Abstract
The integration of III-V semiconductors with silicon is a key issue for photonics, microelectronics and photovoltaics. With the standard approach, namely the epitaxial growth of III-V on silicon, thick and complex buffer layers are required to limit the crystalline defects caused by the interface polarity issues, the thermal expansion, and lattice mismatches. To overcome these problems, we have developed a reverse and innovative approach to combine III-V and silicon: the straightforward epitaxial growth of silicon on GaAs at low temperature by plasma enhanced CVD (PECVD). Indeed we show that both GaAs surface cleaning by SiF4 plasma and subsequent epitaxial growth from SiH4/H2 precursors can be achieved at 175 °C. The GaAs native oxide etching is monitored with in-situ spectroscopic ellipsometry and Raman spectroscopy is used to assess the epitaxial silicon quality. We found that SiH4 dilution in hydrogen during deposition controls the layer structure: the epitaxial growth happens for deposition conditions at the transition between the microcrystalline and amorphous growth regimes. SIMS and STEM-HAADF bring evidences for the interface chemical sharpness. Together, TEM and XRD analysis demonstrate that PECVD enables the growth of high quality relaxed single crystal silicon on GaAs.
Highlights
Silicon is the most widely used material in microelectronics, thanks to its numerous advantages: small mass density, good thermal conductivity, excellent passivation by SiO2, abundance and low cost, non-toxicity, maximum wafer diameter, tremendous amount of research, mature industrial processes, etc
The subsequent hetero-epitaxial growth of silicon on GaAs has been performed in the same plasma enhanced CVD (PECVD) reactor, keeping a constant temperature of 175 °C, with SiH4/ H2 gas precursors
We found that silane dilution was the key parameter for promoting epitaxial growth: high dilution lead to microcrystalline silicon on GaAs, low dilution resulted in amorphous growth while epitaxial growth was observed for intermediate silane dilutions
Summary
Silicon is the most widely used material in microelectronics, thanks to its numerous advantages: small mass density, good thermal conductivity, excellent passivation by SiO2, abundance and low cost, non-toxicity, maximum wafer diameter, tremendous amount of research, mature industrial processes, etc. As GaAs growth is usually performed at high temperature (e.g. 600–700 °C in MOCVD reactors), additional defects appear upon cooling the sample down to room temperature, due to the thermal expansion mismatch with silicon; those defects have deleterious effects on the device properties[15,16]. Another approach being explored to limit the impact of crystal defects is to grow buffer layers between the Si substrate and the active III-V material; it helps to reduce and relax the defects arising from the change of lattice constant. In the field of Photovoltaics, this new approach can be advantageously used to grow inverted III-V(MOCVD)/SiGe(PECVD) multijunctions solar cells[26,27]
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