Johannes Völkl

First results on silicon carbide vapour phase epitaxy growth in a new type of vertical low pressure chemical vapour deposition reactor

In this paper a new concept for silicon carbide vapour phase epitaxy (VPE) will be presented. It is based on the rotating disk technology well known in the field of III–V epitaxy. First results will be given showing excellent structural quality of the epitaxial layers together with high growth rates up to 5 μm/h and good uniformity of layer thickness over 1 inch wafers. The CSi-ratio in the process can be varied over a wide range (0.35-2.3 at 3 μm/h) without loss of surface quality. This enables a precise control of the site competition effect and, therefore, of the incorporation of acceptor and donor impurities. Thus, non-intentionally doped p- (CSi > 1) and n-type (CSi < 0.7) epilayers with carrier concentrations considerably below 1016 cm−3 can be grown.

The plasticity of GaAs between 415 and 730°C

Abstract GaAs single crystals grown by the liquid-encapsulated Czochralski method are compressed along ‘123’ under a protective atmosphere of flowing Ar. The resulting stress-strain curves, which are rather similar to those observed in other III-V compounds, are analysed according to the beginning of plastic deformation and to dynamical recovery. The lower yield point is characterized by an activation energy of l·24eV and a stress exponent of 3·5. Both values compare favourably with those obtained from measurements of the dislocation velocity. From the strain-rate and temperature dependence of the stress τIII at the onset of the first recovery stage, an activation energy of approximately 2eV is derived, which may be regarded as a lower bound for the activation energy of self-diffusion of the slowest-moving species. Comparing these results with those obtained for other semiconductors corroborates a view increasingly supported in the literature, namely that moving dislocations emit or absorb point effects.

The yield point of In‐doped GaAs between 500 and 900 °C

In‐doped (5×1019/cm3) GaAs single crystals with 〈123〉 orientation are compressed at different strain rates and temperatures between 500 and 900 °C. Two different regimes are observed. At high strain rates and temperatures below 700 °C, the strain‐rate dependence of the lower yield stress is characterized by a power law with a stress exponent of 3.7, while its temperature dependence obeys an Arrhenius law with an activation energy of 0.93 eV. The latter value is smaller than that found for undoped GaAs, but the stress exponent is practically unchanged. This regime is interpreted in terms of a kink mechanism; the rate‐controlling process is assumed to be governed by a strong interaction of In atoms with α dislocations. The regime occurring at low strain rates and temperatures above 700 °C is characterized by strong hardening and a weak temperature and strain‐rate dependence of the lower yield stress. This behavior is ascribed to a direct alloying effect. Different types of interaction between dislocations a...

Silicon Carbide Cvd Approaches Industrial Needs

In this paper an overview is given on the current state of epitaxial growth of SiC with special regard to our work at SIEMENS CRD. Problems concerning impurity incorporation and ways to achieve background doping levels as low as 10 14 cm −3 are discussed as well as the influence of high speed wafer rotation on the gas flow in our reactor and related effects on uniformity in thickness and doping. Precise control of the C/Si ratio in the gas phase, which is easily achieved in the described reactor, and the use of reduced pressure lead to a good control of dopant incorporation over more than 3 orders of magnitude while maintaining smooth surface morphology even at growth rates higher than 5 μm/h. Doping variations * 10 6 V/cm at N A −N D =5 * 10 −15 cm − and an electron mobility greater than 700 cm 2 /Vs at 300 K (4H-SiC). Finally it is demonstrated that the gas composition at the end of the epitaxial growth process is an important step in order to get oxygen resistant surface properties for subsequent device processing.