InP/InAs quantum well infrared photodetectors

Güngör, Oğuz Onur
Quantum well infrared photodetectors (QWIPs) are advantageous regarding detector uniformity, stability, and cost compared to other infrared detector technologies. On the other hand, they suffer from low quantum efficiency (QE) because they cannot detect normal-incidence radiation. Diffraction-gratings and special mesa structures are used to increase QE by manipulating the incoming radiation. These solutions complicate the detector production process and increase the crosstalk between pixels. Also, they lose their effectiveness when the pixel size is reduced to have a higher resolution and lower cost. Recent studies on new material systems to increase QE give promising results even without diffraction-gratings and special mesa structures. This thesis presents grating-free mid-wavelength QWIPs with high conversion efficiency (CE) based on the InP/InAs material system on InP substrate. Molecular beam epitaxy grown epilayer of the detectors consisted of InP barriers and Si-doped InAs quantum wells. A diffraction-grating-free focal plane array (FPA) with 15 μm pitch and 640x512 format and individual pixel arrays were fabricated and characterized. The cut-off and peak responsivity wavelengths of the pixels were 6.2 and 5.5 μm, respectively. Responsivity measurements exhibited a peak responsivity as high as 2.7 A/W under -4.0 V bias voltage, corresponding to a peak CE of 61%. The mean noise equivalent temperature difference (NETD) of the FPA was approximately 28 mK with f/1.67 optics at 10 ms integration time, which is consistent with the calculated NETD based on the measurements on pixel arrays. These results show that QWIPs based on properly chosen alternative material systems are indispensable alternatives to HgCdTe and Type-II superlattice detectors.
Citation Formats
O. O. Güngör, “InP/InAs quantum well infrared photodetectors,” M.S. - Master of Science, Middle East Technical University, 2023.