Magneto-optic study of the interface in semimagnetic semiconductor heterostructures: Intrinsic effect and interface profile in CdTe-Cd1-xMnxTe

This paper is devoted to the description of the interface between a semimagnetic semiconductor (Cd1-xMnxTe) and a nonmagnetic one (CdTe), and to the study of its magnetic and magneto-optical properties, as revealed through the enhanced Zeeman splitting of carriers confined in heterostructures. The model (proposed earlier on phenomenological bases) takes into account both the chemical profile of the imperfect interface and the enhanced magnetism due to the reduced number of magnetic neighbors at the interface. We first justify the model (for low Mn contents) by considering the statistics of Mn clusters at the interface or in a single Cd1-xMnxTe monolayer embedded in CdTe. We also show that the sensitivity of the Zeeman effect to the presence of two-dimensional islands at the interface rapidly decreases as the island width increases; i.e., the measure is sensitive to the presence of isolated magnetic ions and not (or less) to roughness, and it characterizes the interface on the scale of interatomic distance. Then we apply this tool to a wide series of samples with different nominal characteristics and different growth conditions. A unique profile (determined with a single adjustable parameter) accounts for the enhanced Zeeman splitting observed on samples grown at low temperature (250-280 degrees C) under excess of Cd, independently of the details of the carrier-wave function and of its penetration into the magnetic barrier: this is a further (experimental) check of the calculation. The exponential profile deduced for these samples accounts for the larger enhancement of Zeeman splitting at the inverted interface (CdTe grown on Cd1-xMnxTe), compared to the normal interface (Cd1-xMnxTe on CdTe). It points to a complete exchange of Cd and Mn atoms between the two surface layers during growth (i.e., a segregation process with a segregation energy determined to be zero). We found very little influence of growth interruptions and of growing the Cd1-xMnxTe barrier under Te excess. As the growth temperature is raised above 300 degrees C, the interface further broadens, the additional broadening being identical for the two interfaces. Finally, we found that the Zeeman effect of carriers confined in quantum wells incorporating a magnetic inverted interface (including symmetrical quantum wells) is completely dominated by the effect of the nonabrupt profile, while a small contribution of the intrinsic effect seems to exist in a quantum well with only a normal magnetic interface or heterostructures with single Cd1-xMnxTe monolayers.