The properties of luminescence coupling (LC) in multijunction solar cells were investigated in three-terminal InGaP//InGaAsP and InGaP/GaAs//InGaAsP tandem solar cells fabricated using the bonding technique through metal nanoparticle (MNP) arrays, where // denotes the mechanical stacking using MNP arrays. Power extraction in the three-terminal tandem solar cells is evaluated, showing that the power extraction in the devices is equivalent to a sum of the power extraction of the top and bottom subcells. In addition, the properties of the LC effect are investigated in the three-terminal tandem devices. The LC current increases with the illuminated light intensity and shows a bias-voltage dependency of the subcell that is emitting luminescence. We also discuss the impact of LC on the power extraction of the three-terminal tandem solar cells.
We developed a nano-photodiode that confines and absorbs the sub-wavelength-size optical near field in small-scale
silicon. A surface plasmon resonance antenna is used to enhance the near field in silicon. The response time of the nanophotodiodes
is shorter than that of conventional photodiodes because the separation between anode and cathode and the
size of the electrodes can be as small as one thousandth of that for conventional photodiodes. The full-width at halfmaximum
of the impulse response of the silicon nano-photodiode was as fast as ~20 ps even when the bias voltage was
less than 1 V. This nano-photodiode technology can be applied to other semiconductor materials such as germanium and
ternary compound semiconductors.
Two types of waveguide photodiodes (WG-PD) - an evanescently coupled photodiode (EC-PD) and a separated-absorption-and-multiplication avalanche photodiode (SAM-APD) - have been developed for use in 40-Gbps receivers. The EC-PD simultaneously exhibited high external responsivity of 0.96 A/W and wide bandwidth of >40 GHz. The SAM-APD showed wide bandwidth of 30-35 GHz and gain-bandwidth (GB) product of 140-180 GHz. High receiver sensitivities of -11.3 dBm at 43 Gbps and -19 dBm at 40 Gbps have been successfully achieved for the EC-PD and the SAM-APD, respectively.
An evanescently coupled waveguide photodiode (EC-WG-PD) for both 1310-nm and 1550-nm wavelength bands has been developed for use in long-haul and high capacity very-short-reach (VSR) transmission systems. The EC-WG-PD is much more robust than a conventional waveguide photodiode (WG-PD) under high optical input operation because its absorbed optical power density is distributed along the light propagation in the waveguide. High external quantum efficiency of 65% for 1310 nm and 74% for 1550 nm, and a high 3-dB-down bandwidth of 41 GHz were demonstrated. No significant degradation of the frequency response was observed up to an average photocurrent of 10 mA. Moreover, a clear receiving eye-waveform was obtained at 40 Gb/s for an implemented single-output receiver module.
Two types of waveguide photodiodes (WG-PD) - an evanescently coupled photodiode (EC-WG-PD) and a separated-absorption-and-multiplication avalanche photodiode (SAM-WG-APD) - have been developed for use in 40-Gbps receivers. The EC-PD is much more robust than a conventional WG-PD under high optical input operation because of its distributed absorbed optical power density along the light propagation in the waveguide. The EC-WG-PD simultaneously exhibited a high external responsivity of 0.96 A/W, a wide bandwidth of >40 GHz, and as high as 10-mA photocurrent operation. On the other hand, the SAM-WG-APD has a wide bandwidth of 30-35 GHz and a gain-bandwidth product of 140-180 GHz as a result of its small waveguide mesa structure and a thin multiplication layer. Record highest receiver sensitivities of -28.8 dBm at 10 Gbps and -19.6 dBm at 40 Gbps have been achieved for the first time.
A separated-absorption-and-multiplication (SAM) AlInAs/GaInAs waveguide avalanche photodiode (APD) has been developed for 40-Gbps receivers. It has the widest bandwidth of 30-35 GHz and a gain-bandwidth product of 140-180 GHz, as a result of its small waveguide mesa structure and a thin 0.1micrometers thick avalanche layer. Preliminary results show the highest 10-Gbps sensitivity ever reported: -28.8 dBm at a bit-error-rate of 10-9. This waveguide APD is a candidate for 40-Gbps applications as a cost-effective super-efficient photodetector.
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