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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 μm 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 10–12 μm 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 1–2 monolayers. Here we introduce a new growth procedure—the sequential 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 μm 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%.

Molecular beam epitaxial growth and operation of quaternary GaInAsSb/AlGaAsSb-based optically pumped vertical-external-cavity surface-emitting lasers (VECSEL) emitting at wavelengths 2.X mu m are reported here. The epitaxial layer sequence of a VECSEL consists of three different sections: a distributed Bragg reflector (DBR), an active region, and a window layer terminated by a capping layer. The Al content of the AlGaAsSb layers Varies between 100% in the DBR and 30% in the barriers separating the compressively Strained GaInAsSb quantum wells (QW) in the active region. While the active region was grown without growth interruption, growth had to be interrupted at the interfaces between the above-mentioned sections to adjust the group-HI cell temperatures for different flux settings. At the growth interruption interfaces secondary-ion mass-spectrometry revealed the unintentional incorporation of In at a concentration equivalent to 1-2 monolayers. Inspire of the formation of InAsSb-like interfacial layers between the DBR and the active region on the one hand, and the active region and the window layer on the other, high-performance VECSELs emitting in the 2.0-2.3 mu m wavelength range have been grown. A maximum output power of 3.4 W at 2.25 mu m and -10 degrees C heat-sink temperature has been achieved with a maximum optical-to-optical power conversion efficiency of 24%.