Optimization of HgCdTe nBn photodetectors utilizing a superlattice barrier

Abstract

HgCdTe is an excellent material for mid-wavelength infrared photodetectors, but it can be costly when grown on nearly lattice-matched CdZnTe substrates. Growth on lower cost, lattice-mismatched CdTe/Si introduces defects in the material, reducing performance in conventional detector structures. This work examines a possible solution to this, namely, devices grown on CdTe/Si substrates by molecular beam epitaxy using the nBn device architecture, outlining the design concerns and the impacts of replacing the barrier with a type III superlattice. nBn devices were fabricated with an alloy barrier and others with a superlattice barrier, with both designs showing higher than expected dark currents. The cause of the high dark currents was determined to be an insufficient barrier in the conduction band. The superlattice design was further investigated using k⋅p modeling and device simulations, showing little benefit to the valence-band offset from modifying the band alignment, but significant improvement to the dark current from the increased electron effective mass in the barrier.