Mushroom-Mesa Photodetectors Using Subwavelength Gratings as Focusing Reflectors

A novel grating-integrated mushroom-mesa photodetector is demonstrated, which uses an undercut mushroom-mesa structure and a grating focusing reflector to increase bandwidth and efficiency simultaneously. The mushroom-mesa p-i-n structure is heterogeneously integrated on a non-periodic concentric circular subwavelength grating by a wafer bonding process. High speed can be obtained by using a mushroom-mesa structure for reducing its RC time constant. Meanwhile, high quantum efficiency can be obtained by using a grating reflector for its focusing ability. The external quantum efficiency measured on a device of 30 μm in diameter is 45.28% at a wavelength of 1.55 μm, which is enhanced by 21.4% in contrast to the device without reflector. And a 3-dB bandwidth of 30 GHz at a reverse bias of 3 V is simultaneously measured for our photodetector.