T2SL Mid- and Long-Wave Infrared Photodetector Structures Grown on (211)B and (311)A GaSb Substrates

We recently evaluated the optical and electric characteristics of mid-wave photodetector (PD) diodes grown on high-index substrates(1). Preliminary results indicate that substrate orientation and surface polarity can modify PD parameters such as photoluminescence (PL), dark current (Jd), quantum efficiency, and spectral characteristics. In this work, we focused on growth parameter optimization for long-wave type-II strained layer superlattice (T2SL) PD structures grown on (211) B and (311) A GaSb substrates. Material and PD diode characteristics were compared with reference data obtained on (100)-oriented substrates. Material quality was evaluated by HRXRD, AFM, Nomarski microscopy, 77 K PL, and PD J-V and spectral testing. Photoluminescence and cutoff wavelength measurements for diode structures fabricated on (211) B and (311) A substrates demonstrate a significant redshift due to a reduction of the optical bandgap in the SL. The extent of redshift increases with superlattice period and Sb mole fraction in the InAsSb layers in the absorber. All wafers demonstrated reasonable surface morphology without surface corrugation, with minor variability in roughness. Redshift in 77 K PL and cutoff wavelength, in combination with high QE and low Jd, obtained from growths on these high-index substrates offer a potential path to achieve enhanced PD characteristics with reduced SL period for a given wavelength by comparison to (100) substrates.