The work contained in this thesis is concerned with the performance of infrared integrating detector arrays, within the context of astronomical spectroscopy. A linear array of thirty-two InSb photo diodes is investigated. It is found to exhibit good capacitance and dark current uniformity across the array. By applying the principle of charge conservation to the multiplexed readout arrangement of this device, the signal response of the detector to different levels of illumination is derived. It is found from this, and confirmed experimentally, that the device has a highly linear radiation response over a range of reverse biases. The interaction between dark current and photo-current is studied,primarily by the application of a simple model. The results indicate that the effective signal gain of a detector can vary in the situation where dark current dominates the discharge processes, since in this instance accurate dark current subtraction becomes difficult. The predictions of the model are compared with experiments performed on two integrating arrays; one under study in the laboratory,and the other installed in the low background environment of a cooled grating spectrometer. Finally, suggestions are presented of ways of avoiding this problem, the simplest of which involves utilizing, where possible, low dark current detector materials. The importance of achieving good dark current uniformity with arrays is stressed, since this will improve the ability to flat-field faint object spectra. To illustrate the importance of these devices, infrared spectra obtained with array detectors, covering a range of astronomical objects,are presented and discussed.

abstract: This work demonstrates novel nBn photodetectors including mid-wave infrared (MWIR) nBn photodetectors based on InAs/InAsSb type-II superlattices (T2SLs) with charge as the output signal, and visible nBn photodetectors based on CdTe with current output. Furthermore, visible/MWIR two-color photodetectors (2CPDs) are fabricated through monolithic integration of the CdTe nBn photodetector and an InSb photodiode. The MWIR nBn photodetectors have a potential well for holes present in the barrier layer. At low voltages of < −0.2 V, which ensure low dark current <10-5 A/cm2 at 77 K, photogenerated holes are collected in this well with a storage lifetime of 40 s. This charge collection process is an in-device signal integration process that reduces the random noise significantly. Since the stored holes can be readout laterally as in charge-coupled devices, it is therefore possible to make charge-output nBn with much lower noise than conventional current-output nBn photodetectors. The visible nBn photodetectors have a CdTe absorber layer and a ZnTe barrier layer with an aligned valence band edge. By using a novel ITO/undoped-CdTe top contact design, it has achieved a high specific detectivity of 3×1013 cm-Hz1/2/W at room temperature. Particularly, this CdTe nBn photodetector grown on InSb substrates enables the monolithic integration of CdTe and InSb photodetectors, and provides a platform to study in-depth device physics of nBn photodetectors at room temperature. Furthermore, the visible/MWIR 2CPD has been developed by the monolithic integration of the CdTe nBn and an InSb photodiode through an n-CdTe/p-InSb tunnel junction. At 77 K, the photoresponse of the 2CPD can be switched between a 1-5.5 μm MWIR band and a 350-780 nm visible band by illuminating the device with an external light source or not, and applying with proper voltages. Under optimum conditions, the 2CPD has achieved a MWIR peak responsivity of 0.75 A/W with a band rejection ratio (BRR) of 52 dB, and a visible peak responsivity of 0.3 A/W with a BRR of 18 dB. This 2CPD has enabled future compact image sensors with high fill-factor and responsivity switchable between visible and MWIR colors. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016