INTRODUCTION

The AAPPLES Network, which is one of the first group of Networks started under the TMR Programme, is the logical successor of an earlier Network launched under the HCM Programme (Low Thermal Budget Epitaxy of Si and Si Alloys; Contract No. ERBCHRXCT 930213). This first Network was aimed at the development of low thermal budget deposition techniques for epitaxial Si and Si_1-xGe_x materials. In AApples, these deposition techniques are explored further and used for advanced applications in micro-electronics. In the field of micro-electronics, Si occupies a unique position, being the absolutely predominant material for the manufacturing of electrical devices in many different applications, going from Bipolar to CMOS, from analog to digital, covering low power consumption and high frequencies. Two applications have been out of the scope of Si for many years: very high speed and opto-electronical applications (light emitters and receivers, detectors). This was the exclusive domain of the III-V's, GaAs and its related materials, thanks to their special bandgap characteristics and the possibilities for engineering these bandgaps by combining many slightly different alloy compositions. Since the researchers learned how to make Si_1-xGe_x alloys in thin, pseudo-morphic epitaxial layers, also these techniques have become available to the Si device engineers, and a whole suite of Si_1-xGe_x devices has shown up since that moment. AApples has to be situated in this field of research and developments.

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