International audienceDefects induced by boron doping in diamond layers were studied by transmission electron microscopy. The existence of a critical boron doping level above which defects are generated is reported. This level is found to be dependent on the CH 4 /H 2 molar ratios and on growth directions. The critical boron concentration lied in the 6.5–17.0 10 20 at/cm 3 range in the <111> direction and at 3.2 10 21 at/cm 3 for the <001> one. Strain related effects induced by the doping are shown not to be responsible. From the location of dislocations and their Burger vectors, a model is proposed, together with their generation mechanism
Progress in power electronic devices is currently accepted through the use of wide bandgap materials (WBG). Among them, diamond is the material with the most promising characteristics in terms of breakdown voltage, on-resistance, thermal conductance, or carrier mobility. However, it is also the one with the greatest difficulties in carrying out the device technology as a result of its very high mechanical hardness and smaller size of substrates. As a result, diamond is still not considered a reference material for power electronic devices despite its superior Baliga’s figure of merit with respect to other WBG materials. This review paper will give a brief overview of some scientific and technological aspects related to the current state of the main diamond technology aspects. It will report the recent key issues related to crystal growth, characterization techniques, and, in particular, the importance of surface states aspects, fabrication processes, and device fabrication. Finally, the advantages and disadvantages of diamond devices with respect to other WBG materials are also discussed.
International audienceThe selective doped overgrowth of 3D mesa patterns and trenches has become an essential fabrication step of advanced monolithic diamond-based power devices. A novel methodology is proposed here, combining the overgrowth of plasma-etched cylindrical mesa structures with the sequential growth of doping superlattices. The latter involve thin heavily boron doped epilayers separating thicker undoped epilayers in a periodic fashion. Beside the classical shape analysis under the scanning electron microscope relying on the appearance of facets corresponding to the main crystallographic directions and their evolution toward slow growing facets, the doping superlattices were used as markers in oriented cross-sectional lamellas prepared by Focused Ion Beam and observed by Transmission Electron Microscopy. This stratigraphic approach is shown here to be applicable to overgrown structures where faceting was not detectable. Intermediate growth directions were detected at different times of the growth process and the periodicity of the superlattice allowed to calculate the growth rates and parameters, providing an original insight into the planarization mechanism. Different configurations of the growth front were obtained for different sample orientations, illustrating the anisotropy of the 3D growth. Dislocations were also observed along the lateral growth fronts with two types of Burger vector: bsub01-1 = 1/2 [01-1] and bsub112 = 1/6 [112]. Moreover, the clustering of these extended defects in specific regions of the overgrowth prompted a proposal of two different dislocation generation mechanisms
International audienceSelective diamond growth on etched diamond substrates allows the developement of 3D-type device geometries, which can make possible higher capacity, higher surface for contacts and benefits from better properties versus growth orientation. Such structures need the control of lateral growth and lateral etching that garantee the best epitaxial growth, with a well-faceted surface, with a minimum density of emerging defects in order to limit the current leakage and to improve the breakdown voltage. Previous works used 111-oriented selective growth on etched diamond for lateral p-n junctions or bipolar junction transistors. The behavior of homepitaxial overgrowth on etched diamond substrates depends directly on growth parameters such as temperature, gas concentration or microwave power that can favor the growth in one specific direction. The present contribution considers the effect of methane concentration during the overgrowth of the mesa pattern. The presence of highly doped intermediate layers allowed following the growth plane orientation in a stratigraphic approach. Faceting and growth velocities were analyzed using scanning and transmission electron microscopes (SEM and TEM)
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