GaInAsSb absorbers and AlGaAsSb multipliers for 2- <b> <i>μ</i> </b> m separate absorption charge and multiplication avalanche photodiodes

Abstract

Ga0.71In0.29As0.25Sb0.75 and Al0.85Ga0.15As0.07Sb0.93 layers were grown on GaSb (100) substrates and characterized as candidate absorber and multiplier materials for 2 μm separate absorption, charge, and multiplication (SACM) avalanche photodiodes (APDs). The Ga0.71In0.29As0.25Sb0.75 p–i–n structures exhibited smooth surface morphology with a root mean square (RMS) roughness of 1.43 Å and photoluminescence centered at 2.37 μm. Capacitance–voltage analysis determined that the unintentionally doped absorber is n-type with a background concentration of 3.5 ± 0.5 × 1015 cm−3. Dark current measurements across varying mesa diameters showed a clear perimeter dependence, indicating dominant surface leakage. The Al0.85Ga0.15As0.07Sb0.93 n–i–p multipliers demonstrated good crystalline quality with RMS surface roughness below 2 Å. Capacitance–voltage measurements identified p-type behavior with a background doping of 2.5 ± 0.5 × 1016 cm−3. Variable-area diode analysis showed that 96%–99% of the total dark current originates from surface leakage. These results provide baseline electrical and structural parameters for future GaSb-lattice SACM APD design and highlight the need for improved control of background doping and surface passivation.