K. MUTAMBA, M. SAGLAM, C. SYDLO, A. MEGEJ, H. L. HARTNAGEL, I. DAUMILLER
Varactor Diodes on the Basis of Al_0.4Ga_0.6N/GaN Heterostructures

Abstract.
This paper reports on the electrical characteristics of MOCVD-grown Al_xGa_1/xN /GaN (x = 0.4) heterostructure barrier varactors. The influence of strong piezoelectric and spontaneous polarisation effects is highlighted by the asymmetric behaviour of the capacitance-voltage characteristics of the fabricated devices. The obtained capacitance modulation values of 1.4 and 1.1 for negative and positive bias, respectively, show that an appropriate bandgap engineering is needed in order to take advantage of the offered higher barrier heights of nitride-based heterostructures. A theoretical analysis including polarisation charges at layer interfaces and the resulting effects on the device energy band-diagram supports the obtained results.