Manufacture and study of ultra-thin films of highly boron-doped single crystal diamond – DeltaDiam

Several groups, either industrial or academic, mainly in Europe, Japan and USA, have recognized and begun to use the huge potentialities of synthetic diamond for implementing electronic devices. If all the electronic, thermal and chemical inertness properties of diamond were simultaneously utilized, unprecedented performances would result. Recent advances in manufacturing and enlarging synthetic crystalline diamond substrates open a practicable route for growing epitaxially all the layers necessary for building electronic devices. The possibility of boron doping from traces close to ppb concentration up to above one percent, offers the opportunity of relying only on diamond for elaborating all the functionalities. The present project proposes that a large density of carriers (here holes) may be brought about by an ultra-thin metallic or nearly metallic buried layer, able to enhance the conductivity of the device at ambient temperature by means of the contiguous undoped diamond layer. The depletion of the channel can be obtained from a perpendicular electric field by means of the gate on the top. Such a field effect transistor has recently been demonstrated by two collaborating groups from England and Germany and prospective researches may exist elsewhere, but a detailed understanding of all the physical mechanisms is lacking. This limits severely the optimization of the design and therefore the device performance. In order to improve the ultimate performances of such devices through reliable predictive tools, we propose to address fundamental issues like the effect of the compressive stress in the 'delta-doped' layer on the band structure, the relevance of the bi-dimensionality on holes transport, the amount of delocalized holes outside the delta-doped layer versus the two-dimensional confinement of the hole gas and its control by the electric field. According to recent literature [E. Kohn, A. Denisenko, Thin Solid Films, 515 (2007) 4333], present state-of-the-art solutions are able to grow nm-thick highly doped boron-doped layers. This is achievable with the microwave plasma enhanced chemical vapor deposition (MPCVD) process, providing a minimization of the active gas residence and switch times in the growth chamber. The aim of the project consists to optimized these aspects with notably the introduction of improved MPCVD different systems at both Institut Néel and LIST . Regarding the specific materials growth aspects, the research effort will be devoted at homogenizing boron doping in "delta-doped" layers together with optimizing the sharpness of doped/undoped interfaces. Thus, technological issues such as the achievement and control of a roughness compatible with the nanometric thickness of the delta-doped and top gate layers, the epitaxial growth of the delta-doped layer itself and the implementation of Schottky and ohmic contacts are all within the field of expertise of the present contractors. Based on the recognized abilities and competences of the set consisting in the three French and one international laboratories participating in this project, all these challenges would be overcome successfully in order to make a real breakthrough towards a new generation of electronic devices, able to work in harsh operating conditions for in terms of microwave power, frequency and operating temperature.