Photodetectors based on heterostructures for optoelectronic applications

In this work we describe 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 analyze 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, current-temperature, photocurrent spectra, high-speed time response, and on-wafer frequency domain 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); C-V measurements highlight the low geometrical capacitance values; the photocurrent spectrum shows a clear peak at 850 run wavelength, while time response measurements give a 3 dB bandwidth of about 30 GHz. Small signal model based on frequency domain data is also extracted in order to facilitate future photoreceiver design. Furthermore, two-dimensional numerical simulations have been carried out in order to predict the electrical properties of these detectors. Combination of very low dark current and capacitance, fast response, wavelength selectivity, and compatibility with high electron mobility transistors makes these devices especially suitable for the above-mentioned applications.