Shadow mask MBE for the fabrication of lead chalcogenide buried heterostructure lasers

Laser diodes based on IV-VI-compounds are important sources for tunable infrared radiation in the 3 to 20 Mym spectral region. A major application is trace gas analysis of atmospheric pollutants. Fabrication of buried heterostructure (BH) lasers by molecular beam epitaxy (MBE) improves the spectral and farfield emission properties. Using the materials PbSe, PbEuSe, PbSrSe and PbSnSe, BH lasers were fabricated by directly growing the active stripe through a shadow mask with reduced process duration. The shadow masks were prepared by anisotropic chemical etching of Si(100). The lasers show reduced threshold currents when compared to DH lasers, similar to BH lasers made by a photolithographic technique and also improved radiation patterns. Due to their smooth shape and less surface contamination as compared to their photolithographic counterparts, the overgrowth results show a reduced amount of material discontinuities for the shadow mask lasers.