Duan and his co-workers developed their photodetector — known as an avalanche photodiode — using one of the fastest photodetector designs available. The device is made from semiconductors that operate under an applied electrical field at high voltage. In this field, arriving light excites electrons. They gain so much energy that it leads to an ‘avalanche’ of electrons, which can be easily detected. Since silicon is not suitable for infrared light detection, the related element germanium is typically used instead.
An electron microscope image of the avalanche photodetector developed at A*STAR. The device measures 30 micrometers in diameter.
© 2012 A*STAR Institute of Microelectronics
Optics Express - 310 GHz gain-bandwidth product Ge/Si avalanche photodetector for 1550 nm light detection
The detectors fabricated from these structures (see image) are designed for operation at wavelengths of around 1,550 nanometers, which is the spectral region used in telecommunications. Compared to a normal germanium photodetector, the avalanche design has enhanced the detected signal by a factor of 30. The gain-bandwidth product, which characterizes both the detector enhancement as well as operation speed, is as high as 310 gigahertz. This level is twice that of the traditional avalanche photodetectors based on compound semiconductors such as gallium–arsenide.
Further research is needed so that these detectors can be integrated with other electronic components on the same chip. A transimpedance amplifier, which converts electrical current from the photodetector into an electrical voltage, is an important component still lacking on the chips.
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