Experimental and first-principles studies of high-pressure effects on the structural, electronic, and optical properties of semiconductors and lanthanide doped solids

Abstract

In this paper we present a broad overview of our recent experimental and theoretical results obtained for different types of materials: CdTe and CuGa1−xInxS2 chalcopyrite semiconductors, GaN/AlN wide band gap semiconductor quantum wells, and lanthanide-doped dielectric materials. The analysis of pressure-induced phase transitions, variations of the band gaps, refractive index and the pressure dependence of optical properties of these materials is discussed. The presented results show that the high pressure technique is a very useful tool for scientific research and development of of light-emitting technologies. It allows for identification of radiative recombination mechanisms in solid-state light emitters. In polar III–nitride semiconductors, ab initio calculations revealed that the pressure-induced change of the band gap plays minor role, whereas the built-in electric field in heterostructures increases with pressure thus affecting their basic physical properties, i.e., producing a large red-shift of the photoluminescence and lowering the quantum efficiency due to the quantum confined Stark effect. For wide (>4 nm) quantum wells, the reduction of the band-to-band emission efficiency leads to deep defect dominant emission which is almost pressure independent. The observed behavior proves that pressure investigations combined with ab initio calculations can identify the nature of the optical transitions and the main physical factors affecting the radiative efficiency in polar quantum well systems. Furthermore, high pressure studies of the emission and excitation spectra of Y2O2S doped with Tb3+ and Eu3+ allowed estimating the energies of the ground states of all divalent and trivalent lanthanide ions in respect to the valence and conduction band edges of the Y2O2S host. Band gap energy and difference between energies of the ground states of lanthanide ions and band edges have been calculated as a function of pressure. It is shown that pressure causes an increase of the energy of localized states related to the lanthanide ions with respect to the valence band, and an increase of the band gap energy.