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The VERTILAS breakthrough

Buried Tunnel Junction (BTJ) VCSEL

After the successful commercialization of short-wavelength VCSELs in the 1990’s, it took an unexpectedly long time until the first long-wavelength (>1.3 µm) VCSELs with reasonable performance were presented. The delay was due to challenges with regards to the different materials required for longer wavelengths. Among the various challenges), laser heating makes the realization of long-wavelength VCSELs the most difficult. The physical reason for the bad thermal behaviour is the poor thermal conductivity and increased thickness of long-wavelength DBRs as well as the stronger temperature dependence of the threshold current. The VERTILAS approach overcomes these problems by employing a high-reflective and thermally well-conducting hybrid metallic/dielectric mirror together with a buried tunnel junction (BTJ) to enable low-resistance lateral current confinement and waveguiding.

Draining the heat from the active region through the thin but highly reflective dielectric mirror into the integrated bottom gold heatsink yields an excellent cooling system.. The BTJ on the p-side of the active layer accomplishes the conversion of the confinement layers from p- to n+-type so that extremely low electrical series resistance between 20 and 50 Ω and only ultra-low Joule heating occurs. Additionally, the BTJ causes a transverse waveguiding that yields both a stable built-in transverse mode profile and small threshold currents.