A Process for Transferring and Patterning InAs Quantum Dot Optical Gain Media for HAMR Near Field Optical Sources

We report a process by which a 270 nm layer of optical gain medium is transferred to a dielectric substrate via a flip chip process and patterned into disk structures suitable for microcavity lasers. This process is anticipated to have application to near field transducers for heat assisted magnetic recording (HAMR). Specifically, the gain medium consists of 5 layers of InAs quantum dots embedded in GaAs. The transfer process was accomplished by depositing a series of etch stop layers on the GaAs substrate before the QD gain layers, and then using these etch stop layers in a polishing and etching process to remove the substrate of the gain medium. To support the gain medium during this removal, the GaAs wafer was flipped onto an epoxy layer that had been applied to a glass wafer, where the gain medium layer was eventually left in place and separated from the substrate. This gain medium layer on epoxy was then patterned using photolithography and ion milling. Photoluminescence studies show little effect on the optical properties resulting from the transfer and the patterned devices show optical mode structures consistent with an approach to lasing. However, the epoxy substrate is revealed to be too poor a thermal conductor for optical pumping to reach the lasing threshold. Detailed analysis of the temperature rise upon illumination combined with literature values for the lasing threshold pump levels suggests that substrates with thermal conductivities of around 10 W/m-K are required for the process to yield working lasers.