Theoretical Analysis Of Thermal-Field And Its Coupling With Electricity And Optical-Field In Vertical-Cavity Surface-Emitting Lasers

Vertical Cavity Surface Emitting Lasers (VCSELs) have been studied extensively in the field of optoelectronics over the past few years. The principle advantages of VCSELs over conventional edge-emitting lasers lie in ultralow threshold current, small far-field divergent angle, high modulation frequency, potential for wafer level testing and the ease for single longitudinal mode operation and two-dimension integration. As a result they show considerable promise for applications such as optical fiber communication, parallel optical interconnects, optical information processing and neural networks, etc.A direct coupling theoretical model in quasi-three-dimension for the gain-wave guide vertical-cavity surface-emitting lasers has been created in this paper. With the finite-difference method, self-consistent solutions for the Possion's equation, injected current density, carrier concentration, optical field and thermal conduction equations have been realized to study the thermal-field properties, the coupling of electricity, thermal and optical-fields, and the influences of N-DBR and double oxide-confining regions on the characteristics of VCSELs. With numerical calculations, the influences of device structure, material parameters and operating conditions on the distributions of the equipotential line, current density, carrier concentration, optical field and temperature profiles have been investigated, and the interactions between the correlative characteristics have been studied at the same time.The main work can be summed up as follows: Firstly, we studied the thermal-field properties of VCSELs, and analyzed the influences of current spreading, material parameters and operating conditions on the temperature distributions. Secondly, we began with the electrode voltage and calculated the equipotential s distributions, compared the distributions of voltages and current densities in different depths of VCSELs, and then studied the influences of the oxide-confining region with different position or thickness, and the different sizes of the gain-guided aperture and emitting window on the distributions of the injected current density, carrier concentration and temperature in the active region. Thirdly, we realized the coupling of electricity, optical and thermal-fields, worked out the threshold voltage, calculated the distributions of the injected current density, carrier concentration and temperature under different offset voltages, and analyzed the impacts of temperature profile and carrier density on the refractive index, Fermi levels and optical-field. Finally, we gave the equipotential line distributions with considering N-DBR and double oxidized-confining regions, and analyzed theinfluences of N-DBR and double oxide-confining regions on the distributions of the current density, carrier concentration, temperature and optical-field.The results show that if N-DBR is neglected, the theoretical calculations are in good agreement with the references. But our results also indicate that N-DBR has very important influences on the properties of VCSELs and if it is not considered, there must be some errors. And double oxide-confining regions offer a method of decreasing threshold current and controlling high order modes.