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- Creators: Vasileska, Dragica
Description
The long wavelength infrared region (LWIR) and mid wavelength infrared region (MWIR) are of great interest as detection in this region offers a wide range of real time applications. Optoelectronic devices operating in the LWIR and MWIR region offer potential applications such as; optical gas sensing, free-space optical communications, infrared counter-measures, biomedical and thermal imaging etc. HgCdTe is a prominent narrow bandgap material that operates in the LWIR region. The focus of this research work is to simulate and analyze the characteristics of a Hg1-xCdxTe photodetector. To achieve this, the tool `OPTODET' has been developed, where various device parameters can be varied and the resultant output can be analyzed. By the study of output characteristics in response to various changes in device parameters will allow users to understand the considerations that must be made in order to reach the optimum working point of an infrared detector. The tool which has been developed is a 1-D drift diffusion based simulator which solves the 1-D Poisson equation to determine potentials and utilizes the results of the 1-D electron and hole continuity equations to determine current. Parameters such as absorption co-efficient, quantum efficiency, dark current, noise, Transit time and detectivity can be simulated. All major recombination mechanisms such as SRH, Radiative and Auger recombination have been considered. Effects of band to band tunnelling have also been considered to correctly model the dark current characteristics.
ContributorsMuralidharan, Pradyumna (Author) / Vasileska, Dragica (Thesis advisor) / Wijewarnasuriya, Priyalal S. (Committee member) / Zhang, Yong-Hang (Committee member) / Arizona State University (Publisher)
Created2011
Description
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.
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.
ContributorsHe, Zhaoyu (Author) / Zhang, Yong-Hang (Thesis advisor) / Vasileska, Dragica (Committee member) / Goryll, Michael (Committee member) / Johnson, Shane (Committee member) / Arizona State University (Publisher)
Created2016