Development of large area dislocation defect reduced III-nitride layers on silicon (111) substrate.

摘要

An alternative method for the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been developed that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. The implantation induced crystallographic disorder partially isolates the III-Nitride layer(s) and the Si substrate and helps reduce the strain in the thin film. Nitrogen ion implantation energies of 60-75 KeV and ion doses in the range of 1x10 15 cm-2-2x1016 cm-2 were applied to 15-165 nm thick AlN buffer layers grown on Si (111) substrate.; Raman spectroscopy shows a substantial decrease in in-plane strain in GaN films grown on nitrogen implanted substrates translating into ∼80% stress reduction with its manifestation as the substantial decrease in crack density for a 2 mum thick GaN film as measured under optical microscope. GaN films grown on implanted AlN/Si substrate have better optical properties with lower FWHMs of band edge (at 10K) photoluminescence (PL) and the highest PL band edge to blue luminescence defect band ratio for the optimized AlN buffer thickness as compared to the unimplanted AlN/Si substrate. The optical quality and strain reduction in overgrown GaN films show a strong dependence on the implantation conditions and the thickness of buffer layer.; Results of etch pit density and XRD measurements show significant reduction in dislocations in III-Nitride layers for optimized experimental conditions. The formation of a polycrystalline defective layer at or slightly below the AlN/Si interface by N+ ion implantation provides substrate conditions that result in heteroepitaxial growth of GaN films with much improved surface morphology as well as crystal quality compared to the film grown directly on AlN/Si. A reduction of edge dislocations in GaN layer on Si substrate by almost an order of magnitude from 8.2x108/cm2 to 8.0x107/cm2 and reduction in screw dislocations by a factor of 9 was achieved as measured by TEM. A possible mechanism of strain and dislocation defect reduction has been put forward based on detailed HRTEM and HRXRD studies.