Development of electrically pumped vertical external cavity surface emitting lasers (EP-VECSELs).

摘要

In this thesis design, development and realisation of a substrate emissionudelectrically pumped vertical external cavity surface emitting lasers (EP-VECSELs)udemitting in the 980 nm wavelength range is discussed. Chapter 1 provides audliterature review of the relevant VCSEL and (OP-VECSEL) technology requiredudfor the design of an EP-VECSEL. In chapter 2, different areas of the device designudare highlighted, including electrical and optical performance of the distributedudBragg reflectors (DBRs), active region design, device detuning and antirefiectiveudcoating design.udChapter 3 provides a description of the method used to fabricate EP-VECSELuddevices and focuses on optimisation of different process steps, namely the trenchudetch profile and depth, as well as the contact metalisation. A method forudcharacterising the detuning of a wafer is also presented. In chapter 4udmeasurements of fabricated EP-VECSEL are presented, with a method for theudcharacterisation of the EP-VECSEL material by modulating the output couplerudmirror reflectivity demonstrated. This method is then used to examine the affectudof different substrate dopings on device performance. Data is also presented onudbeam quality, power scaling and thermal properties.udChapter 5 investigates methods for improving electrical aspects of deviceudoperation, with improved nand p DBR designs proposed. In addition, analysis ofudSIMS data for an EP-VECSEL and n-DBR are presented, along with anudinvestigation of the top contact geometry. In chapter 6 a discussion of the QWudactive region is provided, first by analysing the epitaxial material used in chapterud4 and then proposing improvements to the growth process. A comparison of a 3,ud6 and 9 QW active region is then presented, where the trade offs in the optimumudnumber of QWs are examined. Finally, this thesis is summarised and a newuddevice design is proposed from the findings.