Gabriel Dehlinger

High-speed Germanium-on-SOI lateral PIN photodiodes

We report the fabrication and characterization of high-speed germanium on silicon-on-insulator lateral PIN photodetectors. At an incident wavelength of 850 nm, 10 /spl times/10-/spl mu/m detectors with finger spacing S of 0.4 /spl mu/m (0.6 /spl mu/m) produced a -3-dB bandwidth of 29 GHz (27 GHz) at a bias voltage of -1 V. The detectors with S=0.6 /spl mu/m had external quantum efficiency of 34% at 850 nm and 46% at 900 nm and dark current of 0.02 /spl mu/A at -1-V bias.

Germanium-on-SOI Infrared Detectors for Integrated Photonic Applications

An overview of recent results on high-speed germanium-on-silicon-on-insulator (Ge-on-SOI) photodetectors and their prospects for integrated optical interconnect applications are presented. The optical properties of Ge and SiGe alloys are described and a review of previous research on SOI and SiGe detectors is provided as a motivation for the Ge-on-SOI detector approach. The photodetector design is described, which consists of lateral alternating p- and n-type surface contacts on an epitaxial Ge absorbing layer grown on an ultrathin-SOI substrate. When operated at a bias voltage of -0.5 V, 10mumtimes10 mum devices have dark current Idark, of only ~10 nA, a value that is nearly independent of finger spacing S, between S=0.3mum and 1.3mum. Detectors with S=1.3mum have external quantum efficiencies eta, of 52% (38%) at lambda=895 nm (850 nm) with corresponding responsivities of 0.38 A/W (0.26 A/W). The wavelength-dependence of eta agrees fairly well with expectations, except at longer wavelengths, where Si up-diffusion into the Ge absorbing layer reduces the efficiency. Detectors with 10 mumtimes10 mum area and S=0.6mum have -3-dB bandwidths as high as 29 GHz, and can simultaneously achieve a bandwidth of 27 GHz with Idark=24 nA, at a bias of only -1 V, while maintaining high efficiency of eta=46%(33%), at lambda=895 nm (850 nm). Analysis of the finger spacing and area-dependence of the device speed indicates that the performance at large finger spacing is transit-time-limited, while at small finger spacing, RC delays limit the bandwidth. Methods to improve the device performance are presented, and it is shown that significant improvement in the speed and efficiency both at lambda=850 and 1300 nm can be expected by optimizing the layer structure design

Ge-on-SOI-Detector/Si-CMOS-Amplifier Receivers for High-Performance Optical-Communication Applications

In this paper, an overview and assessment of high-performance receivers based upon Ge-on-silicon-on-insulator (Ge-on-SOI) photodiodes and Si CMOS amplifier ICs is provided. Receivers utilizing Ge-on-SOI lateral p-i-n photodiodes paired with high-gain CMOS amplifiers are shown to operate at 15 Gb/s with a sensitivity of -7.4 dBm (BER=10-12) while utilizing a single supply voltage of only 2.4 V. The 5-Gb/s sensitivity of similar receivers is constant up to 93 degC, and 10-Gb/s operation is demonstrated at 85 degC. Error-free (BER<10-12) operation of receivers combining a Ge-on-SOI photodiode with a single-ended high-speed receiver front end is demonstrated at 19 Gb/s, using a supply voltage of 1.8 V. In addition, receivers utilizing Ge-on-SOI photodiodes integrated with a low-power CMOS IC are shown to operate at 10 Gb/s using a single 1.1-V supply while consuming only 11 mW of power. A perspective on the future technological capabilities and applications of Ge-detector/Si-CMOS receivers is also provided

A 15-Gb/s 2.4-V Optical Receiver Using a Ge-on-SOI Photodiode and a CMOS IC

We report the fastest (15 Gb/s) and lowest voltage (2.4V) all-silicon-based optical receiver to date. The receiver consists of a lateral, interdigitated, germanium-on-silicon-on-insulator (Ge-on-SOI) photodiode wire-bonded to a 0.13-mum complementary metal-oxide-semiconductor (CMOS) receiver integrated circuit (IC). The photodiode has an external quantum efficiency of 52% at lambda=850 nm and a dark current of 10 nA at -2 V. The small-signal transimpedance of the receiver is 91-dBOmega and the bandwidth is 6.6 GHz. At a bit-error rate of 10-12 and lambda=850 nm; the receiver exhibits sensitivities of -11.0, -9.6, and -7.4 dBm at 12.5, 14, and 15 Gb/s, respectively. The receiver operates error-free at rates up to 10 Gb/s with an IC supply voltage as low as 1.5 V and with a photodiode bias as low as 0.5 V. The power consumption is 3 to 7 mW/Gb/s. The Ge-on-SOI photodiode is well suited for integration with CMOS processing, raising the possibility of producing high-performance, low-voltage, monolithically integrated receivers based on this technology in the future

Temperature-Dependent Analysis of Ge-on-SOI Photodetectors and Receivers

The temperature dependence of dark current and receiver performance for Ge-on-SOI photodiodes is presented. Error-free receiver operation at 10 Gb/s is achieved at 85degC despite a 10x increase in dark current compared to room temperature

High-efficiency, Ge-on-SOI lateral PIN photodiodes with 29 GHz bandwidth

Ge has tremendous potential for high-speed operation at /spl lambda/=850 nm, an important wavelength for short range highly-parallel interconnects, because the absorption length of Ge is only a few hundred nm. However, for thin Ge-on-Si detectors, the Ge film must be isolated from the underlying Si in order to prevent collection of slow carriers generated deep within the substrate. In this work, we present results of lateral PIN photodetectors fabricated using Ge films deposited on ultra-thin silicon-on-insulator (SOI) substrates. These devices have bandwidths as high as 29 GHz, and the highest bandwidth-efficiency product reported to date for a group-IV photodetector.

High speed, lateral PIN photodiodes in silicon technologies

High speed, efficient photodetectors are difficult to fabricate in standard silicon fabrication processes due to the long absorption length of silicon. However, high performance servers will soon require dense optical interconnects with low cost and high reliability, and this trend favors monolithic silicon receivers over hybrid counterparts. Recently, lateral PIN photodiode structures have been demonstrated in silicon CMOS technology with little or no process modifications. Optical receivers based on these detectors have achieved record performance in terms of speed and sensitivity. This paper will discuss the advantages, issues and recent advances in silicon-based photodetectors and optical receivers. This includes the fastest photodetector ever implemented in a standard bulk CMOS process, a 13.9 Gb/s lateral trench detector implemented in a modified EDRAM process, and a >15 GHz pure germanium photodiode grown directly on a silicon substrate.

A 17-Gb/s low-power optical receiver using a Ge-on-SOI photodiode with a 0.13-&#956;m CMOS IC

We report the fastest (17Gb/s) and lowest-voltage (1.8V) all-silicon CMOS optical receiver to date, based on a germanium-on-SOI photodiode. The 12.5-Gb/s sensitivity at 850nm is -12.7dBm (BER=10-12), with a power consumption as low as 50mW.

High-speed germanium-on-insulator photodetectors

We will present recent results from our work on germanium-on-silicon photodetectors. We demonstrate that the devices display high bandwidth and efficiency at 850 nm, and could be suitable for future 40 Gb/sec optical interconnect applications.

High-speed, low-voltage optical receivers consisting of Ge-on-SOI photodiodes paired with CMOS ICs

Silicon-based, monolithically-integrated optical receivers offer the potential of lowering the cost of optical interconnects through simplified packaging and leveraging established Si-manufacturing technology, in addition to enabling new applications such as inter- and intra-chip optical links that will require large-scale receiver arrays. Silicon photodetectors have progressed, and integrated receivers have been demonstrated to operate above 10 Gb/s; however, the poor efficiency of silicon in detecting 850-nm light results in fundamental tradeoffs in performance and/or operating voltage. In contrast, using Ge as the detector material opens the possibility of producing fast, efficient, and low-voltage photodiodes compatible with CMOS processing. We have fabricated planar, interdigitated Ge-on-SOI photodiodes in Ge absorption layers grown directly on SOI wafers. Devices with 10 x 10 μm2 square active areas, biased at -2 V, with an electrode spacing of 0.6 to 0.8 μm, exhibit dark currents less than 10 nA, bandwidths in excess of 23 GHz, and external quantum efficiencies of 52 % (0.35 A/W) at a wavelength of 850 nm. We have built and characterized three different optical receivers using 0.13-μm CMOS ICs: 1) a 15-Gb/s high-gain full receiver (transimpedance amplifier, limiting amplifier, and output driver); 2) a 10-Gb/s, low-power full receiver (powered by a single 1.1-V supply); 3) a 19-Gb/s high-speed receiver front-end (transimpedance amplifier only). These receivers achieve the highest operating speed, highest sensitivity at > 10 Gb/s rates, lowest-voltage single-supply operation, and lowest power consumption for any all-silicon-based receivers reported to-date, and illustrate the performance that can be attained through combining Ge detectors with CMOS analog circuitry.