Investigation of surface leakage current in MWIR HgCdTe and InAsSb barrier detectors

In this paper we have investigated dark current sources in high-operating temperature HgCdTe and InAsSb and barrier infrared detectors fabricated using metal organic chemical vapour deposition and molecular beam epitaxy, respectively. The bulk leakage and surface leakage components of the dark current were determined for unpassivated devices fabricated in a round mesa geometry and in different sizes, from 100 to 500 μm diameters. Results show that the surface leakage current depends on both the conductivity types of the active layers and the semiconductor surfaces. In the InAsSb detector the bulk component constitutes 100% of the total dark current flowing through the heterostructure. Since the absorber region has the same conductivity type in its bulk and at its surface, the unipolar barrier blocks the current in the bulk, and also blocks the current along the n-type surface of the device. For the HgCdTe detector, the bulk component constitutes about 50% of the total dark current density in the 200 μm device operating at 230 K and −0.1 V, whereas for the InAsSb detector this share is much higher and amounts to 98%. In the HgCdTe detector, the surface leakage current is attributed to the sidewall surfaces along the absorber, as well as depleted surface. In InAsSb, the surface states are pinned into the conduction band, thus the surface current is limited and comes mainly from the depleted area.