High Power Vertical-cavity Surface-emitting Lasers With Small Divergence Angle

Vertical-cavity surface-emitting lasers (VCSELs) are a new type of semiconductor laser which have an optical resonant cavity made by epitaxial growth of semiconductor materials, and the light is emitted orthogonal from the surface. Due to advances in the design and epitaxial growth, as well as fabrication techniques, the performances of the VCSELs, which are used in optical communication, optical connection, optical storage and so on, have progressed steadily. As the output powers improving continuously, the high-power VCSELs are becoming one of the high power laser sources. The VCSELs show many unique advantages in high power applications due to advantages such as circular output beam, low divergence angle, easy shaping and coupling, not subject to COD, convenience in 2D array integration. This paper focuses on high-power 980nm VCSELs devices; study on the design and fabrication of high power VCSELs with small divergence angle.In order to realize lasing, the VCSELs should have high opticak gain and extremely high reflectivity mirrors. We described a calculation method of quantum well gain and calculated the optical gain of the InGaAs/GaAs quantum well. We calculated the reflectivity, absorption, high reflectivity bandwith and the penetration depth of the distributed Bragg reflector (DBR) using the characteristic matrix method, and analysed the way to reduce the heterojunction resistance of the semiconductor DBR mirrors. These analyses are instructive to epitaxial growth of high reflectivity low resistance DBR mirrors.We deduced the expression of the confinement factor, threshold current density, differential quantum efficiency and conversion efficiency, and their impact on the output power. The lasing wavelength, threshold current and the output power of the VCSELs devices under the influence of temperature are discussed.An appropriate fabrication process is designed to produce top-emitting VCSELs devices. The key process was optimized and the pulse anodic oxidation technology is applied to reduce the threshold current density.According to the theoretical analysis and the test results of the devices, we improved the the wafer structure and device structure. We used a wider band gap material of GaAsP instead of the traditional GaAs as a barrier, and the N-type DBR reflectivity is decreased to 99.3%. The highest output power of a single device and 4×4 array device is 2.3W and 1.81W, respectively.The homogeneous current density of the VCSELs can realize by optimized the p-contact diameter and the far-field divergence angle is suppressed from more than 30°to 15°. By using an extra Au layer, the far-field divergence angle of a 4×4 array device is suppressed from 30°to 10°. A linear array with a nonuniform arrangement is designed to realize high power with an approximately Gaussian far-field distribution. The far field divergence angle less than 20°and the device is more suitable for high temperature operation.We reckoned the lifetime of the 4×4 array device at room temperature is up to 5000 hours based on the accelerated aging test results.