Surface transfer-doping, involving hydrogen terminated diamond surfaces, has been an effective method for producing diamond devices for some years but suffered from poor device longevity and reproducibility. The emergence of metal oxides as an encapsulant has begun to change this situation. Here, HfO2 encapsulated surface transfer doped diamond Schottky diodes with stable device characteristics have been demonstrated. Ideality factor and Schottky barrier heights of the devices did not vary considerably across extended periods of use (up to 39 days). The devices showed excellent blocking capabilities, demonstrating no catastrophic breakdown under the maximum field applied and only a slight increase in leakage current at the reverse bias and field strength of 200 V and 0.167 MV cm−1
, respectively. Indeed, a large rectification ratio of up to 108 and a very low leakage current of ≈10−9 A cm−1
were maintained at this reverse bias (200 V). Furthermore, multiple devices were compared across a single substrate, something rarely reported previously for surface transfer doped diamond diodes. Leakage currents and rectification ratios were similar for all of the devices.
The authors are grateful to the UKs Engineering and Physical Sciences Research Council (EPSRC) and BAE Systems Marine Ltd. for the award of a “Cooperative Awards in Science and Engineering (CASE)” Ph.D. Studentship for R.J.W. and to EPSRC for the award of related research funding (No. EP/H020055/1). A.C.P.-T. and R.B.J. also acknowledge invaluable assistance, both financial and in the form of international collaborations, from the European Commission Horizon 2020 Project “GREENDIAMOND” (H2020 Large Project under Grant No. SEP-210184415). Lambda Photometrics Ltd. and Everbeing International Corporation are gratefully acknowledged for use of a Everbeing EB-6 DC probe station. Finally, the LCN Cleanroom is acknowledged for the invaluable assistance of technicians and for the use of the ALD, evaporation, and photo-lithography tools
