Abstract
The electrical behaviour of Schottky barrier diodes realized on vertically standing individual GaN nanorods and array of nanorods is investigated. The Schottky diodes on individual nanorod show highest barrier height in comparison with large area diodes on nanorods array and epitaxial film which is in contrast with previously published work. The discrepancy between the electrical behaviour of nanoscale Schottky diodes and large area diodes is explained using cathodoluminescence measurements, surface potential analysis using Kelvin probe force microscopy and 1ow frequency noise measurements. The noise measurements on large area diodes on nanorods array and epitaxial film suggest the presence of barrier inhomogeneities at the metal/semiconductor interface which deviate the noise spectra from Lorentzian to 1/f type. These barrier inhomogeneities in large area diodes resulted in reduced barrier height whereas due to the limited role of barrier inhomogeneities in individual nanorod based Schottky diode, a higher barrier height is obtained.
Highlights
GaN nanostructures are intensively investigated due to advantages like capabilities of incorporation of both nand p-type dopants[1,2], strain relaxation when grown on lattice mismatched substrates[3,4], dislocation free structures[5] and enhanced light absorption[6]
To realize a nanoscale device based on GaN nanorods (NRs), a thorough understanding of the current transport across interface is required as models which are used for explaining electrical transport in epitaxial films are not fully applicable to nano-devices because of small dimensions[19,20]
Almost similar diameters of NPs and NRs confirmed that NPs acted as masks during inductively coupled plasma-reactive ion etching (ICP-RIE) of SiO2 and GaN
Summary
GaN nanostructures are intensively investigated due to advantages like capabilities of incorporation of both nand p-type dopants[1,2], strain relaxation when grown on lattice mismatched substrates[3,4], dislocation free structures[5] and enhanced light absorption[6]. Contrast to larger area diodes, effect of barrier inhomogeneities and interface states on electrical behaviour on nanoscale diodes is expected to be different due to reduced dimensions. For employing semiconductor nanostructures into promising device technology, the correlation between surface properties, barrier inhomogeneities, interface states and electrical transport properties needs to be understood i.e. how the surface of individual nanostructure is contributing to the device characteristics. Present work compares the electrical behaviour of nanoscale Schottky diodes formed on individual GaN nanorod with large area diodes formed on array of GaN NRs and GaN epitaxial film. Comprehensive characterizations using micro-Raman spectroscopic, micro-photoluminescence (μ-PL), cathodoluminescence (CL) measurements and Kelvin probe force microscopy (KPFM) are performed to examine and compare the optical and surface potential properties of a single GaN nanorod as well as NRs array with respect to parent epitaxial film. 1/f noise measurements are performed on diodes fabricated on epitaxial film as well as on array of NRs
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