Trade-off for optimizing drift region of diamond power devices
Résumé
Diamond with its high critical electric field, opens the way to very high voltage power components. Diamond Schottky diodes and transistors has been demonstrated but do not show performances as high as expected. In fact, a particular attention has to be paid to the design of the drift layer to take benefit of the diamond superlative properties. The drift region thickness and doping level must be chosen to optimize the ON state resistance for any breakdown voltage (OFF state). A focus on the optimization of the Ron.S(BV) figure of merit has been carried out, while optimizing the drift layer. Based on the ionization integral calculation with impact ionization coefficients adapted to diamond, we performed an accurate analysis of the reciprocal punch through factor as function of the breakdown voltage to propose the drift layer architecture offering the best performances. We will show how performances of experimental devices from literature could have been drastically improved using this optimum design: Ron.S divided by 20 in certain cases. Nevertheless, our analysis points out that thicknesses and doping levels required to achieve the optimum drift layer are challenging for crystal growth, especially for high breakdown voltage. Thus, it is not always possible to use this optimum design for some technological reasons or due to component specificities and therefore further tradeoffs has to be done. For instance, we proposed a specific doping profile for Schottky diode that helps to maintain a low leakage current level without slashing the on state performances. An additional two dimensional cylindrical coordinate analysis was performed to quantify the radius effect on the breakdown voltage value for different drift region designs.