>Monolithic CMOS-compatible AlGaInP visible LED arrays on silicon on lattice-engineered substrates (SOLES)
Monolithic CMOS compatible AlGaInP visible LED arrays have been demonstrated on a novel platform called silicon on lattice-engineered substrate (SOLES). SOLES wafers are based on SiGevirtual substrate technology and are suitable for the practical fabrication of SOI CMOS circuits and III–V-based optoelectronic devices on a common silicon substrate. A combination of oxide–oxide wafer bonding and hydrogen-induced exfoliation was used to transfer a thin layer of device-quality silicon on insulator on the top of the SiGe buffers graded to 100% Ge to realize SOLES. Epitaxial layers of a double heterojunction AlGaInP LED emitting near the red region of the visible spectrum (λ = 671 nm) were grown by MOCVD on SOLES wafers using a patterned oxide hard mask. CMOS compatibility was achieved by accessing the n-GaAs cathode of the LED through the underlying n-Ge layer of the SiGe graded buffer rather than etching through the LED stack. The LED was capped with Si to avoid exposing CMOS tools to III–V materials during processing. The Si anode and Ge cathode of the resulting LED structure were contacted using Ti/Al CMOS compatible metallurgy. The prototype array is an important step towards the realization of monolithically integrated optical interconnects in high speed digital systems.
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