Vertical conductivity and Poole-Frenkel-ionization of Mg acceptors in AlGaN short-period superlattices with high Al mole fraction

Abstract

Mg-doped AlGaN short-period superlattices with a high aluminum mole fraction are promising to fabricate highly efficient deep UV light emitting diodes. We present a robust and easy-to-implement experimental method for quantification of the vertical component of the anisotropic short-period superlattice conductivity based on current-voltage characteristics of devices with varying short-period superlattice thicknesses. In particular, the vertical conductivity of Al0.71Ga0.29N/Al0.65Ga0.35N:Mg short-period superlattices is investigated and found to be strongly affected by the temperature and by the applied electric field. At room temperature, the vertical conductivity varies between 5.5 × 10-7 ω -1 cm-1 at 0.05 MV cm-1 and 6.7 × 10-5 ω-1 cm-1 at 0.98 MV cm-1 and increases by almost two orders of magnitude when the temperature increases up to 100 °C. This behavior is in very good agreement with simulations based on a 3D-Poole-Frenkel model. In addition, the zero-field ionization energy and the inter-trap distance of the Mg acceptors in the AlGaN short-period superlattices were determined to be 510 ± 20 meV and 5.1 ± 0.3 nm, respectively.