Quantum-dot-based membrane external-cavity surface-emitting laser (MECSEL) for the 650 to 760 nm range
Final Report Abstract
The main goal of this project was to realize a new kind of semiconductor‐based laser system that overcomes several problems which occur in conventional semiconductor lasers. The material system we chose to work with is aluminum‐gallium‐indium‐phosphide. Nearly all red light emitting semicon‐ ductor‐based devices like simple light‐emitting diodes or laser diodes for DVD drives and laser pointers are made of this quaternary material. For low emission powers in the range of milliwatts, these devices have proven their performance and reliability for many years. Unfortunately, if more laser output power – e. g. in the Watt or even multi‐Watt level – is required, this material system suffers from its high thermal sensitivity. First laser results, based on a concept which could theoretically deliver high output powers while keeping a very good beam profile, have been presented in 1997. Here a thin semiconductor disk is optically pumped by other laser devices. The benefit of optical pumping is that the high Ohmic resistance, which would be responsible for heating up the device intrinsically, if electrically pumped, can be circumvented. Also a pump wave‐length can be found which reduces the heat load to a physically allowed minimum. Additionally, a heatspreader, a transparent device with high thermal conductivity, can be placed on the surface or the backside of the semiconductor device. In this way it was possible to reach output powers in the Watt regime in the aluminum‐gallium‐indium‐phosphide material system with the semiconductor disk laser. But as this was not sufficient yet new ground had to be broken on thermal management. The best, which can be done then, is to bring the just a few hundred nanometer thick active region – where the heat is generated – on both sides in direct contact with a diamond heats spreader to get the best heat extraction out of the active region which is physically possible. At the same time this simplifies the growth process considerably because only a membrane consisting of the active layer has to be grown. The growth of a semiconductor based Bragg reflector or any other layer except the active region (and if necessary an etch‐stop layer for chemical purposes) is obsolete. To realize such a “semiconductor membrane vertical‐external‐cavity surface‐emitting laser” a wet‐chemically etching process had to be developed to selectively remove the Gallium‐Arsenide substrate, but to keep the active region. After transferring this semiconductor membrane to the first diamond heatspreader, the second heatspreader is placed on top of both. The whole package with the membrane in between is then placed in a sample holder especially designed for this purpose and then mechanically squeezed. This semiconductor gain package placed in a linear laser resonator, shows laser emission. Very first results show outstanding and for future projects very promising performance values. Yet another benefit of this new laser concept came to our attention. The six‐micrometer‐thick dielec‐ tric mirror inside the structure is, as already mentioned, not used anymore and therefore has not to be produced. This simplifies the whole production process of the semiconductor part and makes it even cheaper. Also the developing time needed to design, grow, characterize and re‐grow a new semiconductor membrane was drastically reduced and allowed us to progress much faster once this membrane process had been established. Finally, the concept of the diamond sandwiched semiconductor membrane laser could be successfully realized and is now on its way to a high‐power and high‐brilliance semiconductor laser.
Publications
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“Strain compensation techniques for red AlGaInP‐VECSELs: Performance comparison of epitaxial designs”, J. Cryst. Growth 370, 208 (2013)
T. Schwarzbäck, H. Kahle, M. Jetter, and P. Michler
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“High optical output power in the UVA range of a frequency‐doubled, strain‐compensated AlGaInP‐VECSEL”, Applied Physics Express 7, 092705 (2014)
H. Kahle, R. Bek, M. Heldmaier, T. Schwarzbäck, M. Jetter, and P. Michler
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“Comparison of AlGaInP‐VECSEL gain structures”, J. Cryst. Growth 414, 219–222 (2015)
S. Baumgärtner, H. Kahle, R. Bek, T. Schwarzbäck, M. Jetter, and P. Michler
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“Enhanced Efficiency of GaInP Disk Laser by In‐Well Pumping”, Optics Express 23, 2472‐2486 (2015)
C. M. N. Mateo, U. Brauch, T. Schwarzbäck, H. Kahle, M. Jetter M. Abdou‐Ahmed, P. Michler and T. Graf
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“2.5 W continuous wave output at 665 nm from a multipass and quantum‐well‐pumped AlGaInP vertical‐external‐cavity surface‐emitting laser”, Optics Letters 41, 1245‐1248 (2016)
C. M. N. Mateo, U. Brauch, H. Kahle, T. Schwarzbäck, M. Jetter M. Abdou Ahmed, P. Michler, and T. Graf
