Papers by Keyword: II-VI Compounds

Abstract: Wide band gap semiconductors, mainly GaN, have experienced much attention due to their application in photonic devices and high-power or high-temperature electronic devices. Especially the synthesis of InxGa1-xN alloys has been studied extensively because of their use in LEDs and laser diodes. Here, In is added during the growth process and devices are already very successful on a commercial scale. Indium in nitride ternary and quaternary alloys plays a special role; however, the mechanisms leading to more efficient light emission in In-containing nitrides are still under debate. Therefore, the behaviour of In in GaN and AlN, the nitride semiconductor with the largest bandgap is an important field of study. In is also an important impurity in another wide band gap semiconductor – the II-VI compound ZnO where it acts as an n-type dopant. In this context the perturbed angular correlation technique using implantation of the probe ¹¹¹In is a unique tool to study the immediate lattice environment of In in the wurtzite lattice of these wide band gap semiconductors. For the production of GaN and ZnO based electronic circuits one would normally apply the ion implantation technique, which is the most widely used method for selective area doping of semiconductors like Si and GaAs. However, this technique suffers from the fact that it invariably produces severe lattice damage in the implanted region, which in nitride semiconductors has been found to be very difficult to recover by annealing. The perturbed angular correlation technique is employed to monitor the damage recovery around implanted atoms and the properties of hitherto known impurity – defect complexes will be described and compared to proposed structure models.

Abstract: Single ZnO nanorods with diameters of 100nm were directly grown on GaN surface by using low-temperature hydrothermal synthesis. Individual nanorods were removed from the substrate and placed between the Au contact pads and the current voltage measurement was proceeded to characterize the electrical properties of the ZnO nanorods. By using thermionic field emission model of Padovani and Stratton , the resistivity, carrier concentration, electron mobility can be extracted with the values of 0.14 Ωcm, 9.2x1016/cm3,33.82cm2V-1s-1, respectively. The single ZnO nanorods also showed high sensitivity to the UV light (325nm). Under the UV illumination, the UV induced current increase nearly 10 times than the dark current. In addition, the nanorods also exhibited a slow UV response due to the effects of the oxygen ions on the surface of the nanorods.

Abstract: The bulk crystal growth of II-VI compounds, such as HgCdTe, CdZnTe etc., is usually carried out by Bridgman and modified Bridgman methods. Optimizing the growth process relies mainly on the understanding of the fundamental problems of solute and thermal transportation principles, which determines the composition segregations and other defects, including point defects, dislocations, precipitates, stacking faults, etc. In the last few years, the present author studied the coupling effects of the convection, thermal and solute transportation phenomena during the growth processes through both theoretical modeling and experimental methods. Several important phenomena, such as effects of ACRT forced convection on the thermal and solute field and the growth interface morphology, the shift of the growth interface due to the solute redistributions, solute segregation behaviors during the growth process, etc, are discussed. Based on these researches, technologies for growing high quality CdZnTe and other II-VI compounds have been developed.