Wavelength stabilizer for telecommunication lasers: design and optimization

We introduce a novel method for the wavelength stabilization of semiconductor lasers for telecommunications. The approach is based on a wavelength-sensitive photodetector which, in a feedback system, generates an error signal apt to tune the source to the desired value. We extensively investigate the influence of various design parameters on performance figures such as tunability, steady-state error, and temperature dependence, as well as fabrication tolerances. The results are compared with standard specifications for wavelength-division-multiplexed optical communications with various channel spacings.     

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.     

Ge-on-Si approaches to the detection of near-infrared light

We review our recent results on Ge-based near-infrared photodetectors grown on silicon. We fabricated metal-semiconductor-metal photodetectors based on epitaxial pure-Ge grown on silicon by chemical vapor deposition. Material characterization and device performances are illustrated and discussed. Exploiting a novel approach based on evaporation of polycrystalline-Ge on silicon, we also realized efficient near-infrared photodiodes with good speed and sensitivity. Finally, multiple-element devices were designed, fabricated, and tested, such as a voltage-tunable wavelength-selective photodetector based on a SiGe superlattice and a linear array of 16 photodetectors in poly-Ge on Si     

A solid-state near infrared spectrum analyzer based on polycrystalline Ge on Si

We report on a novel solid-state spectrum analyzer in the near infrared. The device is an array of six photodetectors based on polycrystalline germanium film evaporated on a silicon substrate and each element is a wavelength-selective detector. We describe the fabrication and characterization of such device and we demonstrate its capability both as a wavelengthmeter for quasi-monochromatic light beams and as a spectrum analyzer.     

Thermal evaporation of Ge on Si for near infrared detectors: Material and device characterization

Using a low-temperature process, we thermally evaporated Ge thin films on Si substrates and investigated both structural and electrical properties of samples grown at various temperatures. The characterization included X-ray diffraction, atomic force microscopy and Hall measurements and aimed at determining a suitable temperature range in terms of crystal quality and transport properties. Finally, we employed Ge films on Si to fabricate near infrared photodiodes and test them in terms of dark current and responsivity.     

Linear array of Si-Ge heterojunction photodetectors monolithically integrated with silicon CMOS readout electronics

We describe a linear array of Ge-Si heterojunction photodiodes monolithically integrated on a complementary metal-oxide-semiconductor (CMOS) integrated circuit for detection and imaging in the near infrared. Detectors are realized by thermal evaporation of Ge films at the end of the standard CMOS process on substrates held at low temperature (300/spl deg/C). Each of the 64 detectors is connected to a front-end stage for photocurrent integration and analog-to-digital conversion.     

Germanium on insulator near-infrared photodetectors fabricated by layer transfer

We report on novel pn Ge photodetectors fabricated on glass. The fabrication consists of wafer bonding and layer splitting, followed by a low-temperature epitaxial growth of Ge. The photodiodes are characterized in terms of dark current and responsivity, and their performance compared with devices realized on either Ge or Si. The minimum current density is 50 μA/cm² at 1 V reverse bias, the responsivity is 0.2 A/W in the photovoltaic mode, with a maximum of 0.28 A/W at 1.55 μm at a reverse voltage of 5 V.     

A Near-Infrared Digital Camera in Polycrystalline Germanium Integrated on Silicon

We report on the first silicon-integrated 2-D light-sensitive array equipped with complementary-metal-oxide-semiconductor addressing and readout electronics and operating in the near infrared. The chip includes 64 times 8 pixels, 64 analog-to-digital converters, cancellation circuitry for dark current, and facilities for test/calibration. We describe its architecture and fabrication, its electronic and optoelectronic characterization, as well as its operation as a near-infrared camera     

Germanium-on-glass near-infrared detectors

Ge-on-glass photodetectors is fabricated by wafer bonding and layer splitting, followed by the epitaxial growth of pn structures. The detectors exhibit a remarkably low dark current density of 50 muA/cm² at 1 V reverse bias and responsivities as high as 0.33 and 0.43 A/W at 1.52 and 1.3 mum, respectively. This approach can be readily extended to other substrates, enabling the integration of Ge on different platforms.