Selective-Area High-Quality Germanium Growth for Monolithic Integrated Optoelectronics

Selective-area germanium (Ge) layer on silicon (Si) is desired to realize the advanced Ge devices integrated with Si very-large-scale-integration (VLSI) components. We demonstrate the area-dependent high-quality Ge growth on Si substrate through SiO₂ windows. The combination of area-dependent growth and multistep deposition/hydrogen annealing cycles has effectively reduced the surface roughness and the threading dislocation density. Low root-mean-square surface roughness of 0.6 nm is confirmed by atomic-force-microscope analysis. Low defect density in the area-dependent grown Ge layer is measured to be as low as 1 ×10⁷ cm^-2 by plan-view transmission-electron-miscroscope analysis. In addition, the excellent metal-semiconductor-metal photodiode characteristics are shown on the grown Ge layer to open up a possibility to merge Ge optoelectronics with Si VLSI.

I. Introduction

After the development of low-loss and low-dispersion silica fibers, III–V compound lasers, and Ge photodetectors, photonics research has focused on the demonstration of individual devices for wideband and multifunctional optical signal processing [1]. Because the growing photonics market requires more functionality and lower cost, photonic circuitry is desired to be monolithically integrated and to utilize the CMOS processing and low-cost substrates. Germanium and Si CMOS-compatible materials have thus been a natural choice for lower cost platforms [1], [2] and process integration with III–V optoelectronics. Ge emerges as a multifunctional material for the electronic–photonic integration on Si platform, due to its III–V and CMOS compatibility, and direct band-gap energy in the telecommunication wavelengths. The integration of III–V and Ge photonic components onto Si CMOS chips is the shortest route for meeting market expectations.