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Free and bound excitons in thin wurtzite GaN layers on sapphire

Freie und gebundene Exzitonen dünner alpha-GaN Schichten auf Saphirsubstrat
: Merz, C.; Kunzer, M.; Kaufmann, U.; Akasaki, I.; Amano, H.


Semiconductor Science and Technology 11 (1996), S.712-716
ISSN: 0268-1242
ISSN: 1361-6641
Fraunhofer IAF ()
exciton; Exziton; GaN; Mg; photoluminescence; Photolumineszenz; Si; thermal induced strain; thermisch induzierte Verspannung

Free and bound excitons have been studied by photoluminescence in thin (1-10 microm) wurtzite-undoped GaN, n-type GaN:Si as well as p-type GaN:Mg and GaN:Zn layers grown by metal-organic chemical vapour phase deposition (MOCVD). An accurate value for the free A exciton binding energy and an estimate for the isotropically averaged hole mass of the uppermost Gamma(ind 9) valence band are deduced from the data on undoped samples. The acceptor-doped samples reveal recombination lines which are attributed to excitons bound to Mg(exp 0) and Zn(exp 0) respectively. These lines are spectrally clearly separated and the exciton localization energies are in line with Haynes' rule. Whenever a comparison is possible, it is found that the exciton lines in these thin MOCVD layers are ultraviolet-shifted by 20 to 25 meV as compared to quasi-bulk (>= 100 microm) samples. This effect is interpreted in terms of the compressive hydrostatic stress component which thin GaN layers experience when grown on sa pphire with an AIN buffer layer.