Abstract
Microjunction InAs/InAs1−xSbx type-II superlattice-based long-wavelength infrared photodetectors with reduced dark current density were demonstrated. A double electron barrier design was employed to reduce both bulk and surface dark currents. The photodetectors exhibited low surface leakage after passivation with SiO2, allowing the use of very small size features without degradation of the dark current. Fabricating microjunction photodetectors (25 × 25 µm2 diodes with 10 × 10 µm2 microjunctions) in combination with the double electron barrier design results in a dark current density of 6.3 × 10−6 A/cm2 at 77 K. The device has an 8 µm cut-off wavelength at 77 K and exhibits a quantum efficiency of 31% for a 2 µm-thick absorption region, which results in a specific detectivity value of 1.2 × 1012 cm·Hz1/2/W.
Highlights
After InAs/Ga(In)Sb type-II superlattices (T2SLs) were devised by Sai-Halasz et al.[1] and used by Sakaki et al to make infrared photodetectors, they have been optimized[3,4] and have started to challenge mercury cadmium telluride (MCT), which is the state-of-the-art infrared detection technology
Where A is the electrical area of the photodetector, W(V) is the depletion region width under a given applied bias voltage (V), ni is the intrinsic carrier concentration, τ0 is the carrier lifetime, Eg is the bandgap energy of the depletion region, and Nc and Nv are the density of states in the conduction and valence bands, respectively
The CpDBn structure was grown with a solid-source molecular beam epitaxy (SSMBE) system on an n-type Te-doped GaSb wafer
Summary
After InAs/Ga(In)Sb type-II superlattices (T2SLs) were devised by Sai-Halasz et al.[1] and used by Sakaki et al (ref.2) to make infrared photodetectors, they have been optimized[3,4] and have started to challenge mercury cadmium telluride (MCT), which is the state-of-the-art infrared detection technology. The valence and conduction energy bands can be separately engineered thanks to the flexibility of superlattice structures This is done by changing the thicknesses of InAs and Ga(In)Sb layers. Dark current reduction in T2SL photodetectors is one of the main challenges to increase the specific detectivity (D*), which is the main figure of merit for photodetectors that combines both optical and electrical performance. These photodetectors still suffer from higher dark current density compare to their MCT-based counterparts. One example of this concept is the nBn device structure, which is able to reduce the G-R current by pushing the depletion region into a large-bandgap electron barrier area[22]
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