Diamond power devices. Concepts and limits

The prospects and limits of diamond power devices incorporating boron as dopant are discussed using the results of a theoretical/empirical analysis coupled to 2D-numerical simulation. To obtain full activation of the boron acceptor at room temperature, the concept of delta-doping is introduced and used as basic element. Two device concepts were chosen for this analysis: (i) RF power FET incorporating a monolayer boron delta-doped channel and gate recess and gate filed plate structure; and (ii) various types of vertical power diodes including a novel stacked delta-doped structure, which is proposed here for the first time. The analysis was performed considering the limiting material parameters known for single crystal diamond including recent data on the carrier mobility, the phenomena related to thermal activation of boron acceptor and carrier scattering along and across delta-doped layers, thermal and electrical breakdown limits. The results of this study reveal that the optimised delta-FET with the field plate of 1 μm may be capable to produce approximately 34 W/mm continues-wave RF power at 20 °C operation temperature. The projected RF power of a similar FET structure with the field plate of 2 μm is about 75 W/mm, which may be beyond the thermal limit. The proposed stacked delta-doped diode could have the best on-resistance to blocking voltage ratio than any other type of diamond and n-type SiC-based diodes up to 20 kV blocking voltage. Below 3 kV the projected characteristics of the stacked delta diode on diamond are also favourable in comparison to those of an ideal n-type GaN diode. These examples demonstrate that boron delta-doped layer is a very promising configuration for various diamond-based power electronic devices.