Polarization fields in III-nitride nanowire devices

Control of the polarization fields is the most important parameter in designing III-nitride thin-film devices, and herein we show that the polarization fields may be equally, if not more, important in devising III-nitride nanowire devices. One common approach to produce III-nitride nanowires is via a vapor-liquid-solid approach that, in general, yields nanowires with the major (growth) axis in the < 11 (2) over bar0 > direction. The cross section of this wire is an isosceles triangle with two {1 (1) over bar 01} facets and one {0001} facet. In this work, we analyze the polarization fields that arise in two distinct sets of crystal planes that can manifest in this triangular nanowire geometry: (0001), (1 (1) over bar0 (1) over bar), ((1) over bar 10 (1) over bar) or (000 (1) over bar), (1 (1) over bar 01), ((1) over bar 101). Calculations show that the polarization field at the {0001} facet is much larger than at the two opposing {1 (1) over bar 01} facets, although the sign of the field at each facet has a complicated dependence on the orientation and structure of the nanowire. An undoped nanowire transistor was fabricated that displayed p-type operation based solely on polarization-induced hole carriers at the (000 (1) over bar) AlGaN/GaN interface, consistent with our field calculations.