Quantum dot infrared photodetectors under the influence of proton irradiation

Quantum dot infrared photodetectors (QDIP) have shown promising performance in various applications such as surveillance, night vision and applications in space. QDIPs have many advantages compared to their counterpart quantum well infrared photodetectors (QWIP). The advantages of the QDIP include: (1) sensitive to normal-incidence light which simplifies the configurations for imaging systems, (2) longer lifetime of carriers because of the decreased electron-phonon scattering which lead to a high photoconductive gain (3) lower dark current because of the three dimensional confinement of the carriers which enable higher operating temperature. Recent studies have shown that the QD structures and QD-based devices are much more resistant to irradiation than bulk semiconductors or quantum wells, which make QDIPs a promising candidate for space applications.;The objective of this work is to design and fabricate quantum dot infrared photodetectors and investigate the influence of the proton irradiation on the fabricated photodetectors. The photodetectors in this work were grown by using molecular beam epitaxy (MBE) technique. The final devices were fabricated by standard processing techniques including photolithography, chemical wet etching, evaporative metal deposition, lift-off and rapid thermal annealing. The dark current of the photodetectors was measured at temperatures of 77K. The photoresponse ranging from visible and near infrared (NIR) band to middle infrared (MIR) band was observed under different temperatures and bias voltages. Then, the photoresponse and I-V characteristics of the devices were investigated as a function of proton fluences in the range of 9.0x1010 -- 5.0x1014 cm-2. The intensity of the photoresponse spectra was reduced by about two orders of magnitude after irradiating the device with a fluence of 5.0x1014 cm -2. On the other hand a partial recovery of the photoresponse is observed when the rapid thermal annealings were done on the device.