|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||V6, Resonant Periodic Gain InAs Quantum Dot VECSEL
||Alexander R Albrecht, Christopher P Hains, Thomas J Rotter, Andreas Stintz, Kevin J Malloy, Ganesh Balakrishnan
|On-Site Speaker (Planned)
||Alexander R Albrecht
Edge-emitting semiconductor lasers based on MBE-grown, self-assembled InAs quantum dot (QD)
active regions emitting around 1300 nm have demonstrated excellent device performance, including low sensitivity to operating temperature and record-low thresholds. The application of QDs in vertical-cavity lasers requires the stacking of several QD layers to achieve sufficient gain for lasing. The resulting accumulation of strain can affect material quality and degrade device performance.
In this investigation we compared two different arrangements of the QD active regions in a vertical-external-cavity surface-emitting laser (VECSEL) structure, both utilizing a total of 12 InAs QD layers, each embedded inside an InGaAs quantum well. The first, a more traditional VECSEL design consists of groups of 3 closely spaced QD layers placed at 4 adjacent antinodes of the optical standing wave. The second structure employs a purely resonant periodic gain (RPG) structure, with each of the 12 QD layers placed at a separate electrical field antinode. This design allows for greater spacing between the InAs layers, greatly reducing the negative effects of strain accumulation.
The devices were mounted to a thermo-electrically cooled stage using thermal grease. A fiber-coupled 808 nm diode laser was used as pump source, focused to a 300 μm diameter spot on the semiconductor surface. A 1% transmission output coupler with 25 cm radius of curvature completed the VECSEL cavity. CW operation was achieved with thermally limited output powers of 400 mW for the RPG structure, compared to only 100 mW for the traditional design. Making use of the growth non-uniformity across the 3 inch GaAs substrate, the operating wavelength could be tuned from 1220 nm to 1280 nm.
A portion of the RPG sample was thinned by mechanical polishing to 100 μm and the chip was bonded with indium to a thermal grade polycrystalline CVD diamond heat spreader of 300 μm thickness. The resulting assembly was clamped in a water cooled copper heat sink maintained at a temperature of 20°C. This greatly increased the usable pump power before thermal rollover, resulting in 2.5 W of cw output power, the first reported multi-Watt level QD VECSEL around 1250 nm.