Dual-Chamber Plasma Co-Deposition of Nanoparticles in Amorphous Silicon Thin Films
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0910-A04-02
Dual-Chamber Plasma Co-Deposition of Nanoparticles in Amorphous Silicon Thin Films C. Anderson1, C. Blackwell2, J. Deneen3, C. B. Carter3, J. Kakalios2, and U. Kortshagen1 1 Mechanical Engineering, University of Minnesota, Minneapolis, MN, 55455 2 Physics and Astronomy, University of Minnesota, Minneapolis, MN, 55455 3 Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, 55455 ABSTRACT The production of hydrogenated amorphous silicon films containing silicon nanocrystalline inclusions (a/nc-Si:H) is demonstrated using a new deposition process. Crystalline Si nanoparticles around 5 nm in diameter are generated in a flow-through plasma reactor, and are introduced into a downstream capacitively-coupled plasma enhanced chemical vapor deposition reactor where the particles are “co-deposited” with the amorphous phase of the film. Transmission electron microscopy confirms the presence of crystalline inclusions in these films, as well as providing confirmation that the crystalline particles are indeed produced in the flow-through reactor and not in the capacitive plasma. Electrical measurements indicate an improvement in the dark conductivity of the intrinsic a/nc-Si:H films as the particle concentration is increased, suggesting that the particles have a doping effect on the films charge transport properties. INTRODUCTION Hydrogenated amorphous silicon thin films with nanocrystalline silicon inclusions (a/ncSi:H) have attracted considerable recent attention owing to reports of improved charge transport properties. An increased resistance to light induced defect formation (the Staebler-Wronski effect (SWE)) is found in these mixed phase films [1,2,3]. The role of the nanometer sized crystallites on the electronic transport and defect structure of a-Si:H remains poorly understood. These films are typically synthesized in a single-chamber capacitively-coupled plasma enhanced chemical vapor deposition (PECVD) system, using high gas pressures (1-2 Torr) and heavily hydrogen-diluted silane precursors [3,4]. This single-chamber process poses limitations for the production of a/nc-Si:H, since the properties of the crystalline particles produced in the gas phase are not easily controlled. Also of concern is the fact that these chamber conditions are not conducive to growing high quality amorphous material. In order to better understand the properties of mixed-phase materials, it would be advantageous to have control over the structure of the a/nc-Si:H film in terms of crystallite size and number density. In this paper, we present a new process for the production of a/nc-Si:H in which the crystalline and amorphous phases of the films are generated in separate plasma reactors. Crystalline nanoparticles 3-5 nm in diameter are produced in an upstream flow-through reactor and are then introduced into an amorphous silicon matrix. We report for the first time the structure, infrared absorption, and electrical properties of a/nc-Si:H films produced by this new method.
Figure 1: Schematic of th
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