Low-resistivity Mg-doped Al/sub 0.15/Ga/sub 0.85/N/GaN strained-layer superlattices were grown. In these superlattices, the maximum hole concentration is 3/spl times/10/sup 18//cm/sup 3/ at room temperature. Hall-effect measurements indicate high conductivity of this structure in which the high activation efficiency is attributed to the strain-induced piezoelectric fields. This work also fabricated InGaN/GaN blue LEDs that consist of a Mg-doped Al/sub 0.15/Ga/sub 0.85/N/GaN SLs. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 3 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V.