Sharp interfaces for diamond delta-doping and SIMS profile modelling

Boron delta-doping of diamond has appeared as a promising viable approach for the fabrication of high performance RF power transistors taking advantage of diamond properties. Here structures based on p−/p+/p− multilayers were synthesized on (100) HPHT Ib substrates using MPCVD. An original gas injector system was developed enabling to significantly improve the sharpness of both interfaces between p+ and p− layers with a good reproducibility. SIMS profiles recorded on the doping transients still demonstrate an asymmetry of the interface sharpness from 7 nm/decade to 2 nm/dec on the p−/p+ and the p+/p− interfaces, respectively. The observed differences are here explained and confirmed experimentally, and result from the combination of ion mixing with the effect of the surface roughness, thus limiting the SIMS resolution in depth. The Mixing Roughness Information (MRI) model then allows to evaluate the real value of the delta thickness achievable using this technique to 7 nm and the negative and positive gradients to identical values, namely of 1.4 nm/dec.