Ohmic and rectifying contacts on bulk AlN for radiation detector applications

In this paper we report on ohmic and rectifying contacts fabricated on undoped bulk AlN substrates for radiation detector applications. The ohmic Ni contacts exhibit negligible contact resistances. Current conduction is dominated by field enhanced thermal emission from traps 0.4 to 0.6 eV below the conduction band. The Pt Schottky contacts show excellent rectifying behaviour. In forward conduction, device current is again limited by the Poole-Frenkel effect. The Schottky barrier features very low reverse leakage currents, and voltages of up to -200 V can be applied. The capability of bulk AlN for radiation detectors at room temperature is demonstrated. Suitability is deduced from both X-ray absorption experiments and low reverse leakage currents of the fabricated Schottky diodes. Additionally, the AlN substrate is almost blind to sun light due to its wide band gap. Still, reduction of recombination sites in AlN is required to achieve maximum detector performance.