Electronic properties of III-V semiconductor alloys are examined using first principles with the focus on the spatial localization of electronic states. We compare localization at the band edges due to various isovalent impurities in a host GaAs including its impact on the photoluminescence line widths and carrier mobilities. The extremity of localization at the band edges is correlated with the ability of individual elements to change the band gap and the relative band alignment. Additionally, the formation energies of substitutional defects are calculated and linked to challenges associated with the growth and formability of alloys. A spectrallyresolved inverse participation ratio is used to map localization in prospective GaAs-based materials alloyed with B, N, In, Sb, and Bi for 1.55 µm wavelength telecommunication lasers. This analysis is complemented by a band unfolding of the electronic structure and discussion of implications of localization on the optical gain and Auger losses. Correspondence with experimental data on broadening of the photoluminescence spectrum and charge carrier mobilities show that the localization characteristics can serve as a guideline for engineering of semiconductor alloys.

The recent progress in formation of two-dimensional (2D) GaN by a migration-enhanced encapsulated technique opens up new possibilities for group III-V 2D semiconductors with a band gap within the visible energy spectrum. Using first-principles calculations we explored alloying of 2D-GaN to achieve an optically active material with a tuneable band gap. The effect of isoelectronic III-V substitutional elements on the band gaps, band offsets, and spatial electron localization is studied. In addition to optoelectronic properties, the formability of alloys is evaluated using impurity formation energies. A dilute highly-mismatched solid solution 2D-GaN$_{1-x}$P$_x$ features an efficient band gap reduction in combination with a moderate energy penalty associated with incorporation of phosphorous in 2D-GaN, which is substantially lower than in the case of the bulk GaN. The group-V alloying elements also introduce significant disorder and localization at the valence band edge that facilitates direct band gap optical transitions thus implying the feasibility of using III-V alloys of 2D-GaN in light-emitting devices.Comment: 14 pages, 4 figures, 1 tabl

Density functional theory predicts an abrupt drop in the stability, in the kinetic barrier for polarization reversal and spontaneous polarization of a ScxAl1−xN wurtzite phase, when the Sc:Al ratio approaches 50:50. The same effect is obtained by the application of a tensile strain. The resulting polarization reversal barrier correlates with experimental coercive fields, and highly textured film measurements exhibit polarization values close to the theoretically predicted ones. Film thickness below 5 nm has a significant impact on the elastic properties.

Good control of the doping concentration and profile in the active layer of a transistor is paramount to achieve optimal device reliability and electrical performance. For nonconventional semiconductors such as InGaZnO 4 (IGZO), the doping mechanisms and the factors impacting them need to be rediscovered to achieve this control. In IGZO, an important doping mechanism is the formation of oxygen defects. In this work, we map the stability of oxygen defects in IGZO as a function of the defect concentration for three different phases: amorphous, C-axis aligned, and spinel IGZO. By means of a detailed analysis of the evolution of the metal coordination in the three phases, we rationalize the observed similarities and differences. This insight enables us to estimate the doping concentration caused by oxygen scavenging by different contact metals, liner materials, and hydrogen sources introduced during the integration of the material in a transistor flow. From a study of the contact resistance in the Ohmic, high carrier density contact regime, we obtain a lower bound to the contact resistance. We learn that the different carrier concentrations, caused by the variations in oxygen scavenging between contact metals, have a larger impact than the direct difference in contact resistance caused by the intrinsic electronic properties of metals.