Microreactor-Assisted Solution Deposition for Compound Semiconductor Thin Films

Abstract

State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures and lower capital costs. Among many solution-based deposition processes, chemical bath deposition is an attractive technique for depositing semiconductor films, owing to its low temperature, low cost and large area deposition capability. Chemical bath deposition processes are mainly performed using batch reactors, where all reactants are fed into the reactor simultaneously and products are removed after the processing is finished. Consequently, reaction selectivity is difficult, which can lead to unwanted secondary reactions. Microreactor-assisted solution deposition processes can overcome this limitation by producing short-life molecular intermediates used for heterogeneous thin film synthesis and quenching the reaction prior to homogeneous reactions. In this paper, we present progress in the synthesis and deposition of semiconductor thin films with a focus on CdS using microreactor-assisted solution deposition and provide an overview of its prospect for scale-up. OPEN ACCESSProcesses 2014, 2 442 IntroductionCompound semiconductors play an important role for generating, emitting and manipulating energy. State-of-the-art techniques for the fabrication of compound semiconductors are mostly vacuum-based physical vapor or chemical vapor deposition (CVD) processes. These vacuum-based techniques typically operate at high temperatures and normally require higher capital costs. Solution-based techniques offer opportunities to fabricate compound semiconductors at lower temperatures and lower capital costs. Other additional advantages of the solution-phase routes are the availability of large resources of synthetic strategies and the compatibility with soft organic materials. A variety of solution-based techniques, including electrodeposition, successive ionic-layer adsorption and reaction, spray pyrolysis and chemical bath deposition (CBD) have been developed for the fabrication of compound semiconductors [1-3]. Among these, CBD is an attractive technique owing to its low temperature, low cost and large area deposition capability [4,5]. Many semiconductor thin films have been successfully deposited using this technique, and it has already been proven to be a very useful method for fabricating large area devices, such as high efficiency CuInSe 2 and CdTe solar cells. CBD processes are mainly performed using batch reactors, where all reactants are fed into the reactor and products are removed after the processing is finished. These batch processes can suffer from slow heat and mass transfer, which can result in large temperature, concentration and solution pH gradients. Microreactor-assisted nanomaterial deposition (MAND) processes can overcome some of the li...

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