Spatially Resolved Characterization of Plastic Deformation Induced by Focused-Ion Beam Processing in Structured InGaN/GaN Layers
- ORNL
- University of Bremen, Bremen, Germany
- Argonne National Laboratory (ANL)
In this study the results of polychromatic X-ray microbeam analysis (PXM) of the structural changes caused by FIB in nitride heterostructures are presented and discussed in connection with micro-photoluminescence ( -PL) and transmission electron microscopy (TEM) data. Using an FEI Nova 200 NanoLab FIB system reference structures have been prepared in samples consisting of InGaN/GaN multi quantum wells grown by metal-organic vapor phase epitaxy on GaN on sapphire templates. Each structure consists of several trenches typically 2 m wide and 20 m long with varying distances between the trenches. Trenches were etched down to the sapphire substrate using 30 keV Ga-ions and different ion-beam currents varying from 300 pA to 7 nA. Results from samples with and without a 100 nm SiO2 protection layer are compared. The -PL analysis reveals a fatal surface damage on a large scale when working on unprotected samples. For protected samples a decrease in the PL intensity is found only in the immediate vicinity of the trenches. For PXM measurements the microbeam was scanned parallel to the trenches structured in the InGaN/GaN layer with FIB. Laue patterns were recorded at 50 different sample positions. Due to the small size of the microbeam (0.5 m) it was possible to obtain spatially resolved data from different locations around the trenches. Because the high-energy (8-25 keV) x-ray beam penetrates through the InGaN/GaN and probes the sapphire substrate as well, they both contribute to the observed Laue patterns. The sapphire reflections do not change position with sample translation. They were used as a reference to determine the change in orientation of the InGaN/GaN layer relative to the substrate. The PXM results show that FIB etching distorts the lattice in the InGaN/GaN layer not only in the immediate trench region but in the surrounding area as well. Lattice planes become curved with curvature radius dependent on the distance from the trench, FIB current and the capping layer. The observed lattice distortion is caused by a severe microstructural change which was analyzed using TEM. The TEM analyses in the vicinity of the trenches shows a high density of dislocations and an amophidized layer on top, which could be due to direct surface damage by the FIB beam or redeposition. The research was supported in part by the U. S. Department of Energy, Division of Materials Sciences and Engineering through a contract with the Oak Ridge National Laboratory. Oak Ridge National Laboratory (ORNL) is operated by UT-Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725. Data collection with PXM has been carried out on beamline ID-34-E at the Advanced Photon Source, Argonne IL, and supported by the U.S. DOE under Award No. DEFG02-91ER45439. This work was further supported by the Deutsche Forschungsgemeinschaft under Contracts No. HE 2827/5-1 and HO 1388/25-2.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 931779
- Resource Relation:
- Conference: 2007 Materials Research Society Spring Meeting, San Francisco, CA, USA, 20070409, 20070413
- Country of Publication:
- United States
- Language:
- English
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