Effect of indium in Al_0.65Ga_0.35N/Al_0.8Ga_0.2N MQWs for the development of deep-UV laser structures in the form of graded-index separate confinement heterostructure (GRINSCH)

AlGaN-based graded-index-separate-confinement-heterostructures (GRINSCHs) with Al_0.65Ga_0.35N/Al_0.8Ga_0.2N MQWs in their active region were grown by plasma-assisted MBE on (0001) 6H-SiC substrates. The MQWs were grown under excess Ga. Indium flux was used in addition in some of the samples in order to study the role of indium on the growth mode of such MQWs. Transmission electron microscopy (TEM) provides evidence that the bottom compositionally graded AlGaN layer in the GRINSCH structure may also be serving as a strain transition buffer layer, by blocking threading defects in the vicinity of the AlN/AlGaN heterointerface. X-ray diffraction (XRD) indicates that the interfaces in the MQWs grown in the presence of indium are sharper. However, photoluminescence (PL) studies indicate evidence of stimulated emission at relatively low threshold only in the sample grown without indium, which is attributed to deep band structure potential fluctuations in this sample. The presence of indium during growth led to more homogeneous AlGaN MQWs, which require higher excitation flux to produce population inversion.