GeSi based photodetectors and avalanche photodetectors on silicon photonics platform have been widely studied in the
past decade due to its low cost nature and compatibility with CMOS fabrication process. Conventionally, high-quality Ge
on Si is obtained by a direct epitaxy growth or by a wafer/die bonding technique, which complicates the possible on-chip
integration with CMOS electronics such as transimpedance amplifier, equalizer and limiting amplifier etc. Recently,
rapid-melt growth of Ge on insulator emerged as a new method to produce high-quality Ge stripes. In this paper, we
present our effort in making waveguide based photodetectors and avalanche photodetectors using Ge rapid-melt growth.
First, we demonstrate a high-performance, high-speed GeSi heterojunction photodiode by a self-aligned microbonding
technique utilizing surface tension. Such a method is subsequently extended to fabricate a novel butt-coupled, high-speed
metal-semiconductor-metal Ge photodetector. At the same time, we study the possibility of operating GeSi avalanche
photodetectors at a low bias voltage to be compatible with standard CMOS IC power supply. Based on the theoretical
and numerical results, a new type of GeSi avalanche photodetector in three-terminal configuration is proposed and
demonstrated, reaching the lowest possible operation bias voltage constrained by Zener tunneling breakdown.
This paper describes single photon detection for Ge on Si separate-absorption-charge-multiplication (SACM) avalanche
photodiodes and advances in quenching for InP/InGaAs single photon avalanche diodes.
In this paper we present a separate-absorption-charge-multiplication Ge/Si avalanche photodiode, which has a
high gain-bandwidth product (e.g., >860GHz at a wavelength of 1310nm). Such a high gain-bandwidth product is
attributed to the peak enhancement of the frequency response at the high frequency range. From a small signal analysis,
we establish an equivalent circuit model which includes a capacitance parallel connected with an inductance due to the
avalanche process. When the APD operates at high bias voltages, the LC circuit provides a resonance in the avalanche,
which introduces a peak enhancement.
Avalanche Photodiodes (APDs) are widely used in fiber-optic communications as well as imaging and sensing
applications where high sensitivities are needed. Traditional InP-based APD receivers typically offer a 10 dB
improvement in sensitivity up to 10 Gb/s when compared to standard p-i-n based detector counterparts. As the data rates
increase, however, a limited gain-bandwidth product (~100GHz) results in degraded receiver sensitivity. An increasing
amount of research is now focusing on alternative multiplication materials for APDs to overcome this limitation, and one
of the most promising is silicon. The difficulty in realizing a silicon-based APD device at near infrared wavelengths is
that a compatible absorbing material is difficult to find. Research on germanium-on-silicon p-i-n detectors has shown
acceptable responsivity at wavelengths as long as 1550 nm, and this work extends the approach to the more complicated
APD structure. We are reporting here a germanium-on-silicon Separate Absorption Charge and Multiplication (SACM)
APD which operates at 1310 nm, with a responsivity of 0.55A/W at unity gain with long dark current densities. The
measured gain bandwidth product of this device is much higher than that of a typical III-V APD. Other device
performances, like reliability, sensitivity and thermal stability, will also be discussed in this talk. This basic
demonstration of a new silicon photonic device is an important step towards practical APD devices operating at 40 Gb/s,
as well as for new applications which require low cost, high volume receivers with high sensitivity such as imaging and
Research and development on silicon-based optoelectronic devices is increasing as the need for integrated optical
devices is becoming more apparent. One component which has seen rapid performance improvement over the last five
years has been a Ge-on-Si photodetector which can operate between 850 and 1600 nm with high quantum efficiencies
and bandwidths. We have reported on three types of these detectors; normal incident illuminated p-i-n detectors,
waveguide p-i-n detectors, and avalanche photodetectors (APDs). The former has achieved -14.5 dBm sensitivity at 10
Gb/s and 850 nm, which is comparable to similarly commercially packaged GaAs devices. Waveguide photodetectors
have achieved bandwidths of approximately 30 GHz at 1550 nm with internal quantum efficiencies of 90%. Normal
incident avalanche photodetectors operating at 1310 nm have achieved a primary responsivity of 0.54 A/W with a 3-dB
bandwidth of 9GHz at a gain of 17.
This paper presents a physical model for dark count rate and single-photon quantum efficiency of single-photon avalanche photodiodes. The model makes direct connections between the performance of single photon avalanche detectors and the physical parameters of the devices, which are useful for choosing commercial APDs to function in single-photon mode, designing APDs specifically for single-photon detection, and setting up suitable device operation conditions for optimal performance. Good agreement between the calculations and the experimental data from commercial InGaAs/InP APDs validates the model.
We report here on wafer-bonded InGaAs/Si avalanche photodiodes (APDs) demonstrating very low excess noise factors that were fabricated using a high-yield, wafer-scale bonding process. The bonding interface quality was evaluated using high-resolution x-ray diffraction and dark current measurements. Measured dark currents on 20 μm diameter mesas are 25 nA and 170 nA at gains of 10 and 50, respectively. Low excess noise factors, which are predicted due to the superior noise properties of Si as a multiplication layer, were measured to be more than 3 times lower than commercial InGaAs/InP APDs at a gain of 10, and more than 9 times lower at a gain of 50. The corresponding electron/hole ionization coefficient ratio k in these devices is as low as 0.02.
Wafer-bonded avalanche photodiodes (APDs) combining InGaAs for the absorption layer and silicon for the multiplication layer have been fabricated. The reported APDs have a very low room-temperature dark current density of only 0.7 mA/cm2 at a gain of 10. The dark current level is as low as that of conventional InGaAs/InP APDs. High avalanche gains in excess of 100 are presented. The photodiode responsivity at a wavelength of 1.31 micrometers is 0.64 A/W, achieved without the use of an anti-reflection coating. The RC-limited bandwidth is 1.45 GHz and the gain-bandwidth product is 290 GHz. The excess noise factor F is much lower than that of conventional InP-based APDs, with values of 2.2 at a gain of 10 and 2.3 at a gain of 20. This corresponds to an effective ionization rate ratio keff as low as 0.02. The expected receiver sensitivity for 2.5 Gb/s operation at (lambda) = 1.31 um using our InGaAs/silicon APD is -41 dBm at an optimal gain of M = 80.
Analog-to-digital converters operating at unprecedented speeds and resolutions are presently under development using a combination of photonics and electronics techniques. These systems impose stringent performance constraints on the photoreceivers used for photonic - electronic conversion, particularly in regard to linearity and noise. Photodetectors must accommodate optical pulses with very high input powers iwthout saturation, and the pulse input energy must be accurately determined. This paper presents design considerations and simulations of photodetectors and associated preamplifiers to meet these goals.
High performance photodiodes are essential for photonic insertion into Phased Array Antenna Systems. This paper discusses the RF linearity performance of photodiodes with consideration of thermal effect at high photocurrent, and presents new understandings of both surface-normal and waveguide photodiodes using an equivalent circuit model analysis. The analysis is accompanied by a novel diagnostic technique for robust examination of photodiodes.