Near-infrared InAs/GaSb Type-Ⅱ superlattices is widely used in biomimetics, sensing, color-imaging technology and other applications. An antireflection coating(AR coating) can help it perform better, making the infrared photodetector a higher responstivity and also a higher quantum efficiency. We produce a broadband AR coating by plasma-enhanced chemical vapor deposition(PECVD) then using the lift-off technology making no damage without any change in the usual Infrared detector process flow, a 260 nm SiO<sub>2</sub> AR coating is transform onto the surface of the infrared photodetector. After using the AR coating, the antireflection can provide up to 40% light gain, while the average reflectivity of the surface of InAs/GaSb type-Ⅱ superlattice is decreased from 33% to 14%. The responsitivity is increased obviously.
We report three kinds of surface passivation for AlxInyAsSb APD, which are SiO<sub>2</sub>, SiO<sub>2</sub> after sulfuration and SU8 2005 treatments. A good sidewall profile of mesas were etch by Inductively Coupled Plasma (ICP) to 2.6μm depth. The order of dark current for device with SU8 passivation is less than -12 under the temperature of 100K. Dark current and photocurrent increase linearly with diameter of mesa. Also, the devices with different passivation methods produce photocurrent excited by incident power. The measurements are consistent with CV modeling and electric field simulations.