Material and optical properties of GaAs grown on (001) Ge/Si pseudo-substrate
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Material and optical properties of GaAs grown on (001) Ge/Si pseudo-substrate Yves Chriqui1, Ludovic Largeau1, Gilles Patriarche1, Guillaume Saint-Girons1, Sophie Bouchoule1, Daniel Bensahel2, Yves Campidelli2, Olivier Kermarrec2, Isabelle Sagnes1 1 Laboratoire de Photonique et Nanostructures, LPN-CNRS / UPR 20, Route de Nozay, F-91460 Marcoussis FRANCE 2 STMicroelectronics, 850 Rue Jean Monnet, F-38926 Crolles Cedex FRANCE ABSTRACT One of the major challenges during recent years was to achieve the compatibility of III-V semiconductor epitaxy on silicon substrates to combine opto-electronics with high speed circuit technology. However, the growth of high quality epitaxial GaAs on Si is not straightforward due to the intrinsic differences in lattice parameters and thermal expansion coefficients of the two materials. Moreover, antiphase boundaries (APBs) appear that are disadvantageous for the fabrication of light emitting devices. Recently the successful fabrication of high quality germanium layers on exact (001) Si by chemical vapor deposition (CVD) was reported. Due to the germanium seed layer the lattice parameter is matched to the one of GaAs providing for excellent conditions for the subsequent GaAs growth. We have studied the material morphology of GaAs grown on Ge/Si PS using atomic layer epitaxy (ALE) at the interface between Ge and GaAs. We present results on the reduction of APBs and dislocation density on (001) Ge/Si PS when ALE is applied. The ALE allows the reduction of the residual dislocation density in the GaAs layers to 105 cm-2 (one order of magnitude as compared to the dislocation density of the Ge/Si PS). The optical properties are improved (ie. increased photoluminescence intensity). Using ALE, light emitting diodes based on strained InGaAs/GaAs quantum well as well as of In(Ga)As quantum dots on an exactly oriented (001) Ge/Si pseudo-substrate were fabricated and characterized. INTRODUCTION For the past twenty years, many research groups [1] worked on the integration of III-V semiconductors with silicon-based integrated circuits. The wide range of applications, from low cost solar cells to fast clock signal distribution and optical interconnects, is very attractive. However, the lattice mismatch and difference in thermal expansion coefficients between GaAs and Si lead to high dislocation densities (>108 cm-2) [2] and cracks in the epitaxial layer, resulting in low quality materials. Recently, an approach using relaxed Ge/Si1-xGex graded buffer layers has been proposed for the successful monolithic growth of GaAs on Si. The reduced lattice mismatch (0.07% at 300K) due to the Ge layer enabled the realisation of GaAs/AlGaAs and InGaAs/GaAs quantum well laser diodes grown on 6° offcut Ge/Si1-xGex/Si pseudosubstrates (PS) [3,4]. The PS was misoriented to overcome the additional problem of antiphase boundary (APB) formation when growing polar (GaAs) on non-polar (Ge) material [5]. However, the compatibility with Si-CMOS microlectronics systems requires the use of exactly (001) oriented substra
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