Novel heterostructure MSM photodetectors for gigabit ethernet

A key element in the field of sensors for short haul communications is the development of high performance photodetectors. Along this direction, we present here an accurate investigation of photodetectors based on AlCaAs/CaAs heterojunction structures. In these devices the absorption region is in the GaAs layer where is formed, at the interface with AlGaAs, a two-dimensional electron gas (2-DEC). This HMSM (Heterostructure Metal-Semiconductor-Metal) photodetector contains an AlGaAs distributed Bragg reflector for detection at 850nm. The beneficial effect of the two dimensional electron gas (2-DEG) in the GaAs absorption laver is evidenced by comparing samples with and without doping in the AlGaAs layer. We start from properties of the grown structure, and then we investigate the static and dynamic properties. Particularly, photocurrent spectra exhibit a 30nm wide peak at 850nm, while time response measurements give a bandwidth over 30GHz. Combination of very low dark current and capacitance, fast response, wavelength selectivity, and compatibility with high electron mobility transistors makes this device especially suitable for Gigabit Ethernet applications.