be modified by an oxidation of the Si-adlayer present on Si-rich SiC surfaces. On the Si face of SiC(0001)-(√3 × √3)R30°, 2-D Ge islands of lateral dimensions between 2 and 4 nm and a density of more than 10 12 cm - 2 are initially formed on a 0.3 nm thick Ge wetting layer. Similar to Si substrates, a further growth leads to the formation of equilibrium 3-D Ge nanocrystals of typically more than 20 nm in size and a density of about 10 10 cm 2 . A Ge deposition on the C face of SiC, as well as on the oxidized Si adlayer of a Si face of SiC results in small 3-D Ge islands of only a few nanometers in size and a number density between 10 and 10 12 cm -2 .

The influence of heavily-doped substrates on the homoepitaxial growth kinetics of Si on Si(111) is studied in real time by means of reflection high-energy electron diffraction as function of temperature and growth rate. The growth experiments were performed by means of molecular beam epitaxy. The obtained results were compared with the growth kinetics on undoped substrates within the framework of nucleation theory. It was found that in comparison with undoped Si(111), the nucleus density in the case of Si(111):P is significantly increased at the same growth conditions that can be attributed to a longer lifetime of the smallest stable islands consisting of a Si pair on the Si(111):P surface. It can be concluded, therefore, that phosphorus is always present on the growing surface during high-temperature preparation of heavily P-doped Si(111). There, the phosphorus atoms saturate dangling bonds at the island edges. For further island growth, phosphorus atoms have to be displayed before silicon adatoms can be incorporated into the island edges, demanding an additional energy. In this sense, phosphorus acts as a surfactant.

Epitaxial growth of SiC on α-SiC(0001) has been performed by means of solid-source molecular beam epitaxy (MBE). Low temperature (T 1200°C, with a step decrease of supersaturation, a step-flow growth mode and for the first time nucleation of both 4H- and 6H-SiC under C-rich conditions was obtained. Based on these results we have demonstrated the growth of a double-heterostructure by firstly growing a 3C-SiC film on 4H-SiC(0001) at low temperature and a subsequent growth of 4H-SiC at low supersaturation on a C-stabilized surface on top of this film. Moreover, we also propose a new model to explain quantitatively the occurrence of different growth features and polytypes under certain growth conditions.

3C–SiC thin films have been investigated by means of high resolution X-ray diffraction techniques ( ω /2Θ-scan, ω- scan) and X-ray topography. The SiC films were grown in a solid source molecular beam epitaxy (MBE) system on 6H–SiC substrate crystals. We investigate the lattice mismatch parallel and perpendicular to the [0001]-direction using the so-called reciprocal space mapping technique. When 3C–SiC films were grown on 6H–SiC substrates, double position boundaries (stacking sequence ACB instead of ABC) were frequently observed. For the visualization of this effect high resolution X-ray topographic measurements are investigated at 3C–SiC layers on 6H–SiC substrates. We find, that the domains of different stacking sequences are equally distributed in the 3C–SiC epilayer. This domains attain a size up to approximately 200×200 μm 2 .

Epitaxial aluminum nitride AlN(0001) thin films have been grown by plasma-assisted molecular beam epitaxy (PA-MBE) on Si(111). The influence of the composition of the nitrogen plasma on the crystal quality, as judged by X-ray diffractometry (XRD) and atomic force microscopy (AFM), has been investigated. Under an Al/N vapor phase ratio close to unity atomically smooth AIN films have been grown at 850°C substrate temperature with maximum growth rates of 2.5 nm min - 1 . A √3 × √3 and a more Al-rich 2 × 6-surface reconstruction have been observed. Transmission electron microscopy (TEM) investigations show that these films are homogeneous 2H-AIN single crystals. Their defect structure consists of threading dislocations mostly. The hetero-interface is abrupt and flat. Processed high-resolution (HR) TEM images demonstrate a 4×d Si(T10) to 5 × d AlN(2110) coincidence between substrate and epilayer. The XRD FWHM of the (0002)-diffraction peak of 0.5 μm AIN is 0.06° in the ω/2 scan and 0.32° in the ω scan. Phonon modes of AIN have been detected by Raman and infra-red spectroscopy.

Thin crystalline SiC films were grown on Si(111) using solid state evaporation at substrate temperatures between 780 and 900 °C. The growth rates were in the range between 30 and 120 nm h−1. The films were characterized by in situ reflection high-energy electron diffraction (RHEED) and ex situ transmission electron microscopy (TEM), scanning electron microscopy (SEM), infrared (IR) spectroscopy and X-ray diffraction (XRD). The films grown at high temperatures and low growth rates were found to be epitaxial. They mostly consist of twinned-cubic structure, but with increasing layer thickness hexagonal stacking sequences often were found. In the orientation distribution function full width at half maximum (FWHM) values of down to 1° were measured.