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Researches On Physics Of Long/Very Long Wavelength Infrared Quantum Cascade Detectors

Posted on:2018-02-03Degree:DoctorType:Dissertation
Country:ChinaCandidate:L LiFull Text:PDF
GTID:1318330512494254Subject:Microelectronics and Solid State Electronics
Abstract/Summary:PDF Full Text Request
As an optimization and an alternative choice of quantum well infrared photodetectors,quantum cascade detectors were proposed and investigated from the beginning of 21st century.The advantages of quantum cascade detectors include high uniformity,matured process,high operability,photovoltaic,no dark current,high working temperature and high speed.However,the inter-subband transition mechanism leads to the non-absorption of the normal incident photons and the low quantum efficiency.At the same time,infrared imaging technology has been developed into the 3rd generation with multi-color,large scale and small pixels focal plane arrays,and the staring imaging with high resolution,high accuracy and high sensitivity of objects can be obtained.Therefore,the performances of quantum cascade detectors are expected to be optimized.The performances of photodetectors can be optimized in optics and electronics.In optics,the optical coupling efficiency is expected to be improved.And in electronics,both a higher intrinsic responsivity and a lower device noise are expected.The focus of our work is surrounded by the optimization in optical coupling,intrinsic responsivity and noise of quantum cascade detectors.The main works consists:1.In optics,plasmonic micro-cavity quantum cascade detector is fabricated.The peak responsivity can be enhanced from 42 mA/W to 176 mA/W with 4.1 times enhancement.And blackbody responsivity can be enhanced from 2.73 mA/W to 8.2 mA/W with 3 times enhancement.This detector presents an excellent polarization discrimination performance with extinction ratio of 127.Based on this structure,a mid-long wavelength infrared two-color quantum cascade detector is proposed,whose detection wavelengths are 4.4 ?m and 9.0 ?m,respectively.In addition,a quasi-one-dimensional grating plasmonic micro-cavity is designed and investigated,which can satisfy surface plasmonic polariton and localized surface plasmon resonance conditions at the same time,which can further enhance the optical coupling efficiency.2.In electronics,a)To broaden the spectral linewidth of quantum cascade detectors,photoelectronic absorption of quantum cascade detectors is optimized.Broadband quantum cascade detectors are demonstrated in optimization of absorption region and barriers hight.With a pair of coupled quantum wells act as the absorption region,the relative spectral linewidth is broadened from 9.6%to 30.7%,which is the widest across all the reports of quantum cascade detectors and the shape of spectrum is insensitive to temperature.But shape of spectrum is sensitive to bias voltage,which can be applied in spectrum reconstruction and have significance in hyperspectral imaging.b)To achieve high transport efficiency,transport region of quantum cascade detectors is optimized.Combined energy mini-steps and phonon ladder,the peak responsivity of a very long wavelength infrared quantum cascade detector at zero bias condition is improved from 16 mA/W to 73 mA/W with 4.5 times improvement,which is the highest across all the reports of quantum cascade detectors at very long wavelength infrared band.In addition,the peak wavelength of GaAs/AlGaAs materials based quantum cascade detector is extended to 16.3 ?m.It confirms that quantum cascade detectors based on this material system have huge potential in very long wavelength infrared detection.c)To suppress device noise,investigations and optimizations on thermal noise and spectral noise are performed.Firstly,we present a joint experimental and theoretical investigation on a long wavelength infrared quantum cascade detector to reveal its dark current path.With assistance of magnetic field,magneto-phonon resonance is observed.Redundant quantum wells in transport region are expected to suppress dark current,increase device resistance and finally reduce device noise.In addition,by applying new material of contacts and changing alloying condition in process,the thermal noise is suppressed by one order of magnitude.Moreover,photoresponse of quantum cascade detectors is investigated to reveal the mechanism of multi-band response performance.Spectral noise can be classified into two groups which are ground-state based and non-ground-state based.The specific optimization design is proposed.
Keywords/Search Tags:Quantum cascade detectors, Infrared detection, Quantum well, Plasmonic micro-cavity
PDF Full Text Request
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