Fermi-level depinning at metal/GaN interface by an insulating barrier

We have investigated Schottky contacts on GaN and observed that Fermi level pinning is dominant at the metal/GaN interface with a pinning factor of 0.23. A methodology to solve the problem by introducing a thin layer of MgO between the metal and the semiconductor is demonstrated here. It is observed that the insertion of a thin layer of the insulator prevents the metal wave-function penetration into the semiconductor band gap which in turn helps in the Fermi level depinning for GaN. We have particularly demonstrated the Fermi level depinning for ferromagnetic Schottky contact Fe and shown its usefulness for electrical spin injection and detection. The resistance-area product of an as deposited Fe/GaN contact is found to be too high for efficient spin injection and detection. It is improved considerably by using a 3 nm layer of MgO and the effective barrier height is reduced to 0.4 eV. We have further investigated the influence of low work function metal Gd and found it is possible to do barrier height engineering when deposited in conjunction with other metals.