Electrical and optical characterisation of InGaAsSb-based photodetectors for SWIR applications

Abstract

The In(x)Ga(1−x)As(y)Sb(1−y) alloy was studied in epilayers and photodiodes grown lattice matched to GaSb across a comprehensive composition range, 0 ≤ x ≤ 0.3, as a promising technology to support the extended short-wave infrared region ∼ 1.7−3 μm. Low background carrier concentrations between 6 × 10^14 and 1 × 10^15 cm−3 were achieved in all samples, reducing with In fraction. Both the absorption coefficient and external quantum efficiency were found to increase with indium fraction, up to ∼ 10^4 cm−1 and 70% without an AR coating, respectively. Counter to the fundamental bandgap dependence, leakage current density initially reduced with the addition of low In and As fractions, before rising as the fractions increased and the bandgap reduced further. These properties resulted in specific detectivity reaching a maximum in the sample with x = 0.043, before decreasing towards higher alloy fractions. It is concluded that for moderate In fractions, the InGaAsSb alloy offers clear potential to improve on the disappointing material and photodiode properties of GaSb and support emerging SWIR sensing applications. However, development of fabrication and passivation technology is required to fully exploit this potential.