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Aixtron announces an order for one Close Coupled Showerhead MOCVD system from Tyndall National Institute, based in University College Cork (UCC), Ireland. The order was received in the Q4 2009 and the system will be delivered in the first half of 2010 in a 3x2 inch wafer configuration.
Professor Peter Parbrook, who has been appointed to lead the GaN growth activity at the Tyndall National Institute using strategic funding from Science Foundation Ireland, said, “From our existing Aixtron reactors we are very familiar with the quality of performance and engineering available with their tools. There are many reasons why we opted for a CCS® reactor for our GaN programme: for instance the flexible reactor configuration which includes gap adjustment. Plus we can work with a range of different substrate sizes to suit our various research projects. Inherently, the tool also has high growth uniformity and we are looking forward to using the ARGUS pyrometric system to give us precision in-situ monitoring and process control.”
The growth tool will complement Tyndall’s existing expertise in the theory of GaN photonic materials and fabrication of GaN based devices. The new system will be used to support work on advanced GaN technologies including growth of GaN / (Al, Ga, In)N-based materials for opto-electronic and micro-electronic devices with a focus on high temperature growth of AlGaN structures.
Breakthrough in power and efficiency puts DFB laser in competition with the FP
Researchers from the Ferdinand-Braun- Institute in Berlin have developed a 976nm DFB laser emitting 11W and having a power conversion efficiency of 58%. This is reported to be the smallest ever difference between a DFB laser and comparable FP laser which had an efficiency of 67%.
The difference is attributed to be due to the relatively lower slope efficiency of the DFB. However, extrapolation of differential quantum efficiency calculations suggests that the power conversion difference between the DFB and FP lasers may be further reduced by using a smaller grating coupling coefficient k.
The enhanced power and efficiency in the new design are attributed to the InGaAs DQW active wavelength, the 2.1mm thick Al15Ga85As waveguide and a two-step grating fabrication process. This improvement would make the DFB far more attractive to the tuneable, pumping fibre and solid-state laser markets.
Although they possess distinct advantages over their Fabry-Perot counterparts, having extremely narrow line widths and superior spectral stability, the conventional DFB laser suffers from comparitively low power and power conversion efficiency, typically 8W and > 73% efficiency.
The GaAs-based lasers investigated in this study were grown using low pressure MOVPE and the InGaAs active region in the DFB laser (which is periodically structured as a diffraction grating) has GaAsP barriers. The grating in such devices is constructed so as to reflect only a narrow band of wavelengths, and thus produce a narrow linewidth of laser output.
The waveguide composition in this DFB laser was optimised for low voltage and leakage current, high carrier mobility and reduced oxidation. A novel vertical design with a far- field emission angle of 450 was targeted by optimizing the refractive index profile and adjusting the waveguide thickness and asymmetry.
The design includes a 20nm InGaP etch-stop layer 630nm above the DQW enabling the wafer to be patterned using holography and lithography, after which a 2nd order grating is formed. After the subsequent overgrowth of the waveguide, a high refractive index contrast
June
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