Fabrication of Low Threshold Voltage Microlasers

Abstract

We have reduced the voltage required for threshold in vertical cavity surface emitting lasers (VCSELs) to 1.7 V. Molecular beam epitaxy (MBE) was used to grow 30 pairs of n-doped Al_(0.15)GaAs/AlAs bottom mirrors and the active p-n junction with a 1 μm p-doped top contact. 12 pairs of alternating SiO_2/Si_3N_4 layers formed a high-reflectivity mirror which was used to complete the laser cavity. We have evaluated these reactive sputter-deposited mirrors by using finesse measurements in resonator structures, and obtain reflectivities of above 98% in 9.5 pairs. Individual laser elements were defined by ion etching through the p-n junction, followed by planarization with SiO_2 to define the current path. Then, Au-Zn p-contacts were deposited and alloyed for lateral current injection. Finally, another ion milling step was used to isolate individual contacts. Lasers with widths ranging from 7.5 μm to 25 μm were fabricated and measured.