Research on Blue and Near Ultraviolet Diode Lasers

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9726938 Nurmikko The PI proposes a research program whose objective is to focus on specific areas of basic and applied semiconductor science to aid in the the continued development of the group III-nitride based semiconductor blue lasers and extension of such devices to the near ultraviolet. Further progress in this field of vast technological potential requires systematic scientific efforts. The PI identifies and addresses two critical areas in the proposed program: (a) the study of optical gain and related radiative processes in the nitride quantum wells for optimizing the active region of the laser and implementing a low threshold device design, and (b) development of understanding at a microscopic level of the p-type ohmic contact problem. In addition to the overall idiosyncracies of a widegap semiconductor, both of these problem areas are impacted by the complex and rich microstructure of the nitride heterostructures. In the planned work we thus also look for key links between the crystal microstructure and optoelectronic properties which are presently poorly understood. Apart from our early results on nitride-based diode light emitters, the PI takes advantage of our experience with bluegreen II-VI semiconductor lasers where the issues of gain, device design, and contacts were successfully pursued by the PIs for advancing these quantum well diode devices. Significant differences and distinct challenges do, of course, exist in the nitrides; however, given the common features that are shared by wide bandgap semiconductors at a fundamental level provides a very useful base of comparison for quantitatively and scientifically meaningful comparisons, The proposed research takes advantage of special capabilities and techniques adapted to the study of both nitride-based heterostructures and diode laser devices. For example, advanced laser-based spectroscopic techniques, including ultrafast real-time spectroscopy will be applied to study the optical gain and dynamics of a high density lo w dimensional electron-hole pair in a disordered system such as the InGaN QW where electronic localization effects are important. The techniques include high spatial resolution probes such as near-field optical microscopy. For the p-type contact studies, in-situ deposition of metallization and InN heterostructures in UHV environment is proposed as a means to study the microscopic properties of the metal-nitride interface in order to optimize a low resistance contact for diode laser application. ***