Research On Photoelectric Regulation And Performance Optimization Of Long/Very Long Wavelength Infrared Quantum Well Photodetectors

Infrared detectors are an indispensable and important part of infrared detection technology,from the first practical Pb S infrared detector during World War II to the third-generation large area array,small pixel,low cost,dual-color and multicolor infrared photodetectors that are booming today,the infrared detector has gone through a history of nearly 80 years.Quantum well infrared detector(QWIP)is the third generation infrared detector,which works based on the intersubbands transition(ISBT)in the conduction band.The energy of the transition between sub-bands is just in the infrared band,therefore,it shows great application prospects in the field of infrared detection.The absorption peaks of Group?-?compounds can be adjusted in the middle and far infrared bands,which can be used for focal plane array,two-color and multi-color detection.Compared with the Hg Cd Te detector,the?-?group quantum well infrared detector represented by Ga As/Al Ga As has the advantages of large area uniformity,mature material growth and device preparation process,high yield,short response time,etc.The research hotspot in the field of infrared detectors has been widely used in the field of defense military and sky detection.However,it also has the problems of non-absorbing normal incident light and low quantum efficiency.Thus,study on improving the performance of QWIP is the most important research directions of the quantum well infrared detector.The work of this thesis focuses on the performance optimization of quantum well infrared detectors.As a photodetector,its performance can be improved from both electrical and optical aspects.The electrical regulation is to optimize the working mode of device and electronic transport characteristics of the material.Based on this,we have optimized the growth mode of the In Ga As/Ga As quantum well material,and the electron transport characteristics of the material as well as the performance of the quantum well detector are both greatly improved.Optical regulation mainly improves efficiency of optical coupling by integrating various optical coupling structures.Based on optical control,the metal-medium-metal(MIM)microcavity widely used in the field of focal plane array field has been optimized,and a new type of three-dimensional self-rolled-up optical coupling structure has been designed and successfully grown and prepared,the performance of the detector was optimized from the perspective of enhanced light absorption.The main work consists:1 In Ga As/Ga As very-long wavelength QWIP materials with a wavelength of 15?m were grown by different MBE methods,and the effects of different MBE growth modes on QWIP performance were studied.A material with high crystal quality and high external quantum efficiency is obtained by a continuous low temperature method.By performing photoelectric measurements,it is found that the devices obtained by continuous low-temperature growth showed better performance than devices obtained by temperature-changed growth method,which are characterized by lower dark current and higher background limited performance temperature (TBLIP).The peak responsivity increased by 38 to 5.67 A W at 20 K,indicating high performance of the In Ga As/Ga As QWIP.Our results also show that the photoconductive gain of a device operating based on B-B mode can be adjusted by changing the applied bias voltage,which provides guidance for the preparation and development of high-performance and very long-wave QWIP.2 To optimize the performance of the quantum well infrared detector from the perspective of optical coupling,we have designed a new type of long-wave self-rolled quantum well infrared detector.Ga As/Al Ga As quantum well infrared detection material containing strained layer of In Al Ga As(In Ga As)was successfully epitaxy using molecular beam epitaxy system.The fluorescence intensity peak of the rolled quantum well is increased by 4 times,and the suspended hollow microtubes form a Fabry-Perot cavity,and the emission peak of the quantum well at 820 nm resonats in the cavity.The fluorescence intensity peak of the rolled quantum well is increased by 4 times.In addition,both black body response and photocurrent response spectrum of the device were tested,the peak wavelength of the tubular QWIP is 8.6?m.Such a rolled QWIP achieves direct absorption and enhanced light response to infrared normally incident light.Infrared radiation penetrates the thin wall and travels to the hollow area of the microtube,and reflections by three times at the surface of the inner wall allow the device to absorb the infrared light three times to achieve the enhancement of light response and fluorescence intensity.At the temperature of 30K,its peak responsivity and quantum efficiency are both enhanced by 2.7 times compared to standard devices,reaching 48.2 m A/W and 1.9%,respectively.3 caused by metal structures widely used in optocouplers and heat dissipation in integrated devices,we have proposed a new type of efficient dielectric-microcavity coupled terahertz quantum well infrared photodetector(DMC-THz QWIP),where THz quantum well active region is sandwiched between periodically heavily doped Si and Ga As upper and bottom electrode layers.Like metals in visible light,heavily doped semiconductors also have high plasma frequencies at mid-infrared and far-infrared wavelengths.The inter-subband absorption spectrum and electric field distribution of DMC-THz QWIP were calculated by finite-difference time-domain (FDTD)method.Our results show that under the optimized structure,the frequency of the surface plasmon can be tuned to resonate with the microcavity.This DMC-THz QWIP microcavity structure can effectively enhance the inter-subband absorption,and the enhancement mechanism is similar to MIM.When the doping concentration of the Ga As electrode layer exceeds 10¹⁹ cm^-3,the inter-subband absorption of DMC-THz QWIP at the response wavelength is one order of magnitude higher than that of a standard 45-degree device(STD).The absorption rate can be enhanced 20 times as the doping concentration is 3.2×10¹⁹ cm-3.In addition,the angle of the incident light only affects the intensity of the absorptivity,indicating that the designed device has nothing to do with the periodic surface structure.