Stephane Demiguel

Recent advances in avalanche photodiodes

Until the early 2000s, the avalanche photodiode (APD) was widely deployed in high-performance optical receivers that operated up to 10 Gb/s. In subsequent years, the use of APDs for high-capacity systems declined as a result of their limited gain bandwidth, the transition to coherent detection, and the development of high-efficiency modulation techniques. Recently, the rapid growth of optical-fiber communications systems that utilize baud rates up to 25 Gb/s represented by a 100-Gb/s Ethernet has led to a resurgence of research on APDs and the development of low-noise APDs with enhanced gain bandwidth. This paper presents a brief review of APD fundamentals and describes some of the recent advances.

High-saturation-current charge-compensated InGaAs-InP uni-traveling-carrier photodiode

Charge compensation is utilized in an InGaAs-InP uni-traveling-carrier photodiode to mitigate the space-charge effect. A 20-/spl mu/m-diameter photodiode achieved a bandwidth of 25 GHz and large-signal 1-dB compression current greater than 90 mA; the output power at 20 GHz was 20 dBm. A smaller /spl sim/100-/spl mu/m/sup 2/ photodiode exhibited a bandwidth of 50 GHz and large-signal 1-dB compression current greater than 50 mA. The maximum RF output power at 40 GHz was 17 dBm.

Very high-responsivity evanescently coupled photodiodes integrating a short planar multimode waveguide for high-speed applications

We report an evanescently coupled photodiode that utilizes a short planar multimode waveguide. Very high responsivity (> 1 A/W) with polarization dependence less than 0.5 dB, 48-GHz bandwidth, and 11-mA saturation current were achieved.

High-saturation current wide-bandwidth photodetectors

This paper describes the design and performance of two wide-bandwidth photodiode structures. The partially depleted absorber photodiode utilizes an absorbing layer consisting of both depleted and undepleted In/sub 0.53/Ga/sub 0.47/As layers. These photodiodes have achieved saturation currents (bandwidths) of >430 mA (300 MHz) and 199 mA (1 GHz) for 100-/spl mu/m-diameter devices and 24 mA (48 GHz) for 100-/spl mu/m/sup 2/ area devices. Charge compensation has also been utilized in a similar, but modified In/sub 0.53/Ga/sub 0.47/As-InP unitraveling-carrier photodiode design to predistort the electric field in the depletion region in order to mitigate space charge effects. For 20-/spl mu/m-diameter photodiodes the large-signal 1-dB compression current and bandwidth were /spl sim/90 mA and 25 GHz, respectively.

High-saturation-current InP-InGaAs photodiode with partially depleted absorber

A high-saturation-current InGaAs photodiode (PD) with a partially depleted absorber is demonstrated. Optical responsivity of 0.58 A/W and over 1.1 W of dissipated electrical power is achieved. Small signal compression current of 110 and 57 mA is measured at radio-frequency bandwidths of 1 and 10 GHz, respectively. This continuous photocurrent is believed to be the highest reported value for a p-i-n InGaAs PD at these bandwidths.

InGaAs/InAlAs avalanche photodiode with undepleted absorber

We report an avalanche photodiode with an undepleted p-type InGaAs absorption region and a thin InAlAs multiplication layer. The motivation for utilizing an undepleted absorption layer, which is similar to that in the unitraveling carrier photodiode, is to reduce the dark current. A dark current below 1 nA at a gain of 10 and a gain–bandwidth product of 160 GHz are demonstrated.

A comparison of front- and backside-illuminated high-saturation power partially depleted absorber photodetectors

A systematic study of high-saturation-current p-i-n In/sub 0.53/Ga/sub 0.47/As photodiodes with a partially depleted absorber (PDA) has been made under front (p-side) and back (n-side) illumination. The photodiode structure consists of an In/sub 0.53/Ga/sub 0.47/As absorption region (450-nm p-InGaAs, 250-nm unintentionally doped InGaAs, and 60-nm n-InGaAs) sandwiched between p- and n-InP layers. For front illumination of a 34-/spl mu/m-diameter photodiode at 2-V bias the saturation currents were 23 and 24 mA at 10 and 1 GHz, respectively. Under similar conditions, backside-illumination resulted in saturation currents of 76 mA (10 GHz) and >160 mA (1 GHz). Backside illumination of a 100-/spl mu/m-diameter photodiode achieved a saturation current >400 mA. For the case of front illumination the device lateral resistance dominates whereas for backside illumination the response is determined primarily by the space charge effect.

Analysis of partially depleted absorber waveguide photodiodes

This paper presents the analysis and characterization of partially depleted absorber (PDA) photodiodes. Coupling to these photodiodes is achieved through a planar short multimode waveguide (PSMW) structure. Electric transport in the PDA structure has been investigated and an equivalent electric circuit was developed. Measurements on 5/spl times/20 /spl mu/m/sup 2/ PSMW PDA photodiodes have shown 0.80 A/W responsivity with a fiber mode diameter as high as 6 /spl mu/m. The transverse electric/transverse magnetic polarization dependence was <0.5/spl plusmn/0.3 dB with -1-dB input coupling tolerances as high as /spl plusmn/2.0 and /spl plusmn/1.3 /spl mu/m for horizontal and vertical directions. The -3-dB bandwidth was 50 GHz, and the -1-dB compression current at 40 GHz was 17 mA corresponding to +4.5 dBm radio frequency (RF) power. Compared to similar evanescently coupled p-i-n photodiodes, the saturation current has been significantly improved while maintaining comparable bandwidth and high responsivity.

Design and demonstration of novel QW intermixing scheme for the integration of UTC-type photodiodes with QW-based components

We present the design and demonstration of unitraveling carrier (UTC) photodiodes fabricated using a novel quantum-well (QW) intermixing and metal-organic chemical vapor deposition (MOCVD) regrowth fabrication platform. The photodiodes discussed here were realized on the same chip as high gain centered QW active regions, intermixed passive centered well waveguides, and low optical confinement offset QW active regions regrown over intermixed wells. This demonstration lifts previous constraints imposed on high functionality photonic circuits, which forced a common waveguide architecture in the detector, laser, and amplifier by validating a platform suited for the monolithic integration of UTC photodiodes into photonic integrated circuits comprised of widely tunable high gain laser diodes, high efficiency modulators, and low optical confinement high saturation power semiconductor optical amplifiers. In this manuscript we focus on the design and performance of UTC photodiodes fabricated on intermixed QWs using this novel scheme. The photodiodes exhibit /spl sim/90% internal quantum efficiency, excellent photocurrent handling capabilities, and minimal response roll-off over the 20 GHz of our testing capability. The 40 Gb/s operation was achieved with the demonstration of open eye diagrams.

High Power Photodiode Wafer Bonded to Si Using Au With Improved Responsivity and Output Power

High power photodiodes wafer bonded to Si using a gold intermediate layer were demonstrated. A fabricated 20-mum-diameter photodiode exhibited a bandwidth of ~18 GHz, a large-signal saturation-current of ~50 mA, and a peak responsivity of ~1 A/W. Both the responsivity and the saturation current of the Au-bonded photodiode were improved compared to the photodiode with the same structure on InP substrate