Wafer Bonded Ge-Si Heterostructure for Avalanche Photodiode Application
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Wafer Bonded Ge-Si Heterostructure for Avalanche Photodiode Application
Ki Yeol Byun1, John Hayes1, Farzan Gity1, Brian Corbett1, and Cindy Colinge1 1 Tyndall National Institute, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland.
ABSTRACT In this study, we investigate directly bonded germanium-silicon interfaces to facilitate the development of high quality germanium silicon integration for Avalanche photodiode application. Angle resolved x-ray photoelectron spectroscopy data is presented which provides the chemical composition of the germanium surfaces as a function of the surface passivation. The hetero-structure is characterized by measuring forward and reverse current and comparing the measured results to TCAD simulation. The physical structure of hetero-junction is supported by high resolution transmission electron microscopy. INTRODUCTION Avalanche photodiodes (APD) have been used widely in optical communication systems to detect and amplify weak optical signals using the internal gain provided by impact ionization. These components have been available for several years from the III/V semiconductor technology using InP and GaAs wafers. Nevertheless, the integration of these devices on large wafers within the mainstream silicon technology requires either high-cost hybrid integration approach or back-end technology [1]. The integration of germanium (Ge) on silicon (Si) increases absorption, leading to possible photodetection at telecommunication wavelengths (from 1.31um to 1.55um). Recently, it has been demonstrated that pure Ge is a promising candidate as a broadband photodetector [2, 3]. Furthermore, Ge based optical communication circuits can be monolithically integrated with Si CMOS technology. However, conventional epitaxial Ge growth requires careful processing and device design to minimize the impact or increase of the dislocations. It is well known that defects and dislocations are generation centers that contribute to the leakage current in minority carrier devices [4]. In this work, we propose an alternative method for producing the Ge-Si APD by wafer bonding, which has, potentially, less defective interfaces and employs a low thermal budget. Moreover, the bonded Ge wafer can be thinned by mechanical thinning or splitting after wafer bonding [5, 6]. The transitions of chemical component on the Ge surface are determined using angle resolved x-ray photoelectron spectroscopy (AR-XPS) as a function of chemical passivation to understand the species present at the bond interface. Based on the surface chemistry of the Ge surface, we investigate the electrical properties of the bonded Ge-Si hetero-interface. Characterization of the Ge-Si hetero-junction is achieved by measuring the forward and reverse currents and comparing the results with TCAD simulations. Further, the hetero-interface is characterized by high resolution transmission electron microscope (HR-TEM). Our results show
that successful Ge-Si hetero-structure using hydrophobic low temperature wafer bonding can be realized for av
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