Interface Control And Electronic Properties For AlGaN Superlattices

As the third-generation semiconductors, GaN, Al N and their solid solution play a significant role in the violet spectra and devices with high power, high frequency and high temperature. Besides, for superlattices, the electronic property could be controlled by adjusting the ration of barriers and wells layer thickness, defects or doping, which have a broad of prospect of application in the new semiconductor optoelectronic devices. Therefore, based on the first principle with the Density Function Theory(DFT), this paper aims at discussing the bandgap by the ration of barriers and wells layer thickness and the effect of vacancies and dopants. These topics as follows:First of all, it is mainly to discuss bandgap in the ideal superlattice. The results show that both in the wurtizte structures and zinc-blende structures, the bandgap manifest the same trend which decreases first and then increases with the increase of barrier thickness. When the thickness of well layers is equal to that of barrier layers, its bandgap reaches a minimum. Finally, the style of GaN/AlN superlattice with wurtzite structure changes from type I to type II.Secondly, it is mainly to discuss the effect of vacancies. The results show that nitrogen vacancies are major defects in both wurtzite and zinc-blende structure. For wurtzite structure, cation vacancies easily form at the interface B(a type-B interface is the plane between the last N layer in the GaN well and the adjacent first Al layer in the AlN barrier), and for anion vacancies easily form in the wells.Finally, it is mainly to discuss the effect of the impurities such as Mg-atom and Siatom. The results show that both for wurtzite and zinc-blende structure, the formation energy of Si-doping is lower than that of Mg-doping, which manifest Si-impurity is easily introduced into structures, and impurities are easily introduced into the wells GaN.