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HL: Halbleiterphysik

HL 26: II-VI semiconductors II

HL 26.6: Vortrag

Dienstag, 28. März 2006, 16:30–16:45, POT 51

Photoluminescence investigations on a native donor in ZnO — •Joachim Sann, Niklas Volbers, Stefan Lautenschläger, and Bruno K. Meyer — I. Physikalisches Institut, Justus-Liebig-Universität, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany

The shallow donor impurities in ZnO with binding energies between 46 and 56 meV have been studied in great detail in the recent years. They give rise to neutral donor bound exciton recombinations with the A- and B-valence bands, show rotator states and two-electron-satellite transitions. These properties allowed to establish the excited state splittings of the donors as well as confirming Hayne’s rule in ZnO. So far they all seem to be of extrinsic origin, hydrogen, aluminum, gallium and indium in order of increasing binding energy. For many years it was common sense that intrinsic defects would dominate the n-type conductivity of ZnO. Interstitial zinc as well as oxygen vacancies should be double donors, and in order to contribute to the n-type-conduction they should have shallow levels, and low formation energies to be abundant. Undoped Zn-rich epitaxial films grown by CVD on GaN/Sapphire-templates as well as on ZnO templates show a dominant I_3a recombination at 3.367 eV in low temperature PL which according to Haynes rule is consistent with a shallow donor level at 37 meV. Moreover, they have free n-type carrier densities of 8x10¹⁸ cm⁻³ and as revealed by SIMS the common donor impurities (Al, Ga, In) cannot account for the high carrier densities. By changing the Zn/O ratio towards oxygen rich conditions the I_3a recombination is suppressed, a similar effect is found when annealing in oxygen atmosphere.