Integration of GaAs on Ge/Si towers by MOVPE
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Integration of GaAs on Ge/Si towers by MOVPE A. G. Taboada,1 T. Kreiliger,1 C. V. Falub,1 M. Richter,2 F. Isa,3 E. Müller,5 E. Uccelli,2 P. Niedermann,4 A. Neels,4 G. Isella,3 J. Fompeyrine,2 A. Dommann,4 H. von Känel1 1
Laboratory for Solid State Physics, ETH Zürich, Schafmattstr. 16 CH-8093 Zürich, Switzerland IBM Research GmbH, Zurich Research Laboratory, Säumerstrasse 4, CH-8803 Rüschlikon, Switzerland 3 L-NESS and Dipartamento di Fisica-Politecnico di Milano,Via Anzani 42, I-22100 Como, Italy 4 Microsystems Technology, CSEM, Jaquet Droz 1, CH-2002 Neuchâtel, Switzerland 5 Electron Microscopy ETH Zürich (EMEZ), Wolfgang-Pauli-Str. 16, CH-8093 Zürich, Switzerland 2
ABSTRACT We report on the maskless integration of micron-sized GaAs crystals on patterned Si substrates by metal organic vapor phase epitaxy. In order to adapt the mismatch between the lattice parameter and thermal expansion coefficient of GaAs and Si, 2 μm tall Ge crystals were first grown as virtual substrate by low energy plasma enhanced chemical vapor deposition. We investigate the morphological evolution of the GaAs structures grown on top of the Ge crystals at the transition towards full pyramids with energetically stable {111} facets. A substantial release of strain is shown in GaAs crystals with a height of 2 μm and lateral sizes up to 15×15 m2 by both X-ray diffraction and photoluminescence. INTRODUCTION New semiconductor functionalities imply mainstream Si technology to be extended to other semiconducting materials with optical and electrical properties beyond those of Si. In order to exploit the advantages of the III-V/Si system, significant challenges will need to be met. Defects due to the lattice or thermal expansion coefficients mismatch (4.1% and ~ 60 %, respectively at 300 K for GaAs/Si), and anti-phase domains (APDs) must be avoided. Several approaches were attempted in order to optimize the epitaxial integration of GaAs on Si, such as: low temperature nucleation by both metal organic vapor phase epitaxy (MOVPE),1 and molecular beam epitaxy (MBE),2, 3, 4 use of Ge or GeSi virtual substrates,5, 6 and the incorporation of intermediate graded GaAsP or InGaP layers.7 In order to solve the inherent issues related to the integration of GaAs on Si, the most promising III-V/Si combination, we chose to adapt the highly successful concept of 3dimensional (3D) hetero-epitaxy recently reported.8 Our approach involves Ge crystals grown by low energy plasma enhanced chemical vapor deposition (LEPECVD)9 on top of m-sized Si pillars as a substitute for Ge substrates, characterized by a very small lattice mismatch (~0.07%) and comparable thermal expansion coefficients (~15%) with respect to GaAs. Moreover, growth on patterned substrates has additional advantages compared to the planar growth. First, if the crystals exhibit sufficiently large aspect ratios, threading dislocations can escape laterally at the crystal sidewalls. This so-called aspect ratio trapping (ART) mechanism has been previously used for the growth of GaAs and GaAs/Ge epilayers on
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