High Lateral Breakdown Field in Ib HPHT Diamond Substrates

The efficiency of power devices is critical nowadays for the rise of renewable energy. A great effort is being put into trying to optimize both energy dissipation and blocking capability. In the latter respect the goal is to increase as much as possible the voltage breakdown of devices in the off-state. Because the breakdown voltage increases with the semiconductor bandgap, Ib HPHT diamond substrate, with a bandgap of 5.5 eV, is a candidate as the ultimate substrate for power devices. In particular Ib HPHT diamond substrates are widely used for lateral Field Effect Transistors (FET) thanks to its insulating properties at room temperature.<br/>In this work, the blocking characteristics of diamond Ib nitrogen-doped substrates are investigated through the use of metallic contacts separated by different gap widths in order to apply large range of electric field (from V/cm to MV/cm). Thanks to the electron beam lithography technique, several metallic structures separated by different gaps down to 500 nm were deposited on an Ib HPHT diamond substrate. The I-V characteristics between two electrodes have been measured up to reach the breakdown voltage of each structures. In order to understand the breakdown mechanism underlying within the structure, electron beam induced current (EBIC) has been used in order to map the electric field between two successive electrodes. This experiment is particularly useful for voltages close to the breakdown voltage.<br/>In the first part of this presentation, the method will be described in details. Then, the I-V characteristics for different breakdown voltages and fields up to 10 MV/cm will be reported and compared with previous theoretical and experimental results. Finally, the mechanism causing the breakdown of the material will be discussed and compared with finite element simulation.