Investigation of nitrogen polar p-type doped GaN/AlxGa(1-x)N superlattices for applications in wide-bandgap p-type field effect transistors

Abstract

In this study, the metal-organic chemical vapor deposition 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 the increasing number of SL periods, the hole mobility was largely unaffected. Hole mobilities as high as 18 cm2/V s at a simultaneously high hole density of 6.5 × 1013 cm-2 were observed for N-polar SLs with a Mg modulation doping of 7.5 × 1018 cm-3. For comparable uniformly doped Ga-polar SL samples, a mobility of 11 cm2/V s was measured. These results confirm the presence of abrupt Mg doping profiles in N-polar p-type GaN/AlxGa(1-x)N SL, allowing the demonstration of SLs with properties comparable to those of state-of-the-art Ga-polar modulation doped AlGaN/GaN SLs grown using molecular beam epitaxy. The lowest sheet resistance in the GaN/AlGaN material system of 5 kω/â-» is also reported. Test-structure transistors were also fabricated to investigate the applicability of these SL structures, with the planar device resulting in a current of 5 mA/mm and a FinFET structure resulting in a current of over 100 mA/mm.