Band gap tuning of InAs∕GaSb type-II superlattices for mid-infrared detection

Abstract

The superlattice (SL) of a 40 period InAs∕GaSbSL structure were varied around the 20.5ÅInAs∕24ÅGaSb design in order to produce a device with an optimum mid-infrared photoresponse and a sharpest photoresponse cutoff. The samples for this study were grown by molecular beam epitaxy with precisely calibrated growth rates. Varying individual layer width around the nominal design, we were able to systematically change the photoresponse cutoff wavelength between 4.36 to 3.45um by decreasing the InAs width from 23.5 to 17.5Å, and between 4.55 to 4.03μm by increasing the GaSb width from 18 to 27Å. Therefore, the cutoff changes faster with decreasing InAs rather than increasing GaSb width. However, increasing GaSb width more effectively enhances the sharpness of photoresponse near band edge. The effect of design parameters on the photoresponse cutoff and other effects are explained by a nonperturbative, modified envelope function approximation (EFA) calculation that includes the interface coupling of heavy, light, and spin-orbit holes resulting from the in-plane asymmetry at InAs∕GaSb interfaces. Using the modified EFA model, the SL design at fixed period of 44.5Å was adjusted for the optimum performance.

On the structural characterization of InAs/GaSb type-II superlattices: The effect of interfaces for fixed layer thicknesses

“…The in-plane lattice mismatch can be minimized by engineering the interfaces (between InAs and GaSb layers) which is known to have a profound effect on the device performance [10,[13][14][15][16]. Introducing special interface recipes during the growth of SLs to intentionally form 0 to 1 monolayer (ML) thick GaAs-and/or InSb-like interfaces are widely used by many research groups [8,13,14,[16][17][18][19][20][21][22]. Because of the differences in the lattice parameters, the structure can be either under compressive or tensile strain depending on the interfaces.…”

“…It is possible to tune the effective bandgap over a wide range of detection regions (3-30 μm) by changing the InAs and GaSb individual layer thicknesses in the SL [6][7][8][9][10][11]. Thanks to the development in the epitaxial growth techniques such as molecular beam epitaxy (MBE), it has been possible to grow numbers of successive high quality very thin layers of different materials.…”

MBE growth of mid-IR diode lasers based on InAs/GaSb/InSb short-period superlattice active zones

“…This system has been studied till now mainly to fabricate IR detectors operating at wavelength longer than 5 mm based on SLs with periods in the 20 monolayers (MLs) range [2]. Shorter wavelengths in principle can be achieved with shortperiod SLs (SPSLs) where the period is as thin as 5-10 MLs.…”

“…The ''type-II broken gap'', also called type-III, band alignment at the InAs-GaSb interface allows one to adjust the effective bandgap of InAs/GaSb superlattices (SLs) from the mid-to the long-IR range by adjusting the individual-layer thickness and SL period [2]. This system has been studied till now mainly to fabricate IR detectors operating at wavelength longer than 5 mm based on SLs with periods in the 20 monolayers (MLs) range [2].…”

Antimonide superlattice complementary barrier infrared detector (CBIRD)

“…The versatility of the antimonides has been manifested in a variety of semiconductor devices. The antimonides have also emerged recently as a highly effective platform for developing of sophisticated heterostructure-based mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) detectors, as exemplified by the high-performance double heterstructure (DH) [2], nBn [3][4][5], XBn [6][7][8][9], and type-II superlattice infrared detectors [10][11][12][13][14][15][16][17][18]. A key enabling design element is the unipolar barrier [18], which is used to implement the barrier infrared detector (BIRD) design for increasing the collection efficiency of photogenerated carriers, and reducing dark current generation without impeding photocurrent flow.…”