Enhanced vertical transport in p-type AlGaN∕GaN superlattices

We report on p-type AlGaN∕GaN superlattice designs with significantly improved vertical and lateral electrical conductivities (σV and σL). Composition-graded p-AlGaN layers produce a polarization charge distribution, which together with an appropriate Mg doping in the structure leads to more than an eightfold reduction of barrier height and a ∼50% increase in the sheet hole density in the p-GaN wells compared to typical modulation-doped superlattice structures. Using the optimized structure, more than 13 orders of magnitude and 35 times improvement is shown for σV, compared to typical superlattice and σL, compared to bulk p-GaN, respectively. Both σV and σL are found to improve significantly at higher temperatures in the optimized structure.

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