<title>Characterization of MPCVD diamond films grown on porous silicon</title>

Abstract

Spectrally and temporally resolved cathodoluminescence (CL), micro-Raman spectroscopy and the investigation with a scanning force microscopy in a contact current mode (CCM-SFM) are used for characterizing the properties of diamond films. The diamond films and particles are grown by microwave plasma-assisted CVD (MPCVD) on top of monocrystalline and porous silicon (PS) surfaces. The PS layers with different thicknesses and porosity are formed on (111) and (100) silicon by anodization in 12 percent HF solution (HF : H<SUB>2</SUB>O equals 1 : 3) at constant current density. A 15 keV electron-beam is used for CL excitation. The CL investigations are carried out at 77 K using an optical multichannel analysis system with simultaneous resolutions of (Delta) (lambda) equals0.2 nm and (Delta) tequals1 ns. Complementary Raman analysis has shown that the synthesized films exhibit diamond structure with good crystalline quality. Diamond films on monocrystalline silicon mostly yield a Raman peak shift of 3-5 cm<SUP>-1</SUP> towards higher wave numbers compared to those of natural diamond due to the presence of compressive stress. The presence of PS allows to reduce stress in diamond films up to a peak shift of 1-2 cm<SUP>-1</SUP> under the same deposition conditions. Intensity and FWHM of the cathodoluminescence as well as the FWHM of the Raman spectrum on PS decrease compared to those of silicon. This indicates that PS is superior to monocrystalline silicon concerning the crystalline quality of the diamond films. High- lateral-resolution analysis, in order to correlate the surface topography with the electrical properties of these diamond films, is carried out by a CCM-SFM. From these characterization methods crucial material system parameters are deduced revealing the influence of a thin PS layer on the crystalline and electrical properties of the diamond films grown on top.