J. Kräußlich

Epitaxial relationship in the AlN/Si(001) heterosystem

The epitaxial growth of crystalline wurtzite AlN thin films on (001) Si substrates by plasma-assisted molecular-beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. Cross-sectional transmission electron microscopy and x-ray diffraction investigations revealed a two-domain film structure (AlN1 and AlN2) with a 30° rotation between neighboring domain orientations and an epitaxial orientation relationship of [0001]AlN∥[001]Si and 〈0110〉AlN1∥〈2110〉AlN2∥[110]Si. A model for the nucleation and growth mechanism of 2H–AlN layers on Si(001) is proposed.

Hexagonal AlN films grown on nominal and off-axis Si(0 0 1) substrates

Nucleation and growth of wurtzite AlN layers on nominal and off-axis Si(0 0 1) substrates by plasma-assisted molecular beam epitaxy is reported. The nucleation and the growth dynamics have been studied in situ by reflection high-energy electron diffraction. For the films grown on the nominal Si(0 0 1) surface, cross-sectional transmission electron microscopy and X-ray diffraction investigations revealed a two-domain film structure (AlN 1 and AlN 2 ) with an epitaxial orientation relationship of [0 0 0 1]AlN || [0 0 1]Si and h 01 %

Growth of atomically smooth AlN films with a 5:4 coincidence interface on Si(111) by MBE

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.

Structural properties of MBE grown Cu(In,Ga)S2 layers on Si

Abstract The epitaxial growth of the quaternary CuIn (1− x ) Ga x S 2 system with 0≤ x ≤1 on silicon substrates is investigated. Using molecular beam epitaxy, the layers were deposited on sulphur-terminated Si at a substrate temperature of typically 820 K. Reflection high-energy electron diffraction, Rutherford backscattering, X-ray diffraction, and transmission electron microscopy are employed to gain insight into the structural properties of the epitaxial layers with an emphasis on the interplay of lattice mismatch and cation sublattice ordering. All compounds grow epitaxially on Si(111). The quaternary films show a coexistence of chalcopyrite and metastable CuAu-type cation ordering. Lattice match to Si is found for gallium atomic fractions of x =0.41(2).

MBE-growth of heteropolytypic low-dimensional structures of SiC

The controlled growth of SiC heteropolytypic structures consisting of hexagonal (α-) and cubic (3C-) polytypes has been performed by solid-source molecular beam epitaxy. On on-axis substrates, 4H/3C/4H-SiC(0001) and 6H/3C/6H-SiC(0001) structures were obtained by first growing some nanometers thick 3C-SiC layer at lower temperatures (1550 K) and Si-rich conditions, and subsequent growth of α-SiC on top of the 3C-SiC layer at higher temperatures (1600 K) under more C-rich conditions. On off-axis substrates, multi-heterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively wire-like 3C-SiC nuclei on the terraces of well-prepared off-axis α-SiC(0001) substrates at low T (< 1500 K). Next, SiC was grown further in a step-flow growth mode at higher T and Si-rich condition. After the growth many wire-like regions consisting of 3C-SiC were found within the hexagonal SiC layer material matrix indicating a simultaneous step-flow growth of both the cubic and the hexagonal SiC material.

Microstructure of epitaxial CuGaS2 on Si(111)

Abstract CuGaS 2 has been grown epitaxially on Si(111) substrates by three-source molecular beam epitaxy. The structural properties of these layers have been investigated by means of X-ray diffraction, high-resolution electron microscopy, and selected-area electron diffraction. It is found that CuGaS 2 crystallizes exclusively in the chalcopyrite structure. The interface region exhibits a strong tendency to form stacking faults. The epitaxial growth is characterized and it is shown that the epilayers compensate the lattice mismatch to the Si substrates by means of a small tilt of about 0.8° between the CuGaS 2 〈221〉 directions and the [111] surface normal of the Si substrate.

Epitaxial growth of SiC-heterostructures on α-SiC(0001) by solid-source MBE

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.