Dark current improvement due to dry-etch process in InAs/GaSb type-II superlattice LWIR photodetector with nBn structure

Abstract

The dark current of long wavelength infrared (LWIR) detector should be reduced to improve performance and decrease the system size, weight and power consumption (SWaP). In this work, we present the process to reduce the dark current of T2SL LWIR detector with nBn structure. The nBn structure consists of InAs/GaSb 14/7 monolayers (MLs) contact layer and absorber separated by Al0.2Ga0.8Sb barrier. For T2SL LWIR detector, the barrier structure is often used to reduce the dark current and passivate absorber. However, the barrier itself is very fragile and easily damaged during the device process. The proposed process was developed so that Al0.2Ga0.8Sb barrier is not damaged by any solution from the isolation etch process to the passivation process. In this process, CHF3 plasma treatment after the isolation etch with ICP reduced significantly the dark current. We attribute this to damage reduction of Al0.2Ga0.8Sb barrier by CHF3 plasma treatment. The 15 μm pitch devices fabricated with optimal process conditions showed the dark current density of less than 2.0 × 10−5 A/cm2 at −0.3 V and 80 K.