Abstract
In this thesis, we have investigated the fundamental property of the InGaAs–capped quantum dot infrared photodetectors (QDIPs) and their applications in broadband detection and thermal imaging. Compared with standard InAs/GaAs QDIPs, InGaAs–capped QDIPs have the detection wavelength which is shifted from 6 to 7.9 μm. The results suggest that the dominant transition mechanism in the InGaAs–capped QDIPs is from the QD excited state to the InGaAs QW ground state, which reduced energy difference between the two states. By decreasing the InAs QD coverage from 2.5 to 2.0 ML, an even longer detection wavelength 10.4 μm is observed. Due to the QD excited state is pushed closer to the QW ground state in the InGaAs capping layer. With the device performance of standard and InGaAs–capped QDIPs, a straightforward approach to achieve broadband QDIPs is to stack the two structures into one device. The device would exhibit a wide detection window ranging from 4 to 11 μm with high responsivities. The phenomenon is attributed to the high responsivities of the standard QD and the InGaAs–capped QD structures in the MWIR and LWIR ranges, respectively. We bring up a simple ideal that without the complicated fabrication process, precise focusing mirror lens and readout integrated circuit (ROIC) prepare for focal plane array to extract the large–format, the thermal imaging formation can be obtained easily by a single–device scanning. It is a promising step for diagnosing diseases from a tiny cell.