Optical characterization of GaN doping superlattices as grown, hydrogen implanted and annealed.

Herbert Willi Kunert 1D J. Brink 1Michael Hayes 1J. Malherbe 1L. Prinsloo 2Józef Barnaś 3

1. University of Pretoria, Department of Physics, University str., Pretoria 0084, South Africa
2. University of Pretoria, Department of Chemistry, Pretoria 0001, South Africa
3. Adam Mickiewicz University, Department of Physics, Umultowska 85, Poznań 61-614, Poland


GaN doping superlattices (DSL's) were grown epitaxially (MBE) with eight periods of n-GaN/p-GaN (50nm/50nm) doped: 1x1018cm-3(n-Si) and 1x1018cm-3(p-Mg) with a thin AIN nucleation layer (20nm) on a 2-inch single-side-polished sapphire (0001) wafer. Low temperature photoluminescence and Raman spectroscopy (PL), (RS)-respectively were used to characterize the as grown and hydrogen implanted (dose=1012-1017cm-2, Energy 1MeV), samples. From the as grown sample the PL yields the well known DAP's band. In addition, in the region 2.1-2.8 eV (where normally the YL band is observed in bulk Mg-doped GaN) we monitor several mini, well-resolved separate bands these do not resemble theYL band. Temperature and laser power dependence do not affect the energy position of these peaks. Implantation decreases the intensities of most bands but does not induce new optically active transitions. Annealing at 900C reveals a broad solid unstructured YL band centred at 2.3 eV.
In bulk GaN there are six allowed Raman active modes. In the GaN DSL's reference sample we observe vibrational modes at 428 cm-1 (sapphire substrate mode), 572cm-1-E2(high) - like which normally is centred at 572cm-1, and a mode at 738cm-1 which originate from the A1(LO)-735cm-1 bulk GaN. Implantation at low doses shifts the modes slightly while higher doses influence mostly the second order vibrational modes. We observe two implantation enhanced modes at 1400 and 1440cm-1. The half-width of the strongest mode at 572cm-1 increases with implantation dose indicating structural damage.
Applying the Ploog-Dohler approach to the GaN DSL's, the quantum mechanical calculations on the lifetime of carriers yields a large value (compared with GaAs DSL's). Mechanisms for the origin of the annealing-induced YL band and the observation of eight mini bands are discussed. Raman selection rules for the second order modes in the GaN DSL's are discussed.


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Presentation: poster at E-MRS Fall Meeting 2003, Symposium A, by Herbert Willi Kunert
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-07 13:27
Revised:   2009-06-08 12:55