Enhanced Hole Transport in Mg-Doped AlxGa1-xN/GaN Superlattices by Strain and Period Modulations

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This is a report on parallel and perpendicular hole transport characteristics of Mg-doped AlxGa1-xN/GaN superlattices (SLs). For parallel transport, the sheet resistance of SLs was dramatically decreased by a factor of 7, from 15.2 to 2.20 k\Omega/\square, when an AlN interlayer was inserted to reduce tensile strains. By optimizing the periods of SLs, we have further achieved a better value of 1.68 k\Omega/\square. For perpendicular transport, the vertical conductivity of SLs was also improved from 1.91\times 10^{-5} to 3.76\times 10^{-4} \Omega^{-1} cm-1 by reducing the tensile strains. However, this vertical conductivity improvement deteriorated, when the periods outside optimum or medium boundaries as illustrated in the experimental results. These results indicate that strain and period modulations can have a great impact on the conductive properties of SLs. Meantime, less tensile strains or medium periods can favor the enhancement of hole transports in SLs.
2012-07-25