Highly Conductive and 260 nm Transparent p-Type Al0.6Ga0.4N Achieved Utilizing Interface Doping Effects

Abstract

Achieving highly conductive p-type AlGaN with an absorption edge below 260 nm still remains a challenge. In this work, Mg-doped AlxGa1–xN (x ∼ 0.6) layers were grown by taking advantage of interface doping effects. The doping interface was proposed to be divided into lower and upper interfaces, in which the lower one is energetically favorable for Mg substituting Al, while the upper one is favorable for Mg substituting Ga. Accordingly, metal-source pulse flows were introduced to promote the interface effects. It was found that Mg incorporation was significantly enhanced by the two interface effects. The activation energy of a Mg acceptor was also substantially reduced (∼89.6 meV), benefitting from the enhanced Al composition modulation by the Al-source pulse flow. Also, oxygen donors were suppressed in the Al-enriched interface condition. A maximum hole concentration of 1.52 × 1018 cm–3 and mobility of 0.57 cm2/(V·s) were therefore obtained, resulting in a record low resistivity of 6.94 Ω·cm. The p-type layer showed a transmittance greater than 90% at wavelengths above 260 nm. These results indicate that utilizing the interface doping effects is a convenient and effective way for achieving high conductivity not only in Al-rich p-AlGaN but also in other semiconductors.