Growth and characterization of diamond delta-doped layers for FET applications

Abstract

In this work, a special growth technique for "Delta-Doped Layers" was developed and analyzed in details. The accuracy as well as the reproducibility of this growth technique have been demonstrated. These delta layers were afterward characterized using many different methods. The electrical measurement showed that these layers have a sheet resistance in the range of 5-9 KOmega/square, with full activation of the boron at room temperature, which makes them very convenient to be used as FET channels. They also show a very low surface roughness, with smoothness values in the range of 0.3 nm (RMS). The carrier profile was also analyzed using capacitance-voltage measurements, with metal contacts as well as in the liquid, and the carrier profiles showed a maximum concentration in the range of 1×10^20 cm^-3 to 6×10^20 cm^-3, which results in a sheet carrier concentration of 1-3×10^13cm^-2. These results also agree with the physical/chemical analysis methods (SIMS, ERD). Using these delta layers either as a channel, we were able to design P-I-P FET, single delta FET and double delta FET structures. Such FET structures, using a boron delta doped channel has been realized for the first time, which enables both full channel modulation with complete pinch-off and full room temperature carrier activation. Also, first RF data have been obtained and cut-off frequencies in the lower GHz-range could be extracted. Despite a gate recess, the devices have still been plagued by parasitic series resistances and a gate dielectric of Al2O3 had to be inserted to control the gate leakage. Nevertheless, current levels had still been low due to the low channel carrier mobility. Especially this last point indicates that the delta doping technology needs still further refinement to obtain acceptor doping profiles, which are essentially steeper than the corresponding Debye tail to take advantage of a 2D-channel mobility enhancement, the ultimate goal being monolayer planar doping.