HMSM Photodetectors for High-Speed Applications

In this paper we describe the characterization of a family of optical devices based on heterojunction and heterodimensional structures and we investigate their static and dynamic properties. Such devices are good candidates, due to their high performance, for utilization as the sensing element for the realization of sensors in the fields of telecommunications, remote sensing, LIDAR and medical imaging. First, we present a Heterostructure Metal- Semiconductor-Metal (HMSM) photodetectors that employ a uniformly doped GaAs/AlGaAs heterojunction for the dual purpose of barrier height enhancement and creating an internal electric field that aids in the transport and collection of the photogenerated electrons. In this first family of devices, two doping levels are compared showing the direct effect of the aiding field due to modulation doping. Subsequently, we analyse a novel Resonant-Cavity- Enhanced (RCE) HMSM photodetector in which a Distributed Bragg Reflector (DBR) is employed in order to reduce the thickness of the absorption layer thus achieving good responsivity and high speed as well as wavelength selectivity. Current-voltage, photocurrent spectra and highspeed time response measurements point out the better performance of this last family of detectors, as they can operate in tens of Giga-Hertz range with low dark current and high responsivity. Particularly, the I-V curves show a very low dark current (around 10 picoamps at operative biases) and the photocurrent spectrum shows a clear peak at 850 nm wavelength. Combination of very low dark current wavelength selectivity, and compatibility with high electron mobility transistors makes these devices especially suitable for the above-mentioned applications.