Paving the Way to Infrared Beam Steering with CMOS Circuits
Paper title: Electrical modulation of the LWIR absorption and refractive index in InAsSb-based strained layer superlattice heterostructures
- Jinghe Liu (student), Dmitry Donetsky, Haying Jiang (student), Gela Kipshidze, Leon Shterengas, Gregory Belenky, Dept. of ECE, Stony Brook University, Stony Brook, NY 11794
- Wendy L. Sarney and Stefan P. Svensson, CCDC US Army Research Laboratory, 2800 Powder Mill Rd, Adelphi, MD 20783.
J. Appl. Phys. 128, 083101 (2020); Editor’s Pick https://doi.org/10.1063/5.0016149
Novel Technical Contribution
The modulation of refractive index by up to 0.05 with electrical carrier injection was demonstrated in InAsSb-based semiconductor compounds with engineered energy gaps. This change is three orders of magnitude greater than what is achievable in conventional electro-optical materials employed in long-wave infrared wavelength range.
Commercially-available electro-optical modulators for free-space longwave infrared laser sources have the bandwidth limited by capacitive cell impedance and require high voltage drivers. The proposed approach enables the device operation with a nanosecond-scale time response with CMOS-compatible voltage and current levels. Low power requirements make it possible to develop arrays of integrated devices for optical beam steering and shaping.
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 InAsSb 0.65/InAsSb 0.35 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 CO 2 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 × 10 24 cm 6/s at 77 K to 1 × 10 24 cm 6/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.