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John O | June 2017

Researchers explain how heat sink sandwich enhances semiconductor laser


researchers from the stuttgart research center of photonic engineering (scope) at the university of stuttgart (germany) have developed a method of sandwiching quantum well (qw) or quantum dot (qd) membranes between diamond or silicon carbide heat sinks to maximize laser cooling, which removes the need for a reflectors mirror and extends the wavelength performance of semiconductor disk lasers.

 


this article explained a new membrane between heat sinks maximizes
laser cooling. (wikimedia commons)

 

this research was presented on laserfocusworld.com. the researchers explained, “the symmetric transmissive sandwich configuration of this semiconductor membrane laser minimizes thermal effects on the laser resonator and the beam quality, while the absence of the distributed bragg reflector (dbr) mirror extends the possible range of material combinations and wavelengths.”

 

in order to create the sandwich of materials, the research team created a method for detaching the active region from the substrate and mounting it between the heat sinks. this layer was typically several hundred nanometers thick.

 

“to accomplish this, after epitaxial growth of the active region and the necessary sacrificial layer, the wafer is cleaved into pieces, and the epi-side glued to a silicon carrier,” the article continued. “an aluminum arsenide (alas) sacrificial layer between the substrate and active layers allows complete removal of the substrate by wet chemical etching.

 

“in a second etching process, this sacrificial layer is then removed, leaving only the active region on the silicon carrier wafer. after dissolving the glue, the then-free-floating membrane can be ‘picked up’ by one of the heat sink substrates.”

 

the heat sink with membrane on top is moved to the sample holder and a second substrate is put onto the first one. as the connection is tightened, interference effects disappear to indicate that optical contact has been achieved.

 

the article concluded, “the processes needed to prepare the mecsel (membrane external-cavity surface-emitting laser) devices, such as large-scale bonding of whole wafers to transparent substrates followed by removal of the original substrate, are common in industry and generally available for most semiconductor material systems.

 

“the flexibility in designing its active region, combined with the possibility of stacking several active-region membranes, creates a high level of adaptability for the mecsel. no doubt, existing gaps in the available wavelengths of high-quality semiconductor lasers will be further narrowed in coming years as the mecsel continues to evolve.”

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