Short-wavelength InAl(x)Ga(1-x)P quantum well lasers and InP quantum dot coupled to strained InAl(x)Ga(1-x)P quantum well lasers grown by MOCVD
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III-phosphide self-assembled quantum dot (SAQD) structures offer the ability to realize injection lasers operating in the visible wavelength region from as short wavelength as yellow to deep red with superior performance characteristics, such as low threshold current density and high characteristic temperature. Previously, results of InP QD lasers grown by MOCVD that lased optically pumped pulsed at 300K and continuous-wave (CW) at 77K were described. Further, by incorporating an auxiliary InGaP quantum well (QW) coupled to the QD layers (QW + QD) by a InAlGaP barrier layer due to resonant tunneling, novel QW + QD lasers can be realized with better carrier collection, better thermalization of carriers, and lateral rearrangement of carriers in the QWs; thus giving considerably better laser performance characteristics. The effects of coupling the InP QD states to the electronic states of InGaP QWs will be studied especially with regards to improving device performance and decreasing the wavelength of operation. Further, the effect of adding strained InGaP QWs underneath InP SAQDs will be studied by performing surface morphology analysis. There are several different parameters that affect the growth and the QD areal density was optimized from about 1x1010 cm-2 to as much as 3x1010 cm-2. These InP QD coupled to InGaP QW active regions have been incorporated into various laser separate-confinement active regions. The continuous-wave 300K laser operation of an In0.49Al1-xP/In0.49(AlxGa1-x)0.51P/In0.49Ga0.51P/InP QD coupled to QW laser diode was demonstrated lasing at a visible wavelength (654nm); this is the first reported CW 300K injection laser using InP QDs. Further, by using further novel devices, an InP QD coupled to InGaP QW injection laser was grown and demonstrated at 300K with a lasing wavelength of 607nm, the shortest reported wavelength for any laser diode grown on GaAs. Based on various recombination spectra, it is obvious that the gain peaks at the quantum dot excited state, thus further indicating the coupling of the quantum well states to the quantum dot states. The growth and properties of these novel QW+QD injection lasers will be discussed.