Impact of defects on the electrical properties of p–n diodes formed by implanting Mg and H ions into N-polar GaN

Abstract

The relationship between the junction properties and point defects in p–n diodes, formed by implanting magnesium (Mg) and hydrogen (H) ions into a GaN layer, was investigated. Vertical diodes were fabricated by implanting Mg ions with and without H ions into nitrogen-polar n-type GaN substrates, followed by annealing at 1150 °C or 1230 °C without the use of protective layers. Samples annealed at 1150 °C showed Schottky-barrier-diode (SBD)-like properties with an insufficient build-in potential, indicating surface depletion due to poor activation of Mg acceptors. The Mg/H-ion-implanted diode annealed at 1230 °C exhibited an improved rectifying property with a build-in potential around 3 V, close to an ideal p–n junction of GaN, whereas the sample with only implanted Mg-ions exhibited mixed properties of a p–n junction and SBD due to imperfect activation. In addition, leakage currents in the forward bias below 3 V for the Mg/H-ion-implanted diodes can be explained by a recombination current based on the Shockley–Read–Hall model with an estimated recombination lifetime of 3 to 10 ps. To clarify the sources of the difference in the junction properties, positron annihilation spectroscopy was employed. The samples annealed at 1150 °C contained high-density vacancy clusters such as (VGaVN)3, whose concentrations were reduced by the higher temperature annealing. We found that introduced H atoms can enhance the activation of Mg acceptors and/or reduce the defect concentrations. The results indicate the combination of the H ion introduction and higher temperature annealing improves the junction properties.