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Output power enhancement of 100% for quaternary GaInAsSb/AlGaAsSb semiconductor disc lasers grown with a sequential growth scheme
Molecular beam epitaxial (MBE) growth and lasing operation of quaternary GaInAsSb/AlGaAsSb-based optically-pumped vertical-external-cavity surface-emitting lasers (VECSEL) emitting at a wavelength of 2.0 ?m are reported. MBE growth of such structures is particularly challenging as it requires, apart from the large total thickness of the epitaxial layer stack of 10S12 ?m a change of group-III fluxes for the growth of AlAsSb and low Al-content AlGaAsSb. Two different growth schemes are compared. The first one is the conventional growth procedure in which the wafer remains in the growth chamber and the growth is interrupted at the interfaces before and after the active region to adjust the group-III cell temperatures for different flux settings. At the interfaces where the growth had to be interrupted, secondary-ion mass-spectrometry revealed the unintentional incorporation of In at a concentration equivalent to 1S2 monolayers. Here we introduce a new growth procedureLthesequential growth scheme where each section of the VECSEL is grown separately, and after the growth of a section, the sample is taken out of the growth chamber and stored in the buffer chamber while the group-III cell temperatures are adjusted. After the new group-III fluxes have been stabilized, the wafer is transferred back into the growth chamber and the next section of the laser is grown. This way the unintentional incorporation of In at interfaces between different sections of the VECSEL structure can be avoided. A comparison of nominally identical VECSEL structures grown within the same growth campaign using the two different growth procedures reveals an increase of the maximum output power of nearly 100% for a 2.0 ?m emitting VECSEL structure grown with the sequential growth scheme accompanied by an improvement of the optical-to-optical power conversion efficiency from 14.4% to 21.5%.