| The need for low cost, high speed telecommunication and datacom sources demands the maturation of long wavelength vertical cavity lasers (VCLs). Long wavelength emission is desirable, as it is compatible with existing single mode fiber dispersion and loss minima. In order for long wavelength VCSELs to establish a cost advantage over uncooled distributed feedback lasers (DFBs), VCSELs must operate reliably over a wide temperature range. The difficulty in achieving suitable thermal behavior in long wavelength systems is manifested in low characteristic temperatures, and attributed to the high Auger recombination and intra-valence band absorption characteristic of low energy gap materials. A second major obstacle is the problem of finding a lattice matched mirror system capable of achieving the high reflectivities necessary for VCSEL design. This places stringent requirements on the design and optimization of the VCL structure. Wafer fusion has been used to combine the InP-based active region with high reflectivity GaAs-based mirrors, circumventing the problem of lattice matching. With this technology, the tradition of high performance LW-VCLs at UCSB was founded. At some point, however, the technology that enabled these devices also became their greatest limitation: the fused junction. This thesis is an in depth examination of an interface: its formation, its properties, and ultimately its role in the creation of state of the art VCSEL technology. The chemistry and microstructure of the fused interface are examined in order to determine the mechanism of fusion and optimize the structure of the interface. The electrical and optical impact of the fusion process and resultant interface on device performance is explored. In addition, two major additions to the device design were made capitalizing on the 3D design freedom afforded by the fusion process. The first attempts to incorporate a defect blocking superlattice at the fused interface to improve the gain of the active material. The second is the development and incorporation of selective area fusion for both current and carrier confinement into the device design. A deeper understanding of the nature of the fused interface allows the device designer to at once embrace the technology and work within its limitations. In conclusion, the state of the art device performance is presented, including record low threshold (0.8mA), high temperature (74°C), and small signal modulation bandwidth (7GHz) for LW-VCLs. |
