Far infrared Ga1-xInxSb/InAs-based strained-layer superlattice detectors grown by OMVPE

Strained-layer, type-II Ga_1-xIn_xSb/InAs superlattice detectors operating at 9 μm have been grown for the first time by OMVPE. In all reported literature thus far, MBE has been exclusively used to grow this particular material system. In the present research, the material was grown by an atmospheric pressure OMVPE reactor using high purity metallorganic precursors (TM Ga, TMSb, TMIn and TBAs). A 300 Å of Ga_1-xIn_xSb buffer layer was grown on n-GaAs(100) substrate followed by 20 periods (60 Å Ga_0.6In_0.4Sb/60 Å InAs) superlattice. A 300 Å InAs was grown as the capping layer. The growth took place at 600°C with a precracker temperature of 140°C. The absorbance characteristics measured by FTIR showed a shift in the cutoff wavelength λ from 1.8 μm to 2.5 μm when the In mole fraction was varied from 0.1 to 0.4 in Ga_1-xIn _xSb layer. The use of InAs in Ga_0.6In_0.4Sb/InAs structures introduces strain and λ shifts from 2.5 μm to 9 μm as confirmed by FTIR. An increase in the number of superlattice periods (from 5 to 20) resulted in an enhanced absorbance edge. p-n photodiodes were fabricated by establishing AuGe/Ni/AuGe contacts on InAs and n-GaAs. The samples were sintered at 430°C for 10 minutes in N₂ ambient. The samples were measured to show good I-V and R-V characteristics. The detector was edge-excited using white light to show change in conductance. The measured leakage current (1 mA<at a bias of -0.2 V) and was attributed to the lattice mismatch between GaAs and Ga_0.6 In_0.4Sb (~8%). A reduction in leakage current (or, improved electrical characteristics) is currently under investigation using a GaSb substrate