Electrical Modulation Of The Lwir Absorption And Refractive Index In Inassb-Based Strained Layer Superlattice Heterostructures

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 85meV 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 mu m CO2 laser for temperatures ranging from T=77 to 200K. An increase of the electron quasi-Fermi level with electrical injection up to 20meV was observed. The experimental data imply a decrease in the Auger coefficient with temperature, from 3x10(24)cm(6)/s at 77K to 1x10(24)cm(6)/s at T=200K 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=77K and 0.035 at T=200K, which are at least three orders of magnitude greater than those obtained with electro-optical materials.