Electrical properties of solution processed layers based on Ge-Si alloy nanoparticles
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Electrical properties of solution processed layers based on Ge-Si alloy nanoparticles Zeynep Meric1, Christian Mehringer2, Michael. P. M. Jank3, Wolfgang Peukert2, Lothar Frey1,3 1
Chair of Electron Devices, University of Erlangen-Nürnberg, Erlangen, 91058, Germany Institute of Particle Technology, University of Erlangen-Nürnberg, Erlangen, 91058, Germany 3 Fraunhofer Institute for Integrated Systems and Device Technology (IISB), Erlangen, 91058, Germany 2
ABSTRACT Ge-Si alloy nanoparticles (NPs) covering the full range of compositions were studied in regard to their suitability as semiconducting channel layer in thin-film transistors (TFTs). Special focus is given to the influence of annealing and encapsulation techniques on the contact and channel properties. Therefore, electrical characterization methods separating contact from channel characteristics are highlighted and applied. It is demonstrated that appropriate passivation of the nanoparticle surfaces can improve the Ion/Ioff ratios by modulation of the density of free charge carriers and also can suppress hysteresis effects. Ge-rich NP alloys can generally be passivated more effectively regardless if passivation is done with solution-processed poly(methyl methacrylate) (PMMA) or by aluminum oxide (Al2O3) from Atomic Layer Deposition (ALD). Sufficient annealing improves the contact formation between aluminum electrodes and Ge-Si particles by modification of charge injection. The presented analysis leads to a better understanding interface and surface effects in porous nanoparticle semiconductors for application in TFT devices. INTRODUCTION Nanoparticles are a prospective type of universal building blocks for functional films. They promise facile production of electronics through external materials synthesis, solutionbased, e.g. additive print processing employing flexible substrates, and low temperature curing schemes. In this work we focus on germanium (Ge) - silicon (Si) alloy NPs and the resulting nanolayers. As with all porous NP films, a central problem is the control of conductivity, both intrinsic and due to external fields, e.g. for use in TFT-like devices. Films deposited from solvents perform poorly in this regard and consequently require elaborated post-treatment [1]. In our previous studies on pure Si NPs [2] and pure Ge NPs [3] we focused on the surface preparation and its effect on conductivity. Employing pure Ge NPs, surface modification is highlighted to be used for both improvement of device characteristics and influencing the conduction type to allow both n-type and p-type behavior and even ambipolarity. This work bridges the gap between the studies by analyzing the influence of the alloy composition on the observed behaviors. We therefore refined the previously established approaches and applied them to the full range of GexSi1-x compositions including pure Ge as well as pure Si systems. EXPERIMENT The alloy NP production is explained in detail elsewhere [4]. All alloy NP batches were introduced into the glovebox without contact to air. T
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