The invention relates to the field of photodetectors, and in particular to monolithically integrated Ge photodetectors on Si.
Photodetectors are fundamental devices that convert optical signals into electric signals. Fiber optical communication employs 1300 and 1550 nm wavelengths because of low attenuation coefficients of silica fibers. Er doped fiber amplifiers emphasize the importance of 1550 nm because of the direct amplification of optical signals without converting to electric signals. The amplification range between 1530-1560 nm is referred to as C-band, and the recently extended amplification range between 1570-1608 nm is referred to as L-band. The photodetectors for 1550 nm detection have so far been InGaAs photodetectors, since InGaAs is a direct semiconductor whose bandgap is 0.75 eV (corresponding to 1653 nm). Thus, InGaAs photodetectors can convert any optical signal in the C- and L-bands to electric signals. These optical fiber communication components are well developed.
Recently, optical technology has expanded its territory from fiber communication to photonic integrated circuits on a chip. This allows for high speed and broad band communication. The impact is even larger if optics is merged into Si LSIs, e.g., 10 GHz clock processors, etc. InGaAs photodetectors are not easy to implement on a silicon chip, since InGaAs is a III-V compound semiconductor. In general, the elements In, Ga, and As are all dopants in silicon to show donor or acceptor characteristics and could thus alter the circuit performance if diffused. Ge can be a candidate for on-chip photodetectors, since Ge is in the group IV element and produces no harmful effects if diffused. Thus, Ge provides a perfect opportunity to form highly efficient photodetectors.
According to one aspect of the invention, there is provided a photodetector device. The photodetector device includes a plurality of Ge epilayers that are grown on a silicon substrate and annealed in a defined temperature range. The Ge epilayers form a tensile strained Ge layer that allows the photodetector device to operate efficiently in the C-band and L-band.
According to another aspect of the invention, there is provided a method of forming a photodetector device. The method includes forming a plurality of Ge epilayers that are grown on a substrate. Moreover, the method includes annealing the Ge epilayers in a defined temperature range. Furthermore, the method includes developing a tensile strained Ge layer using the annealed Ge epilayers, the tensile strained Ge layer allowing the photodetector device to operate efficiently in the C-band and L-band.
According to another aspect of the invention, there is provided a photodetector device. The photodetector device includes a plurality of SiGe epilayers that are grown on a substrate at a high temperature so as to form a SiGe structure. The SiGe layer forms a tensile strained SiGe layer by cooling to room temperature the SiGe structure using the bi-metal effect. The tensile strained SiGe layer allows the photodetector device to operate efficiently in the C-band and L-band.
According to another aspect of the invention, there is provided a method of forming a photodetector device. The method includes growing a plurality of SiGe epilayers on a silicon substrate at a high temperature so as to form a SiGe structure. Furthermore, the method includes forming a tensile strained SiGe layer by cooling to room temperature the SiGe structure using the bi-metal effect. The tensile strained SiGe layer allows the photodetector device to operate efficiently in the C-band and L-band.