Electrical and Structural Characterization of the Interface of Wafer Bonded InP/Si
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Electrical and structural characterization of the interface of wafer bonded InP/Si A. Fontcuberta i Morral1, J. M. Zahler1, Harry A. Atwater1, M. M. Frank2, Y. J. Chabal2, P. Ahrenkiel3, M. Wanlass3 1 Thomas J. Watson Laboratory of Applied Physics, California Institute of Technology, Pasadena, CA 91125, U.S.A. 2 Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, NJ 08854, U.S.A. 3 National Renewable Energy Laboratory, Golden, CO 80401-3393, U.S.A. Abstract A study of the interfacial properties of wafer bonded InP/Si is presented. The electrical properties are measured by bonding InP to Si with different doping concentrations and by measuring the current voltage characteristics of the bonded pairs. Two different kinds of structures are studied: 1) n+InP doped to 3x1018 cm-3 bonded with n+Si doped to 1x1019 cm3 , and 2) n+InP doped to 3x1018 cm-3 bonded with p-Si doped to 6x1014 cm-3. After a 350oC anneal, structure 1 shows low resistive ohmic behavior while structure 2 is rectifying due to its higher sensitivity to interfacial chemistry. Indeed, both the reverse and forward current are reduced by annealing in structure 2, suggesting the formation of an interfacial barrier during annealing. This hypothesis is supported by High Resolution Transmission Electron Microscopy combined with Fourier Transform Infrared Spectroscopy, which indicate the formation of an amorphous interfacial oxide from the reaction of adsorbed water trapped at the InP/Si interface. INTRODUCTION InP and its lattice-matched materials In1-xGaxAsyP1-y are of great technological importance. They find application in high-speed devices and form the basis for semiconductor lasers in the low dispersion and minimum loss wavelength regime of optical fibers at 1.3 and 1.55 µm. Additionally, they are also used in high-efficiency photovoltaics, due to their high internal quantum efficiency. However, InP is brittle, expensive and not available in large sizes. The integration of InP on Si is therefore of great technological interest: By utilizing wafer bonding and layer transfer of thin InP films to Si, InP/Si epitaxial templates could be fabricated, improving the mechanical robustness and reducing the cost of InP devices, while extending the size of InP substrates for improved manufacturing efficiency and enabling integration of Si-based logic devices with optoelectronic and high-speed communications devices. The integration of InP and GaAs on Si would also have a great impact on photovoltaics. Indeed, this would make possible the realization of a four-junction solar cell design consisting of InGaAs, InGaAsP, GaAs and Ga0.5In0.5P subcells. This structure could reach efficiencies of 35.4% at 1xAM0 [1]. We recently demonstrated the integration of optically active InP on Si by wafer bonding [2]. However, a detailed understanding of the evolution of interfacial electrical and structural properties is still needed. In this paper, we present results of such a study. EXPERIMENTAL InP/Si bonded pairs were prepared following our standa
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