GaAs/AlOx micropillar fabrication for small mode volume photon sources

Micropillar devices have shown promise as single photon sources for applications in quantum key distribution as well as single photon metrology and fundamental science. For higher temperature operation (77  K), a high quality factor (Q) cavity and a small modal volume are necessary for enhanced spontaneous emission. Although high Q's have been demonstrated, achieving small modal volumes is difficult due to the limited index contrast available from the lattice-matched Bragg layers of GaAs and AlGaAs. However, by wet thermal oxidation of AlGaAs or AlAs layers to amorphous aluminum oxide (AlOx), very high index contrast layers can be obtained. This allows for high reflectivity mirrors with fewer Bragg pairs, resulting in reduced mode volume from reduced penetration of the optical mode within the mirror pairs. The authors apply this method in a GaAs/Al_0.95Ga_0.05As material system and describe a fabrication process for such devices, utilizing a BCl₃:Cl₂:Ar etch. Photoluminescence measurements of micropillars with three top and five bottom layers are demonstrated. They are measured to have Q's of 200–400 for approximately 1–3  µm diameters, respectively. These results indicate that high Q devices may be possible while simultaneously reducing the modal volume. ©2010 American Vacuum Society