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The project ICT-MARISE is aiming at the demonstration of avalanche photodiodes as will be needed from applications (broadband access, 40Gb/s transmission and quantum cryptography) requiring high-sensitivity and large-bandwidth. Two large band-gap III-V materials of interest have made significant progress: AlGaAs and AlInAs, lattice-matched to GaAs and InP, respectively. In MARISE, it is proposed to develop engineered APD structures to benefit from their promising characteristics, while allowing absorption at wavelengths of interest, between 1.3 and 1.6m.
Owing to the use of these materials, the objectives of this project are to push the limits of currently available APDs in two directions: speed and low noise.

In MARISE, three major objectives have been identified:

Objective 1: 1.3 - 1.55 m AlInAs back-illuminated APDs with Gain x Bandwidth of 160 GHz and a dark current < 10 nA @ multiplication factor of 10.
While many laboratories demonstrated APDs with gain-bandwidth product of 100GHz, it is a real challenge to achieve simultaneously a low associated dark current which in case of avalanche photodiodes is linked to material growth and progress in processing technology. Following an accurate material optimisation (calibration of the shield charge doping,...) and an adapted SiNx passivation layer, MARISE objective 1 was achieved with the following APD characteristics: Responsivity of 0.9A/W (at M=1), a total dark current of 8.3nA at M=10, a low excess noise factor F(M=10)=3.3 and a gain-bandwidth product of 160GHz.

Objective 2: 1.55 m AlInAs waveguide APDs with a Gain x Bandwidth product of 200 GHz and a bandwidth > 30 GHz.
In order to achieve an APD operating at 40Gb/s, a waveguide structure is necessary to increase quantum efficiency and large f3dB bandwidth. Reaching such a photodiode with a large gain-bandwidth product is a real challenge since the avalanche layer should be thinned to reduce avalanche built-up time. Major progress toward this objective has been made during the second year of the project mainly through optical waveguide design and optimisation of a very thin APD structure which demonstrated very recently a record 240GHz gain-bandwidth product.

Objective 3: 1.3 m AlGaAs/InGaAsN SAGM Avalanche Photodiode with a targeted Gain x Bandwidth product > 200 GHz.
A major focus of MARISE is the combination of the very promising AlGaAs avalanche material and InGaAsN absorber compatible with telecom wavelengths. Mastering of critical InGaAsN 1.3m material absorber properties was achieved using appropriate growth conditions to reduce background doping and dark current densities <0.14mA/cm at 150kV/cm, in line with MARISE target, were demonstrated.Objectives 1 & 2 are carried out in all work-packages, while objective 3 based on a more challenging avalanche structure is supported by WP1, WP2 and WP3.