Study of the effect of the deposition RF power on the characteristics of microcrystalline Silicon-Germanium thin films p
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.645
Study of the effect of the deposition RF power on the characteristics of microcrystalline SiliconGermanium thin films produced by PECVD Arturo Torres1, Mario Moreno1, Pedro Rosales1, Miguel Domínguez2, Alfonso Torres1, Adrian Itzmoyotl1, Roberto Ambrosio2, Javier de la Hidalga1 1
2
National Institute of Astrophysics Optics and Electronics, INAOE, Puebla, México.
Meritorious Autonomous University of Puebla, BUAP, Puebla, México.
ABSTRACT
Hydrogenated microcrystalline Silicon-Germanium (μc-SiGe:H) thin films were deposited using the Plasma Enhanced Chemical Vapor Deposition (PECVD) technique from a gas mixture of SiH4, GeH4, H2 and Ar at a substrate temperature of 200 ° C. The films were deposited at a pressure of 1.5 Torr, while the RF power was varied in the range of 20 W to 35 W. Structural, optical and electrical characterization was performed in the films, Fourier Transform Infrared Spectroscopy (FTIR) was performed in order to analyze the hydrogen bonding of silicon and germanium, while Raman spectroscopy was used in order to analyze the crystallinity of the films. Through the optical and electrical characterization of the films, parameters such as the optical band gap (Eg) and the activation energy (EA) were obtained, respectively. The conductivity of the films changed up two to orders of magnitude from dark conditions to illumination AM 1.5. Finally, the correlation between deposition RF power and the film properties is presented.
INTRODUCTION Hydrogenated microcrystalline silicon (μc-Si:H) has established as a mature technology in thin film-based devices, due to its low temperature of deposition (< 200 ° C) in the standard Plasma Enhanced Chemical Vapor Deposition (PECVD) technique, using a variety of substrates (glasses, metal foils, flexible plastic substrates, etc.). However, the disadvantages of μc-Si:H are its relatively weak absorption at large wavelengths (infrared radiation) and low
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hole mobility compared with the mobility of electrons. As a consequence, have emerged silicon and germanium alloys such as hydrogenated microcrystalline silicon-germanium (μc-SiGe:H) which is obtained also by PECVD at low temperatures. The advantages of μc-SiGe:H is that it has an absorption coefficient more than one order of magnitude larger than that of μc-Si:H in the infrared region (IR) of the spectrum, which is suitable for tandem thin film solar cells [1]. Another advantage of the Si-Ge alloys is the comparable mobility of their charge carriers (holes and electrons), moreover ambipolarity has been observed in thin film transistors (TFTs) using Si-Ge alloys as an active layer [2]. Many works have been developed to obtain films of µc-SiGe:H deposited by PECVD with a narrow band gap and high photosensit
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