Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 25: Symposium: II-VI Halbleiter

HL 25.1: Fachvortrag

Mittwoch, 13. März 2002, 14:30–15:00, H15

Defects and doping in ZnO — •B. K. Meyer, A. Zeuner, H. Alves, and D. M. Hofmann — 1.Physics Institute, Justus Liebig University Giessen, Heinrich-Buff-Ring 16, 35392 Giessen, Germany

ZnO and its ternary alloys ZnMgO and ZnCdO have the potential to compete with the III-V nitrides for opto-electronic devices operating in the blue and ultraviolet regions. Like GaN ZnO is a direct band gap semiconductor with a room temperature energy gap at 3.3 eV (375 nm), it has comparable piezoelectric constants as GaN, and also crystallizes in the wurtzite-type structure. Excitonic lasing at low thresholds at room temperature has been reported recently. As-grown ZnO naturally has n-type conductivity with background concentrations between 1016 and 1017 cm-3. A clear atomistic identification of the residual shallow donors was not possible up to now. In a recent EPR and ENDOR investigation on bulk ZnO we could show that unintentionally present Hydrogen is a shallow donor with an activation energy of 35 meV. We will report on annealing experiments which give evidence that H-donors can be removed from the material.
We present recent result on the growth of ZnO epitaxial films on GaN templates by chemical vapor deposition. A comparison is made between the defects present in the undoped films and in the bulk crystals.
P-type doping of ZnO remained a challenge through all the years and judging from the limited number of papers on p-type conduction it is very difficult to obtain. Also there is a limited choice of suitable dopant impurities. Out of the group V elements Nitrogen was considered to be the best candidate having in mind the success in achieving p-type ZnSe:N. N doping was realized through the thermal decomposition of ammonia. The observation of N-related local vibrational modes by Raman spectroscopy confirms that N is incorporated at O-sites. However, a strong correlation to unintentional present Hydrogen is found using SIMS suggesting a passivation of the N-acceptors. The optical signature of the N-acceptor is seen in the donor-acceptor pair recombination with an acceptor binding energy of appr. 150 meV. Similarities to ZnSe:N are evident.