Strain Effect On The Semiconductor Doping And The Oxide Interface Properties

Strain is not only existed in a variety of materials, but also has been used to engineer and enhance numerous properties of materials. Using the first-principles calculations within the density functional theory, we have studied that the formation energy and the diffusion barriers of interstitial Mn in GaAs with influence of external strain. We explored the effect of epitaxial strain on transport properties of the LaAlO3/SrTiO3interface. There are three parts in our researches of this paper.1) The strain effect in semiconductor was quite often described by the continuum elastic model, whose validity is still under debate. Based on the quantum mechanical analysis, we show that if the strain changes the electron occupation of the energy levels, the continuum elastic model would fail. Our finding is demonstrated by the first-principles calculation of Mn-doped GaAs. We also predict that under compressive strain will increase the substitutional Mn concentration, thus the Curie temperature TC, can be increased in Mn-doped spintronic materials.2) The influence of external strain on the diffusion barriers of interstitial Mn in GaAs is studied using the firstrst-principles calculations within the density functional theory. The diffusion barrier changes with strain in different manners: linear on the tensile strain and non-linear on compressive strain, in contrast to the linear behavior of the continuum elastic model. The discrepancy between the continuum elastic model and the results of the first-principles calculations, is attributed to the energy-level crossing caused by strain. Moreover, we found that the external strain can not only effectively change the diffusion barrier (even to zero, at certain strain), but also the position of saddle points along the migration path. Our finding provides an alternative way to reduce the population of interstitial Mn in GaAs, thus correspondingly to increase the Curie temperature of this system. 3) Using the first-principles calculations within the density functional theory, we have studied the effect of epitaxial strain on transport properties of the LaAlO3/SrTiO3interface. We calculated the formation energy of the oxygen vacancy in the polarized LaAlO3overlayer for np-type, n-type and p-tupe interface at the oxygen-rich (O2) growth. We have also found that the formation energy of the oxygen vacancy increases with compressive strain.