Long-wavelength Infrared Barrier Detectors Based On InAs/InAsSb Type-Ⅱ Superlattices

Type-Ⅱ superlattice materials are widely used in detectors,lasers and modulators,etc.,and have shown great potential especially for infrared detection.InAs/InAs_1-xSb_xsuperlattice materials can achieve band gap adjustment through energy band engineering,which is more flexible in device design,and the minority carrier lifetime is relatively longer,and the photodetectors have lower dark current density than ⅡI-V bulk detectors.In order to achieve the absorption of InAs/InAs_1-xSb_x materials for long-wave infrared,a superlattice with a long period is required,which can lead to a low absorption coefficient.Moreover,the hole effective mass restricts the carrier transport,resulting in a short diffusion length.Thus,compared with the state-of-the art ⅡI-V bulk detectors,the InAs/InAs_1-xSb_x based detectors are generally suffer from low quantum efficiency.To address the above issue,this study introduces a built-in electric field within the absorption region to enhance the carrier transport by using a stepped absorber design.The bandgap energies and electron affinities of each constitution absorbers can be tailored via the flexible control of the energy band structure of different period thicknesses in the same ratio of InAs/InAs_1-xSb_x superlattices.With the built-in electric field and promoted minority carrier transport,the quantum efficiency of the device can be obtained by increasing the absorber layer thickness.The objects of this thesis are as follows:（1）The energy band structure of InAs/InAs_1-xSb_x superlattice materials and the relationship between the optical absorption coefficiency properties and the material structure were investigated using the k·p theory in the Luttinger-Kohn model.Three different superlattice periodic materials with band gaps of 156 me V,132 me V,and 120me V were selected to form a stepped absorber structure with stepped-up valence band energy levels,essentially constant conduction band energy levels,and gradually narrowing band gaps.The detector prepared using this structure has a response and quantum efficiency close to saturation of 1.25 A/W and 20.5%,respectively,and a dark current density of 3.14×10^-5 A/cm² at an applied bias voltage of-0.15 V at a temperature of 100 K at a 2μm thickness absorber.Benefiting from the suppression of the dark current by the wider band gap in the absorber,the dark current at an applied bias voltage of-0.08V is higher than that of the specific detectivity reaches a maximum value with a peak value of 7.41×10¹¹cm·Hz^1/2/W.（2）The photoelectric performance of the designed detector with a stepped absorber is investigated.It is shown that the introduction of the stepped absorber can effectively increase the carrier diffusion length and achieve more efficient collection of photogenerated carriers.In a compared analysis with a 35 MLs uniform absorber detector,the stepped absorber detector can reach a saturation quantum efficiency of 28.2%.And the photodetector’s 50%cut-off wavelength is 10μm at 100 K.At the applied bias voltage of-0.2 V,which is 5.1%higher than that of the uniform absorber device,In summary,this thesis introduced the stepped absorber that can enhance the photoelectric performance of the long-wave infrared detector.