Ga-free InAs/InAsSb T2SL XBn detector is now a reliable candidate for high-performance focal plane arrays in the MWIR (3-5μm) domain. However, this T2SL is a very anisotropic quantum structure having a type-IIb band offset alignment where electrons are rather delocalized all over the structure while holes are strongly confined in deep InAsSb quantum well. This configuration could penalize the absorption and the hole minority carrier transport but MWIR detector device without anti reflection coating shows quantum efficiency higher than 50%. Considering results of specific measurements and band structure calculation, possible carrier transport scenario is presented to explain such performance.
Monolithic integration of InAs/InAsSb type-II superlattice (T2SL) photodetector on large-scale Si wafers would allow the development of a low-cost, high-quality, Si-readout integrated circuit compatibility focal plane array (FPA). In this study, we compare the performances of MWIR InAs/InAsSb T2SL samples grown on Si and GaSb substrates. The material quality is investigated with High-Resolution X-ray Diffraction, Atomic Force Microscopy, and Photoluminescence (PL). A minority carrier lifetime of 800 ns at 150 K is extracted from time-resolved PL on the sample grown on GaSb/Si templates with dislocation filtering layers. The device performances will be reported at the conference.
In this communication, we report on electrical and electro-optical characterizations of InAs/InAsSb Type-II superlattice (T2SL) MWIR photodetector, showing a cut-off wavelength at 5 μm. The device, made of a barrier structure in XBn configuration, was grown by molecular beam epitaxy (MBE) on GaSb substrate. At 150K, dark current measurements shows a device in the Shockley-Read-Hall (SRH) regime but with an absolute value comparable to the state-of-the-art. A quantum efficiency of 50% at the wavelength of 3 μm for a 3 μm thick absorption layer is found in simple pass configuration and front-side illumination. Combined with lifetime measurements performed on dedicated samples through time resolved photoluminescence (TRPL) technique, mobility is extracted from these measurements by using a theoretical calculation of the quantum efficiency thanks to Hovel’s equations. Such an approach helps us to better understand the hole minority carrier transport in Ga-free T2SL MWIR XBn detector and therefore to improve its performance.
In this paper, we study the influence of three different etching depths on electrical and electro-optical properties of nonpassivated T2SL nBn Ga-free pixel detector having a 5μm cut-off wavelength at 150 K. The study shows the strong influence of lateral diffusion length on the shallow etched pixel properties and therefore, the need to perform etching through the absorber layer to avoid lateral diffusion contribution. The lowest dark current density was recorded for a deep-etched detector, on the order of 1 × 10-5 A/cm2 at 150 K and operating bias equal to – 300 mV. The quantum efficiency of this deep-etched detector is measured close to 55 % at 150 K, without anti-reflection coating. A comparison between electro-optical performances obtained on the three etching depths demonstrates that the etching only through the middle of the absorber layer (Mid-etched) allows eliminating lateral diffusion contribution while preserving a good uniformity between the diode’s performance. Such result is suitable for the fabrication of IR focal plane arrays (FPA).
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