Persistent photoconductivity studies of c-axis GaN nanowires grown by MBE

Published

September 16, 2007

Author(s)

Norman Sanford, Paul T. Blanchard, Kristine A. Bertness, Alexana Roshko, Beau Burton, Lorelle Mansfield, John B. Schlager, Steven George, Aric Sanders

Abstract

Photoconductivity (PC) and persistent photoconductivity (PPC) were measured on c-axis GaN nanowires (NWs) grown by catalyst-free nitrogen plasma assisted MBE on Si(111) substrates. Unintentionally doped n-type NWs from two separate growth batches were examined. NWs were stripped from growth substrates and fabricated into test structures on fused quartz plates. Test structures were composed of: (i) 2-terminal electrically-contacted wires that were laying directly on the quartz substrates; (ii) bridge structures with the electrical contacts used to suspend the wires above the quartz plates by roughly 300 nm. In both cases the separation between the electrical contacts was approximately 3 m. NWs from the first batch ranged from 50 to 100 nm in diameter with larger diameter structures typically consisting of grown-together clusters composed of two or more wires. The second batch of wires also showed larger-diameter grown-together assemblies but yielded many larger-diameter structures composed of single well-formed wires. Samples were tested under 360 nm flood illumination at 3 mW/cm2 with biases in the 1-4 V range. PPC with durations ranging up to several hours were observed for the thicker grown-together wire clusters. By contrast both thin and thick single NWs generally showed PPC that would decay in a few minutes or less. The multi-wire clusters also displayed long PPC when illuminated sub-gap . Atomic layer deposition (ALD) of conformal alumina films roughly 10 nm thick on the NWs would increase the PPC by an order of magnitude or more in all cases. On the other hand, conformal ALD deposition of TaN films was comparatively benign. The observations are interpreted as resulting from traps and midgap states occurring on the NW surfaces and at defects and grain boundaries in the multi-wire assemblies. These effects are further complicated by ALD coating of the surfaces of these structures.

Conference Dates

September 16-21, 2007

Conference Location

Las Vegas, NV, USA

Conference Title

7th International Conference on Nitride Semiconductors

Pub Type

Conferences

Keywords

gallium nitride, GaN, nanorods, nanotechnology, nanowires, wide bandgap semiconductors

Citation

Sanford, N. , Blanchard, P. , Bertness, K. , Roshko, A. , Burton, B. , Mansfield, L. , Schlager, J. , George, S. and Sanders, A. (2007), Persistent photoconductivity studies of c-axis GaN nanowires grown by MBE, 7th International Conference on Nitride Semiconductors, Las Vegas, NV, USA (Accessed October 28, 2025)