Strain-Compensating Layers in Stacked Quantum Dot Active Regions

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0074528HuffakerRapid advances have been made in quantum dot (QD) crystal growth and device design to produce lower threshold current density and improved temperature stability in QD semiconductor lasers compared to quantum well (QW) lasers. It is also becoming evident that the QD will have technologically important applications such as extended wavelength (1.0 mm- 1.3 mm) operation of GaAs-based lasers and lateral electronic carrier confinement important for microcavity applications such as low power VCSELs and photonic bandgap defect lasers. Receiving increased attention are lasers and photodetectors operating in the far infrared based on intersubband QD transitions. One of the problems in advancing QD technology, especially at 1.3 mm, is the small gain in the QD active region compared to the QW. A solution to this problem is to stack the QD layers; however, there is a severe limitation on the amount of strained material which can be utilized in the epitaxy.This project will study the development of stacked quantum dot active regions which include strain compensating layers to balance the accumulated strain of the QD stacks. The use of strain-compensating layers is well known in the field of strained multiple quantum well lasers, however it has not yet been investigated for stacked quantum dot active regions. This presents a great opportunity for new experiments in both materials and devices. The project includes the crystal growth of multiple compressively strained InGaAs/GaAs quantum dot active layers separated by tensile strained InGa(As)P layers. The active regions will be studied through X-Ray diffraction and photoluminescence to optimize material parameters. Although the work is applicable to all types of QDs formed by strained layer epitaxy, this project will focus primarily on QDs which emit at the 1.3 mm wavelength. These active regions are applicable to monolithic 1.3 mm GaAs-based VCSELs which are important for signal transmission through silica fibers.