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.

Density Functional Characterization of the 4f‐Relevant Electronic Transitions of Lanthanide‐Doped Lu2O3 Luminescence Materials

“…The energy difference between the Ln 2+ ground‐state band and VBM determining that the activator is an electron acceptor, and the difference between the Ln 3+ ground‐state energy and CBM confirming that the lanthanide center is an electron donor. Therefore, according to previous publications,, the above four groups of lanthanide impurity levels corresponds to four types of the electronic transition modes, which were illustrated in Figure b.…”

High pressure studies of radiative recombination processes in nitride semiconductor alloys and quantum structures

“…The presence of optically active defect states in these samples has been discussed in the Ref. 48. These factors can be verified using high-pressure technique, by comparing PL peak pressure coefficient as a function of MQWs widths determined experimentally, and obtained using DFT calculations.…”

“…42,43) Among other methods that can be used to investigate the piezoelectric effects, the high-pressure spectroscopy plays an important role, as it enables the determination of important parameters which are in many cases unavailable or difficult to obtain in another way. [44][45][46][47][48] For many years the main effort in the field of ternary nitride semiconducting materials has been focused on InGaN and AlGaN. Much less attention has been paid to the AlInN alloy.…”

Hydrostatic Pressure as a Tool for the Study of Semiconductor Properties – an Example of III-V Nitrides

“…In addition to strain and electric field, lattice mismatch leads to the generation of structural defects and can alter the incorporation of impurities, which affects the emission from the QWs [90]. As it was mentioned before, hydrostatic pressure spectroscopy allows the distinction of band-to-band radiative transitions and those involving deep or shallow defect states [90,[92][93][94][95][96][97]. Band-to-band transitions, or transitions from a shallow donor to the valence band state, occur when the pressure shift of PL is similar to that of the band gap.…”