MBE Regrowth Over a Selectively Undercut GaAs Masking Layer

Abstract

We describe the use of molecular beam epitaxy (MBE) for regrowth over a photolithographically defined GaAs shadow mask to fabricate a buried etched void surrounding a vertical-cavity surface-emitting laser (VCSEL). The initial MBE growth consists of a GaAs etch stop layer, followed by an Al_0.67Ga_o.33As spacer layer, and then a GaAs capping layer. After the initial growth, various diameter openings ranging from 2 to10 gtm are photolithographically defined in a photoresist layer, and the top GaAs layer is selectively etched. The exposed LTAlGaAs layer is next selectively etched with the etch time adjusted to undercut the top GaAs layer to create a shadow mask. An MBE regrowthis then performed which consists of alternating layers of GaAs and AlAs. Scanning electron microscopy, surface profiling, and optical microscopy are used to characterize the regrowth.

We have used this shadow masking technique to realize a buried etched void surrounding the optically active part of a VCSEL. A continuous wave room temperature lasing thresholdof 0.47 mA for a 4 [tm device has been achieved, which to our knowledge is the lowest continuous wave room temperature threshold yet reported for a VCSEL.