9805760 Neumark This project aims for greater understanding of bipolar doping in wide bandgap semiconductors. A primary aim of the project to investigate nonequilibrium effects on doping during MBE growth, and to use the insight gained to improve doping. ZnSe and related alloys (with mainly nitrogen doping) will be used as a test system. A further aim of the project is to apply the resultant understanding to improve doping in ZnBe, and possibly ZnCdBe chalcogenide alloys, since these alloys are candidates for potential improvements in device lifetimes of ZnSe-based blue-green diode lasers. Specific aspects of MBE growth planned for investigation are planar doping, changes in the metal/chalcogenide ratio, and/or changes in crystallographic orientation. A further objective is to study and possibly eliminate DX centers by use of the planar doping technique. Planar doping will be used with both the dopant and a different chalcogenide (such as Te for ZnMgSeS) to modify the local environment of such centers so as to eliminate them from some systems where they now exist--it has been reported that simultaneous Te/N planar doping gives not only almost an order of magnitude improvement in hole concentrations in ZnSe, but also changes the ionization energy to close to the ZnTe value. Elimination of DX centers would be a major technological and fundamental breakthrough. In addition to the study of growth, it is also planned to coordinate growth with determination of compensating species. Considering non-equilibrium aspects of doping, different compensating species may dominate under different conditions. Compensating species resulting from various growth approaches will be studied, primarily via luminescence, positron annihilation spectroscopy, and optically detected magnetic resonance. %%% The project addresses basic research issues in a topical area of materials science having high technological relevance. The research will contribute basic materials science knowledge at a fundamental level to important aspects of electronic/photonic devices. Experimental tools are now available to allow atomic level observation of materials defects and their origins which when better understood will allow advances in both fundamental science and technology. The basic knowledge and understanding gained from the research is expected to contribute to improving the performance and stability of advanced devices by providing a fundamental understanding and a basis for designing and producing improved materials, and materials combinations. An important feature of the program is the integration of research and education through the training of students in a fundamentally and technologically significant area.
