Electronic properties of the ZnO:Al/n-Si (100), (110) and (111) interfaces
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Electronic properties of the ZnO:Al/n-Si (100), (110) and (111) interfaces Per Lindberg1, Vincent Quemener1, Kristin Bergum2, Jiantuo Gan1, Bengt G. Svensson1 and Edouard V. Monakhov1 1 Department of Physics/Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1048 Blindern, N-0316 Oslo, Norway. 2 Department of Chemistry/Centre for Materials Science and Nanotechnology, University of Oslo, P.O. Box 1126 Blindern, N-0318 Oslo, Norway. ABSTRACT Aluminum doped ZnO (AZO) has been deposited on (100), (110) and (111) oriented n-type Si and on fused silica by atomic layer deposition (ALD). The films have been post deposition annealed in the temperature range 200-500 οC. The AZO films have been characterized by X-ray diffraction (XRD), Hall and transmittance measurements. Circular diodes have been fabricated from the AZO/Si structures and characterized by current-voltage (IV) and deep level transient spectroscopy (DLTS). The AZO films form Schottky junctions with the Si substrates for all the crystallographic orientations. It is established that after post deposition annealing the structure AZO/n-Si (110) is distinguished as the system with largest rectification. INTRODUCTION Aluminum doped ZnO (AZO) films on Si are of great relevance for several applications in electronics and photovoltaics. The electrical properties of the heterostructures AZO/Si are dominated by interface properties [1]. It has previously been reported that AZO deposited on Si by 'soft' deposition techniques, such as atomic layer deposition (ALD), creates heterojunctions with less interfacial defects hence giving rise to larger rectification than if deposited with more ‘violent’ techniques, such as magnetron sputtering [2]. The electrical, optical and structural characteristics of the ZnO/Si interface has been reported in many publications during the last decades [1 and 3 and references therein]. However, there are only a few reports determining the energy levels and concentration of the interface defects [2, 4, 5]. To the best of our knowledge, there has so far been no study comparing the interface properties of heterojunctions of AZO on Si with different crystallographic orientations. In the present work we have compared the electrical, and to some extent structural, characteristics of the junction between AZO and (100), (110) and (111) Si using XRD, IV and DLTS. EXPERIMENTAL DETAILS The AZO films were deposited in a Beneq TFS 200 ALD reactor. The N2 carrier gas was supplied by a Sirocco N2 generator (N2>99.9999 %). The deposition temperature was 200 oC for all films. Evaporated at room temperature, trimethylaluminum (TMA), diethylzinc (DEZ) and water were used as precursors. The pulsing times for the precursors were well within the ALDgrowth regime. After each pulse of precursor, N2 was purged for 1 s. DEZ was pulsed for 0.3 s followed by a water pulse for 0.15 s. The cycle was repeated 11 times before ethanol was pulsed
for 0.25 s, followed by TMA pulsed for 0.15 s and at last 0.75 s water-pulse ended the cycle. This procedu
