GaInNAsSb alloys enable the realization of long-wavelength lasers on GaAs substrates. Despite challenges in material growth relatively low threshold 1.55 μm edge-emitting lasers have been demonstrated. These lasers employ tensile-strained GaNAs barriers to compensate the high compressive strain of the GaInNAsSb quantum well (QW). This is indispensable to avoid degradation of the optical quality of the QW. Unfortunately, the small conduction and valence band offsets between GaInNAsSb and GaNAs allow the carriers to escape thermoinically from the QW into the barriers, where they recombine non-radiatively due to the poor optical quality of GaNAs. These processes result in higher thresholds and a degradation of the temperature sensitivity (T<sub>0</sub>) of the lasers. Therefore, to improve the performance of the lasers it is necessary to optimize the thickness of the GaNAs barriers or alternatively use GaAsP layers, which are also tensile strained on GaAs, to compensate the strain in the quantum well. In this work, we investigate the effects of barrier and well thicknesses on the luminescence efficiency of GaInNAsSb/GaNAs quantum wells and present the growth and characterization of GaInNAsSb quantum wells with GaAsP strain compensating layers.
The quantum well structures were grown by molecular beam epitaxy and consist of a 300 nm GaAs buffer layer, a GaInNAsSb QW surrounded by either GaNAs or GaAs/GaAsP barriers, and a 50 nm GaAs cap layer. Photoluminescence (PL) measurements of GaInNAsSb SQWs with different GaNAs barrier thickness indicate that the optical quality of the QW degrades considerably if the strain in the well is not fully compensated by the strain in the barriers. On the other hand, over compensation of the strain does not result in a significant improvement of the luminescence efficiency as confirmed by PL measurements of QWs with different well thicknesses.
To investigate the use of GaAsP strain compensating layers GaInNAsSb QWs were surrounded by a 10 nm GaAs spacer and a 20 nm GaAsP layer. The nominal P concentration in the GaAsP layer was 20%, which yields approximately the same strain as the GaNAs barriers. The structural quality of the QW is excellent as indicated by the Pendellosung fringes in the x-ray diffraction (XRD) scans. The PL intensity of the sample was lower than the structure with GaNAs barriers, which can be attributed, at least in part, to the reduced injection efficiency of the structure with GaAs-GaAsP barriers. The peak PL wavelength was blueshifted by ~50 nm compared to the structure with GaNAs barriers. It is thus necessary to increase the In and/ or N concentration in the QW to achieve emission at 1550 nm.