The Study Of Semiconductor Quantum-well Lasers Theory Model And Application In The Computer Simulation

With the development of optoelectronical technology, semiconductor quantum-well(QW) lasers have been widely used in a lot of fields. In order to develop and apply QW lasers better , a great deal of theoretical study has been done. The development of computers makes the 1D,2D and quasi-3D numerical analysis of QW lasers develop rapidly. The purpose is to simulate lasers and optimize parameters on the base of accurate theory models. Finally, experimental expenses can be reduced. With the idea, we start this work. Firstly, the theory model improvement and energy band structure are studied. Then, the design method of the QW lasers CAD system is introduced. Finally, some examples and analysis results are presented. In order to analyze the effects of quantum size, tunneling and quantum Stark, on the base of classical device equations(including Poisson's equ., electron and hole continuity equs., wave equ., thermal conduction equ., and photon rate equ.), the Schrodinger equation is introduced into the theory model that is used to analyze a QW laser in a transverse direction. And the equation will be solved in the whole QW region without a simple flat approximation, which makes the accurate carriers distribution obtained and presents compared results with experimental ones. The further work is the combination of the transverse model and the coupling wave theory, which provides with a new quasi-3D model used to, considering quantum effects in a 3D space , simulate QW DFB or DBR lasers. A great deal of work has been done arithmetically. A self-consistent method including the Schrodinger equation is presented in 1D and 2D transverse analysis of QW lasers. All eigenvalues and wave functions can be obtained in the whole QW region, and the density of carriers can also be calculated easily. Normally, in a quasi-3D simulation of DFB or DBR QW lasers, transverse and longitudinal calculations are carried out time after time, and it takes a long CPU time. For a fast calculation, a new parameter fit of the transverse gain, loss and effective index is presented. The results obtained from the fit formulas will be used in the longitudinal calculation directly, which makes the calculation quantity reduce from 3D to 1D. About ninety percent of time is saved. In the longitudinal simulation, a vector method is used, which presents not only the solutions of multi-mode, but also a stable arithmetic suiting TMM. Another work is about energy band analysis. After putting others'achievements together, complete 3-band,4-band,6-band and 8-band k?p coupling energy band models are presented. The package function method used to solve the Hamiltonian matrix is also introduced. The band gap calculations of multi-element and strained material system are carried out. In order to analyze energy band structure systematically , the calculation of band offset is made, using the Harrison's model and the Model-Solid model respectively. We find that the calculation using the Harrison's model gives an accurate result, but no enough material data can be obtained . Considering InGaAs/InP QW system, the valence band structure, energy state density, linear gain function and differential gain have been analyzed in detail. We find that gain spectra resulting from Gauss shape function is almost the same with that from Lorentzian shape function. On the base of consummating theory models, QWCAD system has been designed. In QWCAD system, some important methods have been used to describe a laser device, such as layer unit and segment unit definition. In the program design, mixing language and multi-thread technology are used, which solves the communication problem between the user and the computer. QWCAD system includes QW lasers transverse 1D,2D simulation module, energy band structure analysis module, band offset calculation module, waveguide optimization module, longitudinal 1D,quasi-3D simulation module and active zone optimization module. Using these modules, you can analyze or calculate the threshold current , L-I,V-I, optical mode, temperature distribution and small signal AM/FM modulation response. They can also present carriers distribution, photon distribution, energy band structure , energy state density and material gain. All systems have a friendly interface and strong function. Compared with other QW CAD software, QWCAD's edit function is limited, but the model is special. Using energy band analysis module, we have studied the relations between the well width, gain and composition. And some useful formulas which can reduce calculation quantity are presented. We examine the strain tensor in InAs/GaAs/InP and InAs/InP QDs using a valence force field model, and use a five-band k?p model to obtain the electronic spectra. We find that the GaAs tensile-stained layer affects the position of room temperature PL peak. The redshift of PL peak of InAs/GaAs/InP QDs compared to that of InAs/InP QDs is explained theoretically. Using active zone optimization module , we have analyzed a -0.78%compressively strained QW structure. The active region consists of 5.4nm-thick InGaAlAs wells and 5.7-nm-thick InGaAlAs barriers. We obtain the optimized well number(7-8)and the optimized cavity length(550-650μm), which results in a threshold current of 10-15 mA, a threshold current density of 600-650 A/cm2, and a maximum operating temperature of 550-560 K. When well number changes between 10 and 12, relaxation frequency will be 10-18GHz. Carriers distribution of an InGaAs/InP QW laser have been calculated by transverse analysis module, and the difference of results between two models is presented. We find that the model including Schrodinger global solutions presents the threshold current of 10mA-12mA when well number changes from 7 to 8 and cavity length from 300μm to 400μm. The simple model presents the threshold current of 13mA-16mA when well number changes from 6 to 7, cavity length from 400μm to 500μm. The responses of AM/FM modulation from the two models is also different and the modulation response frequency from the model including Schrodinger global solutions is higher. The longitudinal modes and the responses of AM/FM modulation of a 3PS-DFB QW laser are analyzed by the quasi-3D simulation module. The results show that PS is helpful to the output of SLM and suppression of LHSB.