We present a compact 1.3 × 4 μm2 Germanium waveguide photodiode, integrated in a CMOS compatible silicon photonics process flow. This photodiode has a best-in-class 3 dB cutoff frequency of 45 GHz, responsivity of 0.8 A/W and dark current of 3 nA. The low intrinsic capacitance of this device may enable the elimination of transimpedance amplifiers in future optical data communication receivers, creating ultra low power consumption optical communications.

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and the resistance of small area photodiodes and thereby increases both the available output power and the RC cutoff frequency. A conventional planar avalanche diode with an active area of 10'4 cm2 has a total area of -2.5 x cm2 because of the guard ring, and a series resistance of -50 -100 ohms. Because of the excess capacitance and resistance multiplications of greater than 10 are necessary in order just to equal the available output power of a conventional nonavalanching p-i-n photodiode. The p-nf (n-p-diodes can be designed to have resistances (Rs -2 ohms), capacitances (C < 1 pf), and RC cutoff frequencies (FCo 2 100 GHz) equivalent to those of the p-i-n, and to have uniform multipllcation as well.carrier can be higher in the p-n+ (n-pf ) diode. E.g., a p-nd-Si diode will Quantum efficiencies for the collection of the higher ionization coefficient realize an -20% improvement in electron quantum efficiency at 6328 A when compared to an n+-p diode with a 0.5 micron junction depth.Uniform avalanche photodiodes, without guard rings, have been fabri-Preliminary results are discussed. cated in silicon by a combination of epitaxial and doped oxide processing. mo-electric cooler, amplifier, and biasing circuit is described. The photo-A photodetector consisting of a germanium avalanche photodiode, therdiode is of the graded guardring structure and has an active avalanche region 10 mils in diameter and a depletion width a t break,down at 5.0 Fm. The photodiode is mounted on a single-stage thermoelectric cooler for the purpose of reducing the bulk leakage current. Also mounted on the cold surface is a temperature sensing reference diode used to control the biasing circuit and provide constant avalanche gain in the photodiode. The amplifier was designe'd to be driven with the photodiode current source and provide a voltage output. The amplifier has a 2.6 K ohm transimpedance over the range from 30 kHz to 30 MHz.The NEP of the complete detector was measured for various values of avalanche gain at 25°C and -20°C. The input signal to the diode was 1.15 pm light, 50% modulated at 40 kHz. The noise bandwidth of the completed detector was 39 MHz. At M = l, the case of a conventional photodiode, the measured system NEP of lo-' l watts Hz -E is limited by the amplifier noise. With increasing gain the system NEP decreascd to an optimum of gain at the optimum NEP was 8 and 25 at 25°C. and -2O"C., respectively; for 2.8 x IO-' watts Hzat 25°C and wattsHz-IR at T = -20°C. The gains above the optimum gain the NEP was found to increase.frequency response extending from baseband up through the microwave A static crossed-field photomultiplier can be designed to have a useful high-gain crossed-field photomultiplier with a frequency response extending range.'t2 This paper describes the design and experimental evaluation of a have resulted in a small, relatively lightweight package which can be used to 6 GHz. Permanent magnet focusing and a compact mechanical design outside of the laboratory.throughout the microwave range using cw modulati...