A DLTS study of a ZnO microwire, a thin film and bulk material
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A DLTS study of a ZnO microwire, a thin film and bulk material Florian Schmidt1, Peter Schlupp1, Stefan Müller1, Christof Peter Dietrich1, Holger von Wenckstern1, Marius Grundmann1, Robert Heinhold2, Hyung-Suk Kim2, and Martin Ward Allen2 1
Universität Leipzig, Institut für Experimentelle Physik II, Linnéstraße 5, 04103 Leipzig, Germany 2
The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury, Christchurch, New Zealand ABSTRACT We have investigated the electrical properties of a ZnO microwire grown by carbo-thermal evaporation, a ZnO thin film grown by pulsed-laser deposition on an a-plane sapphire, and a hydrothermally grown Zn-face ZnO single crystal (Tokyo Denpa Co. Ltd.). The samples were investigated by means of current-voltage measurements, capacitance-voltage measurements, and deep-level transient spectroscopy. The defects T2 [1,2] and E3 [1,3,4] were identified in all three sample types. Additionally, in the single crystal and thin film samples E64 [5] and E4 [1] were detected. These findings support the common opinion that T2 is an intrinsic defect since it is found in all the samples investigated and thus its occurrence is not related to any growth technique. INTRODUCTION ZnO ist the wide band-gap semiconducting oxide that was most intensively studied in the last decade. Nevertheless, the identification of other than effective mass defects is not accomplished yet despite enormous recent efforts. These include besides first-principles investigations, magnetic resonance studies also investigations by space-charge spectroscopic methods, especially deep-level transient spectroscopy (DLTS). Here, the defect parameters thermal activation energy and capture cross-section being a defect’s fingerprint are accessible. However, DLTS is “chemically blind” and hence an attribution of an electronic state to a certain impurity is indirectly possible, only. In this letter we investigate the relative concentration of the deep level defects T2 and E3 in ZnO samples that were realized by three different growth methods in order to come closer to their microscopic origin. EXPERIMENT Contact Properties Room temperature current-voltage (IV) measurements were applied using an Agilent 4156C precision semiconductor parameter analyzer and are shown in Fig. 1 (a) for all three ZnO structures.
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Figure 1. (a) Room temperature current-voltage characteristic of the microwire, thin film and single crystal, respectively. (b) Frequency-and (c) voltage dependence of the capacitance of all samples investigated.
The series resistance Rs, the shunt resistance Rp, and the rectification ratio RR defined by I(+1 V)/I(-1 V) were determined and are summarized in Tab. 1. Table 1. Series resistance Rs, shunt resistance Rp and rectification ratio RR obtained from room-temperature IV characteristics of ZnO Schottky diodes.
Sample Microwire thin film single crystal
Rs (Ω) 80k 61 115
Rp (Ω) 40M 6M 9G
RR 3×102 2×105 7 6 ×10
Frequency-dependent capacitance measurements reveal the influence of the series res
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