Regensburg 2010 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 57: Focussed Session: ZnO-based Semiconductors

HL 57.13: Talk

Thursday, March 25, 2010, 17:45–18:00, H17

Majority and minority carrier traps in a n - type ZnO thin film — •Matthias Schmidt, Martin Ellguth, Holger v. Wenckstern, Rainer Pickenhain, and Marius Grundmann — Universität Leipzig, Institut für Experimentelle Physik II, Leipzig, Germany

The majority of the published deep level transient spectroscopy (DLTS) data on defects in ZnO stems from energy levels in the upper third of the ZnO band gap. This is due to the p doping difficulty and the wide band gap. Only few reports on DLTS studies using pn junctions for the investigation of hole traps in the vicinity of the valence band exist.

In this work we investigated defects present in a ZnO thin film grown by pulsed laser deposition on a two side polished a-plane sapphire substrate. Space charge regions (SCR) were provided by Pd Schottky contacts. We employed standard DLTS for the detection of majority carrier traps, e.g. E3. Using the double DLTS technique, we observed the Poole Frenkel effect for the E3 deep level. Hole traps were studied by minority carrier spectroscopy, a DLTS technique, where instead of the voltage pulse a UV LED pulse illuminates the sample from the back such that electron hole pairs are created. Due to the electric field at the Schottky barrier, the electrons drift towards the bulk and the holes into the SCR. In doing so, hole traps are filled during the pulse and hole emission is observed by DLTS. These experiments revealed the existence of a deep level approx. 430 meV above the valence band.