Effects of etching processes on surface dark current of long-wave infrared InAs/GaSb superlattice detectors
Surface leakage in long-wave infrared InAs/GaSb superlattice detectors is closely related to the state of Sb on the sidewall surface. The presence of free Sb on the sidewall surface after wet etching and GaSb after dry etching at 90 °C can considerably deteriorate the electrical performance of the detector. By using a Cl2/N2 inductively coupled plasma dry etching process at 170 °C, the formation of free Sb or GaSb on the sidewall surface of the sample was prevented, resulting in a low dark current density. The 640 × 512 focal plane array which mesa sidewalls were passivated with silicon nitride film had a cut-off wavelength of 12 μm. The dark current density measured on a single pixel was 1.3 × 10-5 A/cm2 at the bias of -0.05 V and the corresponding resistance-area product at zero resistance (R0A) was 830 Ω∙cm2. The mean peak detectivity (D*) was measured to be 6.6 × 1010 cm Hz1/2/W and the noise equivalent differential temperature as low as 17.2 mK at 60 K.