Regensburg 2007 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 45: ZnO II
HL 45.6: Vortrag
Donnerstag, 29. März 2007, 15:15–15:30, H17
Effects of annealing on the recombination dynamics of low-temperature grown ZnO nanorods — •B. Hilker1, C. Bekeny1, T. Voss1, J. Gutowski1, R. Hauschild2, H. Kalt2, B. Postels3, Andrey Bakin3, and A. Waag3 — 1IFP, Universität Bremen, 28334 Bremen — 2Universität Karlsruhe, 76128 Karlsruhe — 3IHT, TU Braunschweig, 38023 Braunschweig
We present systematic temperature and excitation density dependent time-resolved photoluminescence (TRPL) measurements of as-grown and annealed ZnO nanorods fabricated by an aqueous chemical growth (ACG) technique at ~90°C. The as-grown nanorods show strong near-band-edge and rather weak deep-level emission indicating their already good optical quality. At 4K, we find a broad emission line at 3.36eV (line width 30meV) which we attribute to recombination from a donor band formed through the high donor concentration. After annealing in oxygen and nitrogen atmospheres at 600-800°C well-resolved and sharper excitonic transitions are observed. To understand the recombination dynamics in the nanorods we carried out TRPL measurements using a frequency-doubled femtosecond laser and a streak camera. The as-grown sample shows a very fast monoexponential decay time of ~10ps independent of temperature and excitation density. In contrast, the annealed samples exhibit a biexponential decay. Each a fast τ1 and a slow τ2 time constant have been determined for all annealed samples both of them significantly varying depending on the annealing atmosphere and temperature. This will be discussed on the basis of a phenomenological rate-equation model.