All-epitaxial-apertured GaAs-based vertical-cavity surface-emitting laser

Abstract

An all-epitaxial process is described for obtaining an intracavity aperture in GaAs-based vertical-cavity surface-emitting lasers (VCSELs) that lead to simultaneous current and optical confinement. The laser structure starts with 30 pairs of n-type GaAs/AlAs bottom DBR mirrors, a full-wave cavity including three 6nm In0.2Ga0.8As quantum wells at the center, and 1.5 pairs of p-type GaAs/AlGaAs DBR mirrors. A tunnel junction is deposited thereafter, which includes AlGaAs etch-stop, 30nm p+ (Be = 5×1019 cm-3) GaAs, 10nm n+ (Si = 5×1019 cm-3) In0.1Ga0.9As, and 30nm n+ (Si = 1×1019 cm-3) GaAs. Apertures are defined by removal of the tunnel junction layers outside the aperture via ex-situ lithography and wet etching. The VCSEL structure is completed by an MBE regrowth of 15 pairs of n-type GaAs/AlAs DBRs. Simple post-grown processing includes metal ring contact deposition and device isolation (wet-etching through the cavity.) The current confinement in the area far from the aperture is shown to be excellent from the measurement of the same-size dummy mesas and metal contacts next to the working devices on the same wafer. At room temperature, a 10 μm circular-aperture VCSEL lases under pulsed current injection with a threshold current of 2.6mA. Some limitations in the continuous wave operating characteristics will be described and are believed to arise from Be diffusion. Replacing Be with a less diffusive C dopant can greatly improve the device performance.