| A quantum cascade laser with a lasing wavelength of 3～5μm has important applications in fields such as infrared gas spectroscopy,medical diagnosis,high-speed communication,security,and optoelectronic countermeasures.The 4.6μm laser source can be used not only for CO gas molecule detection but also as an important light source for infrared countermeasure system.Therefore,research on 4.6μm quantum cascade lasers is of great significance for their applications in both civilian and military fields.Currently,strain compensation technology is mostly used to increase the conduction band step(35)E_cof mid-infrared quantum cascade lasers,thereby suppressing carrier thermal escape and expanding output waveband of the laser.The laser in this paper uses a dual-phonon resonance active region based on strain compensation technology.This paper mainly studies the simulation and manufacturing process of 4.6μm mid-infrared quantum cascade lasers.Firstly the the epitaxial and chip structure were optimized through 3D simulation,then the positive photoresist process and positive photoresist inversion process were designed to achieve the device structure of double-channel stripe and taper.(1)Firstly,the development history of quantum cascade lasers is briefly described,followed by a review of the research progress on 3～5μm high-power quantum cascade lasers,and finally,the applications of quantum cascade lasers in molecular detection,free space laser communication,infrared countermeasures,and other fields are introduced.(2)The principle of quantum cascade lasers is discussed.Firstly,the energy states in the quantum well are analyzed to deeply understand the causes of discrete energy levels in quantum cascade lasers.Then,the analysis of the active region of the classical three-level quantum cascade laser is performed,and it is detailed how to derive and calculate the values of slope efficiency and threshold current of the three-level quantum cascade laser by rate equations.The theories that determine the performance of quantum cascade lasers,such as waveguide theory,dual-phonon resonance active region,cascading effect,and strain compensation technology,are then introduced.(3)The processing theory of semiconductor laser is introduced.Firstly,the process flow and Lift-off process of semiconductor laser are introduced,and then the photolithography technology is introduced,including the classification of photolithography machines and positive/negative photoresists.Finally,the equipment involved in semiconductor laser processing is introduced.(4)The simulation of quantum cascade lasers is studied in detail.Aimed on the key issues that restrict the performance of mid-infrared quantum cascade lasers,this paper improves the heat dissipation of the device by simulating the device structure and materials for a higher output power.Firstly,the performance of quantum cascade lasers with different cladding materials is systematically studied by means of simulation software,and then different device structures are 3D modeled to analyze the distribution of electron concentration in different device structures in detail.Then,the thermal characteristics of different cladding materials are simulated,and finally,the simulation results of the output characteristics,energy band distribution,wavelength,and photon distribution of the device are comprehensively analyzed.The laser material and device structure are optimized based on the simulation results of the device structure.(5)In view of the factors that restrict the performance of the medium-wave quantum cascade laser,such as poor heat dissipation of the ridge device structure and serious lateral current diffusion,the process of realizing the structure of the double-channel strip and taper quantum cascade laser is carried out.First,the positive photoresist inversion process and the positive photoresist process flow are designed,and then the masks are designed and fabricated.Finally,4.6μm strip-shaped and taper-shaped quantum cascade laser of double channel is fabricated. |
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