Investigation on (Al0.7Ga0.3)0.5In0.5P∕(Al0.3Ga0.7)0.5In0.5P multi-quantum-barrier superlattice using cross-sectional scanning tunneling microscopy

Abstract

Cross-sectional scanning tunneling microscopy (XSTM) is used to study a multi-quantum-barrier (MQB) structure consisting of (Al0.7Ga0.3)0.5In0.5P∕(Al0.3Ga0.7)0.5In0.5P semiconductor superlattice for use in AlGaInP laser devices. Quantitative analysis of the MQB was made difficult by poor image contrast due to the intrinsic small band offset of 80meV between adjacent layers in the large band-gap semiconductor superlattices. This is in addition to the presence of cleavage-induced monatomic steps at the clean cleaved (110) surface as they effectively mask the weak electronic features of the superlattice. To overcome these problems, the image contrast was enhanced by the choice of tunneling conditions, in particular, reducing the tip-sample separation and the origin of this mechanism is believed to be associated with tip-induced band bending. In addition, the use of arithmetic manipulation of images to eliminate physical features such as step defects on the cleaved surface is also reported. This allowed quantitative analysis to be performed on the superlattice. Results from the XSTM studies showed that the (Al0.7Ga0.3)0.5In0.5P∕(Al0.3Ga0.7)0.5In0.5P superlattices have very limited interdiffusion. This is in stark contrast to other MQB candidates involving Al0.5In0.5P∕Ga0.5In0.5P and Al0.5In0.5P∕(Al0.3Ga0.7)0.5In0.5P superlattices which revealed extensive broadening of the well in the superlattices as previously studied by the authors.