M. Jutzi

Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth

Vertical-incidence Germanium photodiodes grown on thin strain-relaxed buffers on Silicon substrates are reported. For a mesa-type detector with a diameter of 10 /spl mu/m, a resistance-capacitance-limited 3-dB bandwidth of 25.1 GHz at an incident wavelength of 1552 nm and zero external bias has been measured. At a reverse bias of 2 V, the bandwidth is 38.9 GHz. The detector comprises a 300-nm-thick intrinsic region, and thus, has the potential for easy integration with Si circuitry and exhibits zero bias external quantum efficiencies of 23%, 16%, and 2.8% at 850, 1298, and 1552 nm, respectively.

High bandwidth Ge p-i-n photodetector integrated on Si

The authors present a germanium on silicon p-i-n photodiode for vertical light incidence. For a Ge p-i-n photodetector with a radius of 5μm a 3dB bandwidth of 25GHz is measured at an incident wavelength of 1.55μm and zero external bias. For a modest reverse bias of 2V, the 3dB bandwidth increases to 39GHz. The monolithically integrated devices are grown on Si with solid source molecular beam epitaxy. The complete detector structure consisting of a highly p-doped Ge buried layer, an intrinsic absorption region, and a highly n-doped top contact layer of Ge∕Si is grown in one continuous epitaxial run. A low growth temperature sequence was needed to obtain abrupt doping transitions between the highly doped regions surrounding the intrinsic layer. A theoretical consideration of the 3dB bandwidth of the Ge detector was used to optimize the layer structure. For a photodiode with 5μm mesa radius the maximum theoretical 3dB frequency is 62GHz with an intrinsic region thickness of 307nm.

2-gb/s CMOS optical integrated receiver with a spatially Modulated photodetector

A monolithically integrated optical receiver fabricated in an unmodified 0.18-/spl mu/m silicon complementary metal-oxide-semiconductor technology is presented. The receiver features a spatially modulated photodetector to suppress slow diffusion tails. The receiver circuit comprises a transimpedance amplifier, a limiting amplifier, and an output buffer. At 2 Gb/s and an incident wavelength of 850 nm, a receiver sensitivity of -8 dBm at a bit-error rate of 10/sup -9/ has been achieved.

High Ge content photodetectors on thin SiGe buffers

Abstract PIN SiGe photodetectors (PD) are grown by MBE with Ge contents x =0, 0.10, 0.2, 0.27 and 0.5. For PDs with high Ge content, which are grown beyond the SiGe layer critical thickness, thin (sub 100 nm) strain relaxed, p + (B)-doped SiGe buffers are of special importance. The layer structure of the samples consists of a 5×10 18 cm −3 p + (B)-doped buffer layer as a bottom contact, followed by a 300 nm intrinsic active zone covered with a 3×10 20 cm −3 n ++ (Sb)-doped top contact layer. Extremely low temperatures (LT) during the first growth stage of the SiGe buffers are implemented. Process windows for high strain relaxation on different substrates are determined. The role of growth conditions in crystal structure formation is in situ monitored by time resolved reflectivity (TRR) measurements. For comparison, pseudomorphic PDs and that on conventional graded buffers were also realised. Secondary ion mass spectrometry (SIMS), μ-Raman-spectroscopy and energy dispersive X-ray (EDX) analysis are performed to measure Ge content, composition profiles and degree of relaxation. The microstructure is characterised by cross-section transmission electron microscopy (XTEM). By optical microscopy with Nomarski differential interference contrast (NIC) combined with defect etching technique, typical defects in the layers were studied. Electrical measurements are performed to determine the different current components. The DC current–voltage characteristics show a distinct diode ‘s behaviour of the detectors, which are optically characterised in terms of reverse current for different incident wavelengths.

Ge-on-Si pin-photodiodes for vertical and in-plane detection of 1300 to 1580 nm light

Ge-on-Si pin-photodiodes for vertical and in-plane detection are presented. The devices are grown on an 31 nm ultrathin, strain relaxed buffer (SRB) layer. The vertical photodiode exhibits a zero-bias responsivity of 117 mA/W and a bandwidth of 1.5 GHz at a wavelength of 1298 nm. In comparison, the detector for in-plane detection has a zero-bias responsivity of 70 mA/W and a bandwidth of 4.4 GHz. For a bias voltage of -2 V a bandwidth of 6.2 GHz has been measured. At 1580 nm the photo responsivity of the lateral photodiode is higher (26 mA/W) than of the vertical photodiode (19 mA/W). The dislocation density probably may limit the bandwidth.

SiGe pin-photodetectors integrated on silicon substrates for optical fiber links

100% Ge pin-photodetectors grown on SiGe strain relaxed buffer (SRB) layers are presented, For integrated detectors the SRB layer growth as well as the subsequent SiGe photodiode technology processing must be compatible with standard CMOS technology. DC photoresponsivities of 145 mA/W at 1.3 /spl mu/m and 25 mA/W at 1.55 /spl mu/m can be achieved. In first experiments the 100% Ge pin-photodetector exhibits an RC limited 3-dB opto-electrical bandwidth of 0.9 GHz.

Fast Ge p-i-n Photodetectors on Si

We report about a top-side illuminated Ge photodetector, which is appropriate for transmission of high-speed data at infrared telecommunication wavelengths and is monolithically integrated on a standard Si substrate (Jutzi et al., 2005) for 1552 nm operation. A 3-dB-bandwidth of 38.9 GHz is achieved for a 10 mum diameter detector and a reverse bias of 2 V. These results demonstrate the potential of SiGe photodiodes for Si based optical links at data rates up to 40 Gbit/s and beyond