Application Of Wet Selective Oxidation In VCSEL

The vertical cavity surface emitting laser (VCSEL) is a new type ofopto-electronic device with several important advantages compared to conventionaledge-emitting semiconductor lasers. Comparison between VCSELs and conventionallasers along with a brief description of the VCSEL developed at the Suzhou everbrightphotonics Co.Among the several options for current confinement we will concentrate on arelatively recent one which uses wet selective oxidation of ALAs-layers. A completeoverview of what can be found in literature about this relatively new oxidationprocess is presented and will act as an introduction to two main aspects of intra-cavitycontacted VCSELs treated in this master’s thesis:A general insight into the wet selective oxidation of ALxGal-xAs layers in order toobtain a reliable and uniform process which transforms epitaxially grown and highAL-content compounds into stable dielectric material. This process is exploited forthe current confining in the intra-cavity contacted VCSELDevelopment of the technological steps required for the realization of aoxide-based Distributed Bragg Reflector (DBR) mirror for visible light applications (A,=650nm). Concerning the first task of this project, several MBE-grown samplescontainingmultilayers GaAs-ALAs were prepared by using wet or dry processtechniques. Oxidation of AlAs-layers was carried out in a quartz furnace at400-450°Cin a saturated environment; s ince the oxidation rate of AlxGal-xAs strongly increaseswith AL-content this process is very selective and only the AlAs-layers aretransformed into a mechanically and thermally stable oxide (polycrystalline’Y-AL2O3)While the vertical oxidation of ALxGal-xAs shows a diffusive character andsaturation for long oxidation times, the lateral oxidation remains reaction-limited forall of the times inspected. This behavior is probably due to the formation along theoxide/semiconductor interface as a result of the contraction of the oxide: the canalsare responsible for the fast transport of the oxidizing gasses to and from the oxidationfront.Although the oxidation process is still not fully controlled due to the largenumber of parameters which affect the mechanism and the kinetics, the experimentalobservations carried out during this project will allow a better awareness of the wholeprocess when new material will be available.