Optimization of conductivity in p-type GaN∕InGaN-graded superlattices

Carrier transport simulations show that significantly improved vertical and lateral electrical conductivity (σV and σL) can be achieved in p-type GaN∕InGaN superlattices utilizing composition-graded p-InGaN layers. Compared to typical modulation-doped superlattices, the barrier height and the sheet-hole density in the p-InGaN wells were, respectively, more than eight times lower and 2.6 times higher. This achievement is due to the combination of a number of factors, including polarization charge distribution in the graded layers, an adjusted Mg-doping profile, and a shallower acceptor activation energy in InGaN. The optimized superlattice design leads to an improvement of more than eleven orders of magnitude in σV compared to typical superlattices while maintaining a value for σL that is better than that of bulk p-InGaN. Both σV and σL are found to improve at higher temperatures in the optimized structure.

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