  In this study the MOCVD growth and electrical properties of N-polar
modulation doped p-AlGaN/GaN superlattices (SLs) were investigated. Hole sheet
charge density and mobility were studied as a function of the concentration of
the p-type dopant Mg in the SL and the number of SL periods. Room temperature
Hall measurements were carried out to determine the hole mobility and the sheet
charge density. While the hole density increased with increasing number of SL
periods, the hole mobility was largely unaffected.Hole mobilities as high as
18cm2/Vs at a simultaneous high hole density of 6.5e13 cm-2 were observed for
N-polar SLs with a Mg modulation doping of 7.5e18 cm-3. For comparable
uniformly doped Ga-polar SL samples, a mobility of 11cm2/Vs was measured.
Lowest sheet resistance in the GaN/AlGaN materials system of 5kOhm/sq is also
reported. Test-structure transistors were also fabricated to investigate the
applicability of these SL structures, with planar device resulting in a current
of 5mA/mm, and a FinFET structure resulting in a current of over 100mA/mm.
