Structural Design Of Long Wavelength Interband Cascade Photodetector

Since the invention of InAs/GaSb II superlattice Infrared detector,which has become a hot spot in the field of infrared detection because of its energy band structure is flexible and adjustable.By adjusting the thickness of InAs and GaSb layers,the detection wavelengths can be covered from 3?m to 30?m.In addition,the mature IIIV material growth technology also provides conditions for the growth of high performance infrared photodetectors.The interband cascade photodetector is a barrier type devices based on the InAs/GaSb II superlattice absorption region,which uses the phonon assistant relaxation,resonance tunneling and barrier resistance.The photogenerated carrier is produced in the superlattice absorption region.Because of the barrier,photogenerated carrier can only move in the single direction of the relaxation region,enters the tunneling zone quickly by the phonon assistant relaxation and then passes through the resonance tunnel to reach the valence band of the next stage superlattice absorption region.There is no purposely doped PN junction in the interband cascade photodetector,and the carrier transport is realized by barrier,which can effectively inhibit the generation-recombination current and tunneling current in the long wave detection.For the shorter carrier diffusion length than the medium wave detection in long wave detection,the interband cascade structure adopts a discrete multistage absorption region structure,and the thickness of the absorption region is less than the carrier diffusion length,which ensures the normal collection of optical carriers.Therefore,the interband cascade structure can be used to prepare high performance long wave infrared photodetectors.The aim of this research is to design and optimize the band structure of the long wavelength interband cascade photodetector,then to prepare and test the device.The main contents are as follows:1.The structure model and calculation of the multi quantum well band structure are studied.The two band model and the transfer matrix method under the envelop function approximation are used to calculate the relaxation region of the multi quantum well in the long wave interband cascade.The effect of substrate strain on the band position of the long wave interband cascaded material is further considered,and the calculation model of the phonon scattering rate is given,which lays a theoretical foundation for further optimizing the structure of the device.2.On the basis of the calculation model,the influence of the thickness of each layer on the ground state energy level and the difference of the ground state energy level of the adjacent potential well is studied.The energy band structure scheme of the long wave interband cascade detector is given.The periodic quantum well relaxation zone structure is proposed to expand the relaxation zone thickness,reduce the electric field intensity in the absorption area,and suppress the compound current and tunneling current on the premise of ensuring the tunneling probability of the optical carrier in the relaxation region.3.Through the MBE and other devices,the long wavelength interband cascade detector unit device was prepared,and the spectral response test,the blackbody response test and the dark current test were carried out.The 50% cut-off wavelength of the device 80 K is measured at 11.5 ?m,and the cut-off wavelength of 100% is over 13 ?m.The quantum efficiency of the device is 20% at 10.5 ?m.It is the longest wavelength infrared detector at present with the interband cascade structure at 80 K.The dark current test results were fitted and the composition of dark current at different temperatures was analyzed.