InP / Si substrates were fabricated through wafer bonding and helium-induced exfoliation of InP, and InGaAs solar cells lattice matched to bulk InP were grown on these substrates using metal-organic chemical-vapor deposition. The photovoltaic characteristics of the InGaAs cells fabricated on the wafer-bonded InP / Si substrates were comparable to those synthesized on commercially available epiready InP substrates, thus providing a demonstration of wafer-bonded InP / Si substrates as an alternative to bulk InP substrates for solar cell applications.

Hydrogen-induced exfoliation combined with wafer bonding has been used to transfer ϳ600-nm-thick films of ͑100͒ InP to Si substrates. Cross-section transmission electron microscopy ͑TEM͒ shows a transferred crystalline InP layer with no observable defects in the region near the bonded interface and an intimately bonded interface. InP and Si are covalently bonded as inferred by the fact that InP/Si pairs survived both TEM preparation and thermal cycles up to 620°C necessary for metalorganic chemical vapor deposition growth. The InP transferred layers were used as epitaxial templates for the growth of InP/In 0.53 Ga 0.47 As/InP double heterostructures. Photoluminescence measurements of the In 0.53 Ga 0.47 As layer show that it is optically active and under tensile strain, due to differences in the thermal expansion between InP and Si. These are promising results in terms of a future integration of Si electronics with optical devices based on InP-lattice-matched materials. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1637429͔Applications of InP-based materials are numerous, and thus integration of InP on Si may enable realization of powerful integrated III-V-on-Si systems. InP and its lattice matched quaternary counterpart In 1Ϫx Ga x As y P 1Ϫy are direct gap semiconductors, which have high carrier mobilities, therefore finding applications in lasers, multijunction solar cells 1 and high-speed devices. Additionally, they cover the low dispersion and minimum loss wavelengths for optical fiber communication at 1.3 and 1.5 m, respectively, making them attractive materials for fabricating semiconductor lasers and detectors for telecommunications applications. However, InP is mechanically fragile, is not available in large substrates, and is expensive. Integrating InP thin films on Si substrates improves its mechanical strength and may also allow InP integration on large substrates by a process of tiling transferred thin films. Most importantly, a viable approach to InP/Si may enable cost-effective integration of infrared optoelectronic devices with well-established silicon electronics.Because InP and Si have a large lattice mismatch ͑8.1%͒, heteroepitaxial growth on Si has not yet been able to produce the high quality electronic material needed in optoelectronic devices, since the dislocation density is typically 10 7 cm 2 . 2In some cases densities of 10 5 cm Ϫ2 can be reached by conformal growth, but this is only possible on very small areas. 3 Other methods have been attempted to circumvent the restrictions of heteroepitaxial growth. However, most of these processes require an entire substrate to be consumed. 4 Direct wafer bonding of III-V semiconductors to Si has been previously demonstrated. 5,6 However, it would be more desirable to have a method for InP/Si integration in which the InP substrate can be repeatedly reused, rather than consuming one InP substrate per active InP-based device layer. Hydrogen-induced exfoliation and layer transfer has shown to be a successful method for Si film fabrication, ...

The role of hydrogen in the exfoliation of Ge is studied using cross-sectional transmission electron microscopy, atomic force microscopy, and multiple-internal transmission mode Fourier-transform infrared absorption spectroscopy and compared with the mechanism in silicon. A qualitative model for the physical and chemical action of hydrogen in the exfoliation of these materials is presented, in which H-implantation creates damage states that store hydrogen and create nucleation sites for the formation of micro-cracks. These micro-cracks are chemically stabilized by hydrogen passivation, and upon annealing serve as collection points for molecular hydrogen. Upon further heating, the molecular hydrogen trapped in these cracks exerts pressure on the internal surfaces causing the cracks to extend and coalesce. When this process occurs in the presence of a handle substrate that provides rigidity to the thin film, the coalescence of these cracks leads to cooperative thin film exfoliation. In addition to clarifying the mechanism of H-induced exfoliation of single-crystal thin Ge films, the vibrational study helps to identify the states of hydrogen in heavily damaged Ge. Such information has practical importance for the optimization of H-induced layer transfer as a technological tool for materials integration with these materials systems.

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The motion and bonding configurations of hydrogen in InP are studied after proton implantation and subsequent annealing, using Fourier transform infrared ͑FTIR͒ spectroscopy. It is demonstrated that, as implanted, hydrogen is distributed predominantly in isolated pointlike configurations with a smaller concentration of extended defects with uncompensated dangling bonds. During annealing, the bonded hydrogen is released from point defects and is recaptured at the peak of the distribution by free internal surfaces in di-hydride configurations. At higher temperatures, immediately preceding exfoliation, rearrangement processes lead to the formation of hydrogen clusters and molecules. Reported results demonstrate that the exfoliation dynamics of hydrogen in InP and Si are markedly different, due to the higher mobility of hydrogen in InP and different implant-defect characteristics, leading to fundamental differences in the chemical mechanism for exfoliation.

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A four-junction cell design consisting of InGaAs, InGeAsP, GaAs, and GaoslnosP subcells could reach 1xAMO efficiencies of 35.4%. but relies on the integration of nonlattice-matched materials. Wafer bonding and layer transfer processes show promise in the fabrication of InP/Si epitaxial templates for growth of the bottom InGaAs and InGaAsP subcells on a Si support substrate. Subsequent wafer bonding and layer transfer of a thin Ge layer onto the lower subcell stack can serve as an epitaxial template for GaAs and GaoslnosP subcelis. Present results indicate that optically active iliN compound semiconductors can be grown on both Ge/Si and InP/Si heterostructures. Currenk voltage electrical characterization of the interfaces of these structures indicates that both lnP/Si and Ge/Si interfaces have specific resistances lower than O.lncmz for heavily doped wafer bonded interfaces, enabling back surface power extraction from the finished cell structure.

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