Detecting Infrared Radiation Beyond the Bandoffset With Intersubband Transitions

InGaAs/InAlAs quantum well (QW) infrared photodetector structures have been investigated to reach operation energies larger than the heterostructure bandoffset. The structures are composed of superlattices having a central QW with a thickness different from the others, behaving as a defect within the periodic structure. The central QW gives rise to localized states in the continuum, allowing absorption and current generation for the radiation of energies beyond the bandoffset. The detection of radiation as large as 587 meV (2.11 μm) has been achieved with intrinsic intersubband transition from the ground state to the second localized excited state in the continuum, as manifested by absorption and photocurrent measurements. Theoretical calculations fully agree with the experimental data, strongly supporting the analysis of the results.