Design, simulation and fabrication of nanostructured IR vertical-cavity surface-emitting lasers with graded Bragg interfaces

VCSEL, or Vertical Cavity Surface Emitting Laser, is a semiconductor microlaser diode which emits light in a beam vertically from the surface of a fabricated wafer, and offers significant advantages when compared to the edge emitting lasers currently used in the majority of fiber optic communications devices. VCSELs can be fabricated efficiently on a 3-inch diameter wafer. Even more important, the ability to manufacture these lasers using standard microelectronic fabrication method allows integration of VCSELs with other components on the same wafer.; The present work introduces an optimized VCSEL with graded transition bands inside the Distributed Bragg Reflecting Mirrors (DBRs) designed in order to achieve the tradeoff between the number of DBR layers and the low threshold current of the laser. Based on the Al_xGa_1−xAs/GaAs system and with graded Distributed Bragg Reflectors (DBRs), we have demonstrated a successful VCSEL operation at 850–860nm. Design, simulation, fabrication and characterization results are presented. The structure optimized had 39 pairs in the n-DBR stack and achieved a low threshold current of 1.6mA. The device was fabricated with MBE growth, oxide confinement and RIE for MESA definition. The experimental results and physical characterization of the device are also reported to fully understand the VCSEL performance. The threshold current and other parameters predicted by the simulation are in good agreement with experimental results. The electron discrete energy levels are also calculated based on quantum mechanical solution of the appropriate wave equations and boundary conditions.