Highly resistive GaN layers formed by ion implantation of Zn along the c axis

Abstract

Highly resistive layers are formed by the implantation of Zn ion along the c axis of GaN and AlGaN/GaN epitaxial layers. Heavy ions such as Zn have been desirable for the formation of highly resistive layers, because ions effectively transferred their energy to the crystal atoms rather than the electrons in GaN. A sheet resistance Rs as high as 3.8×1011 Ω/sq was obtained on GaN layers after the ion implantation. Rs increased up to 2.2×1013 Ω/sq after the annealing at 500 °C for 300 s in an N2 atmosphere. The thermal activation energy Er for this sample was 0.67 eV. It was found that the experimental data in current–voltage characteristics were fitted to the equation included the Poole–Frenkel current and resistive (ohmic) current. The difference of Rs between the as-implanted and 500 °C annealed samples was due to the Poole–Frenkel current. The Poole–Frenkel current overcame the resistive one, and dominated the current mechanism in the case of the samples annealed at 200 °C or less. On the other hand, for the samples annealed at 500 °C, the current was only resistive. Both Rs and Er decreased as the annealing temperature increased above 500 °C. Furthermore this implantation method was applied to the device isolation of AlGaN/GaN high electron mobility transistors (HEMTs). The high Rs of 5.9×1011 Ω/sq was observed for AlGaN/GaN structures as well as GaN layers which were not annealed. The HEMTs with a gate length of 1 μm had a high drain current of over 1 A/mm at the gate voltage of 1 V and a pinch off voltage of −7 V without a harmful leakage current.