Electrical modulation of the LWIR absorption and refractive index in InAsSb-based strained layer superlattice heterostructures

Abstract

InAsSb-based strained layer superlattices (SLS) have strong fundamental absorption, which can be easily modified in a controlled manner by injecting excess carriers. This makes them attractive for intensity modulation of infrared lasers as well as beam steering and spatial beam shaping with a nanosecond-scale time response. This paper reports the modulation of the fundamental absorption and the refractive index by carrier injection in a 3.45-nm-period InAsSb0.65/InAsSb0.35 SLS with a low temperature energy gap of 85 meV grown by molecular beam epitaxy on a GaSb substrate with a GaInSb metamorphic buffer. The SLS absorber was sandwiched by n- and p-type wider energy gap layers for electrical injection and confinement of excess carriers. The population of conduction band states was obtained by measuring the intensity modulation of a 10.6 μm CO2 laser for temperatures ranging from T = 77 to 200 K. An increase of the electron quasi-Fermi level with electrical injection up to 20 meV was observed. The experimental data imply a decrease in the Auger coefficient with temperature, from 3 × 1024 cm6/s at 77 K to 1 × 1024 cm6/s at T = 200 K attributed to recombination involving two electrons and a heavy hole. The refractive index changes obtained by electrical injection of excess carriers can reach 0.05 at T = 77 K and 0.035 at T = 200 K, which are at least three orders of magnitude greater than those obtained with electro-optical materials.