Polarity analysis of GaN nanorods by photo‐assisted Kelvin probe force microscopy

Abstract

Polarity dependence (N‐polar (000‐1) and Ga‐polar (0001)) of surface photovoltage of epitaxially grown, vertically aligned GaN nanorods has been investigated by photo‐assisted Kelvin probe force microscopy (KPFM). Commercial GaN substrates with known polarities are taken as reference samples. The polarity of GaN substrates can be well distinguished by the change in surface photovoltage upon UV illumination in air ambient. These different behaviors of Ga‐ and N‐polar surfaces are attributed to the polarity‐related surface‐bound charges and photochemical reactivity. GaN nanorods were grown on patterned SiO2/sapphire templates by metal‐organic vapor phase epitaxy (MOVPE). In order to analyze the bottom surface of the grown GaN nanorods, a technique known from high power electronics and joining techniques is applied to remove the substrate. The top and bottom surfaces of the GaN nanorods are identified to be N‐polar and Ga‐polar according to the KPFM results, respectively. Our experiments demonstrate that KPFM is a simple and suitable method capable to identify the polarity of GaN nanorods. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN based nanorods for solid state lighting

“…Both KPFM and wet chemical etching results proved that the GaN nanorods grown in this work are almost completely N-polar. 60 The comparison results of GaN nano-/sub-lm rod growth on unstrained N-polar and Ga-polar quasi-substrates indicate that strain does not play a critical role for the development of GaN sub-lm rods. In general, the polarity determines the degree of vertical growth, finally leading to GaN nanorods.…”

“…Besides, depending on the growth methods and conditions, the properties of the GaN nanorods can be strongly varied. Although there are a few publications devoted to the characterization of N-polar nanorods, 41,60 systematic comparisons of the properties of GaN nanorods with N-and Ga-polarity is still missing.…”

Vertical current-flow enhancement via fabrication of GaN nanorod p–n junction diode on graphene

“…When the tip and the sample surfaces are charged, a potential (V cpd ) develops between them. The negative DC voltage (V DC ) required to nullify the so formed V cpd is the measure of work function difference in between the tip and the sample [29][30][31].…”

GaN nanowires on diamond

“…One possible method to address a high number of NWs separately is Kelvin Probe Force Microscopy (KPFM), where the contact potential difference (CPD) between a modified AFM tip and single NWs can be resolved [45]. Indeed, this technique has already been used by several groups to investigate the polarity of thin films and individual GaN NWs [46][47][48][49]. Most groups have measured KPFM in two steps, with and without UV illumination.…”