Growth and UV-A sensor applications of MgCdS/ZnCdS superlattices

The application of visible blind ultraviolet (UV)-A sensors was extensively studied for wide-bandgap II-VI compound epitaxial layers. The growth of ZnMgCdS quaternary alloys and MgCdS/ZnCdS short period superlattices were performed, and UV-A sensors were fabricated. The mole-fraction control of the ternary alloy would be much easier than that of the quaternary alloy, and various structures with certain bandgap energy can be designed. The cross-sectional TEM observation has revealed that well-defined superlattice structures could be achieved. Low-temperature photoluminescence (PL) exhibited that the intense and sharp luminescence peak was observed from superlattice samples compared with quaternary alloy layers having the similar bandgap energy. The PL peak position could be controlled by changing the layer thickness as well as the mole-fraction ratio of the alloy. The PL peak energy positions agreed well with theoretically predicted values. After the film growth, Au electrodes were evaporated and photo-sensitivity was characterized for metal-semiconductor-metal configurations. Sharp cut-off profiles were observed for samples, and its position was consistent with the PL peak position. The ON-OFF ratio of the device was similar to that of the device using the quaternary alloy layers.