Rare-earth Doped Semiconductors Research Articles

CMSE 2022 Preface

The proceedings provide a selection of thirty-eight peer-reviewed papers presented at the 11th Global Conference on Materials Science and Engineering (CMSE 2022), held as a virtual conference on September 16-19, 2022.By the tradition annually followed in the full decade of its history, CMSE 2022 was dedicated to various aspects of Materials Science and Engineering. Given the aggravated Covid situation, the conference format was fully converted to the online mode to ensure the safety of participants, abandoning the previously scheduled on-site preparation plans in Shenzhen, China.CMSE 2022 was conducted via Microsoft Teams. The full three days of the conference comprised namely keynote speeches, oral presentations, and poster presentations, each part followed by a Q&A discussion. Firstly, the conference audience containing over a hundred participants from 23 countries enjoyed the keynote speeches of three distinguished professors: Prof. Qixin Guo from Saga University, Japan, Prof. Yarub Al-Douri from the American University of Iraq, Iraq, and Prof. Rodrigo Martins from Universidade Nova de Lisboa, Portugal, who shared their deep insights on rare earth doped semiconductors, quinternary alloys’ multi-application, and green and low-cost printed electronics, respectively. Next, over eighty oral and poster presentations were delivered successfully with informative results from related materials science and engineering fields. More detail can be found in the online version of the conference program. The online format of the conference somewhat limited the informal discussion opportunities for its participants. However, despite Covid-induced restrictions, this conference fulfilled its ultimate goal of bringing together experts from universities, academic institutions, industrial companies, and so on, updating the state-of-the-art developments and challenges.The selected thirty-eight contributions cover the latest advances in innovative materials, materials technology and materials properties, microstructure, testing & characterization, processing, etc. They focus on theoretical and analytical methods, numerical simulations, and experimental techniques with regard to industrial applications. All papers passed a rigorous reviewing process by the International Committee experts, whose reviews and comments were crucial for enhancing the scientific merit and quality of the proceedings.List of Committee Members is available in this Pdf.

Preparation of rare-earth thulium doped tin-oxide thin films and their applications in thin film transistors

Tm3+ doped SnO2 semiconductor thin films were prepared by RF magnetron sputtering method. The doping effects of rare-earth thulium on the crystal structures, optical properties, chemical compositions, surface morphologies of tin-oxide thin films, together with the electrical properties of the corresponding SnTmO thin film transistors (TFTs), were investigated. SnTmO semiconductor thin films with polycrystalline structures feature a wide bandgap of over 3.8 eV. XPS results reveal the typical photoelectron signals of Sn4+ and Tm3+. Smaller crystallite size and more grain boundaries can be formed in doped SnO2 samples which may be responsible for the degradation of device mobility. It was found that the electrical properties of SnO2 TFTs can be modulated by Tm3+ incorporation. The appropriate Tm3+ doping concentration is around 1.6 at.% within our experimental conditions. The optimized field-effect mobility, subthreshold swing, threshold voltage, on-off current ratio and the interface trap density are 5.5 cm2 V−1 s−1, 0.618 Vdec−1, −2.3 V, 5 × 107 and 6.7 × 1011 cm−2, respectively. Stability measurements show threshold voltage shifts of 12.3 V and −11.7 V in PBS and NBS process respectively. This study may provide useful understandings on rare-earth doped SnO2 semiconductors.

One-step synthesis of Er3+-doped BiOI0.5Cl0.5 supported on Ni foam with enhanced photocatalytic degradation under visible light

A promising photocatalyst with favorable visible-light absorption and efficient charge separation is desirable for environmental protection. In this study, orderly nanosheets of binary bismuth oxyhalides (BiOI0.5Cl0.5) doped with the rare earth metal ion Er3+ were immobilized on Ni foam by a facile one-step solvothermal method. The photocatalytic performance of the obtained photocatalyst (Ni foam@Er-BiOI0.5Cl0.5) was investigated. The effects of Er3+-doping on BiOI0.5Cl0.5 and the photocatalyst loading amount on Ni foam were systematically studied. Ni foam, which is a self-standing conducting 3D skeleton, enhanced the efficiency of the separation of the photogenerated electrons and holes. The Er3+ doped in BiOI0.5Cl0.5 also accelerated the separation of the photogenerated electron-hole pairs by creating abundant oxygen vacancies and surface defects for electron trapping and pollutant adsorption. Consequently, Er3+ doping and immobilization on Ni foam synergistically enhanced the photocatalytic activity of Ni foam@Er-BiOI0.5Cl0.5. Photocatalytic degradation experiments of Acid Red1 were carried out, and the photocatalytic efficiency of Ni foam@Er-BiOI0.5Cl0.5 was found to be enhanced by 1.5 times compared to that of pure BiOI0.5Cl0.5. In addition, the photocatalyst could be easily recycled several times with good stability. Remarkably, the photocatalytic activity of BiOI0.5Cl0.5 is enhanced by effectively doping Er3+ into binary bismuth oxyhalides rather than synthesizing upconversion nanoparticles, and the directly doped Er3+ could react with photoexcited electrons to generate superoxide radicals. So we give a facile way to prepare a rare-earth doped semiconductor photocatalyst that is reusable, recyclable and highly efficient for photodegradation of organic dye from water.

Computational Study of Electronic Structure Rare-Earth Doped Semiconductor III-V: GGA Approximation

Electronic structure of rare-earth doped semiconductor III-V have been investigated. Based on density functional theory GGA Approximation, the electronic structure of AlN and GaN are calculated in wurtzite structure. The direct band gap of pristine AlN and GaN has slightly changed from experimental results. Rare-earth atoms substitute group III elements and bonded with four N atoms. The bond length of RE-N have changed 14.5% from Al-N bond length. Impurity energy 4f of rare-earth has found between the conduction band and valence band. By this, the 4f energy can explain the luminescence process from rare-earth atoms to host materials. The band structure is expected to allow optical transition in IR-UV emission range. Rare-earth doped semiconductor III-V has high potential to be applied to lower energy of light emitting diodes and energy-saving devices.

Rare earth doped semiconductor nanomaterials and its photocatalytic and antimicrobial activities

Investigations on dually active rare earth doped ZnO nanomaterials for enhanced photocatalytic and anti-microbial activity were conducted. Dy3+ doped ZnO was synthesised via a co-precipitation method. The dopant concentrations were varied from 3 to 10 wt% and characterised by XRD, FT-IR, UV–vis-DRS, PL, FE-SEM, EDAX, HR-TEM, AFM, BET, XPS and EPR techniques. The prepared material was found to be in the nano regime (38–47 nm) displaying hexagonal morphology. Surface roughness was also very high (47.49 nm) as confirmed by AFM. EPR confirmed that OH radicals were generated on light irradiation. The prepared photocatalysts were investigated for Visible and UV induced photocatalytic activities for the degradation of model pollutants like OrG and MG dye. The 10DZ nanomaterial displays 99.5% of degradation of OrG, similarly more than 94% of degradation of MG was observed under UV and Visible light irradiation. The degradation of OrG and MG was carried out for standard TiO2 under UV and Visible light irradiation and the results proves that 10DZ exhibits better photocatalytic activity than TiO2. The nanomaterial was screened for its anti-microbial activities against certain species of bacterial and fungal species. 10% doped nanomaterial was found to posses excellent photocatalytic activities both under Visible and UV light irradiation. The reaction followed a pseudofirst order kinetics. The activities were far higher than undoped ZnO. The anti-microbial activities were also higher than the standard controls which proves the prepared material to act dually both as a photocatalytic and anti-microbial agent.

Oxidation of organic dye using nanocrystalline rare earth metal ion doped CeO2 under UV and Visible light irradiations

Advanced Oxidation Process using semiconductor photocatalysts is an emerging technique to remove toxic organic molecules from aqueous phase. Design and development of newer photocatalytic systems are scarce in the literature. Hence, the present research focuses on rare earth doped semiconductor materials such as cerium doped dysprosium oxide was synthesized by co-precipitation method and characterised by XRD, FT-IR, UV-DRS, FESEM, EDAX analysis and HRTEM techniques. FESEM confirms that particles were spherical ranged from 23 to 31nm. EDAX confirmed the presence of Ce, Dy and O elements in the prepared photocatalysts. Photocatalytic efficiency of the prepared catalyst was evaluated in the degradation of a model organic dye such as Orange G dye under UV and Visible light irradiations. The photodegradation efficacy of the prepared material was evaluated by varying parameters like aqueous pH, catalyst dosage and dye concentration for photodegradation of the dye molecules. 15mg of photocatalyst showed excellent activity with 94% degradation under visible light and 10mg of photocatalyst showed better activity for 10ppm of OG dye with 96% for UV light irradiation under neutral pH. Kinetic studies obeys pseudo-first order reaction. The Chemical Oxygen Demand (COD) level decreases for both Visible and UV light irradiation. Effect of electrolytes such as NaCl, KCl, Na2CO3 and MgSO4 were investigated and the catalyst exhibited good activity in both UV and Visible light irradiations.

Substantial enhancement of red emission intensity by embedding Eu-doped GaN into a microcavity

We investigate resonantly excited photoluminescence from a Eu,O-codoped GaN layer embedded into a microcavity, consisting of an AlGaN/GaN distributed Bragg reflector and a Ag reflecting mirror. The microcavity is responsible for a 18.6-fold increase of the Eu emission intensity at ∼10K, and a 21-fold increase at room temperature. We systematically investigate the origin of this enhancement, and we conclude that it is due to the combination of several effects including, the lifetime shortening of the Eu emission, the strain-induced piezoelectric effect, and the increased extraction and excitation field efficiencies. This study paves the way for an alternative method to enhance the photoluminescence intensity in rare-earth doped semiconductor structures.

希土類添加半導体の精密制御成長と発光機能

希土類添加半導体の精密制御成長と発光機能

Induced magnetic moment of Eu3+ ions in GaN

Magnetic semiconductors with coupled magnetic and electronic properties are of high technological and fundamental importance. Rare-earth elements can be used to introduce magnetic moments associated with the uncompensated spin of 4f-electrons into the semiconductor hosts. The luminescence produced by rare-earth doped semiconductors also attracts considerable interest due to the possibility of electrical excitation of characteristic sharp emission lines from intra 4f-shell transitions. Recently, electroluminescence of Eu-doped GaN in current-injection mode was demonstrated in p-n junction diode structures grown by organometallic vapour phase epitaxy. Unlike most other trivalent rare-earth ions, Eu3+ ions possess no magnetic moment in the ground state. Here we report the detection of an induced magnetic moment of Eu3+ ions in GaN which is associated with the 7F2 final state of 5D0→7F2 optical transitions emitting at 622 nm. The prospect of controlling magnetic moments electrically or optically will lead to the development of novel magneto-optic devices.

How to describe concentration quenching in rare earth doped semiconductors

AbstractWe report on two approaches to describe concentration quenching of rare earth doped semiconductors. The examples used are terbium doped aluminium nitride and silicon carbide. The aim of the presented work is to introduce a frame of description that can be used to analyse experimental results. The first approach, a rate equation based model, uses mean values for both the transition probabilities and the centre interdistance.The second approach, an atomistic Monte‐Carlo simulation, is capable of describing single centres and thus can handle different spatial distributions of the centres. Both models describe the experimentally observed concentration quenching effects. The Monte‐Carlo simulation is more appropriate since it can handle microstructural influences like clustering or precipitation of the rare earth ions. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The Roles of Electrons and Holes in Luminescence of Rare-earth Doped Semiconductors

The roles of electrons and holes in photo-excited samarium doped titanium dioxide (TiO2:Sm) thin film were investigated with electric measurement techniques. For this purpose, a structural modification using interface states in silicon oxide between TiO2:Sm and a conductive silicon substrate was used. Since the interface states make a barrier to electrons in positive DC bias VDC, selective injection of holes into TiO2:Sm can be realized in VDC>0. Photo-excited dielectric relaxation (PEDR) technique, namely frequency dispersion measurement of complex impedance under excitation light, and the selective injection revealed that the Sm excitation was induced by an electron trapping with a slow response of ∼12 Hz and following recombination with holes in host TiO2 with ∼950 Hz.

Resonant photoemission of rare earth doped GaN thin films

The 4 d → 4 f Fano resonances for various rare earth doped GaN thin films (RE = Gd, Er, Yb) were investigated using synchrotron photoemission spectroscopy. The resonant photoemission Fano profiles show that the major Gd and Er rare earth 4 f weight is at about 5–6 eV below the valence band maximum, similar to the 4 f weights in the valence band of many other rare earth doped semiconductors. For Yb, there is very little resonant enhancement of the valence band of Yb doped GaN, consistent with a largely 4 f 14 occupancy.

Charge propagation dynamics at trapping centers that induce the luminescence of rare-earth dopants in wide-gap materials

For rare-earth doped semiconductors, charge propagation from semiconductors to rare-earths is essential for excitation of optically active dopants. However, the qualitative model that has been widely accepted to describe this process is based upon indirect evidence; in this model, it is believed that trapping and subsequent recombination of the charges at some rare-earth-related defect excite the dopants. In this work, we observe the sequential process directly, and quantify the trapped charge density and relaxation frequency using a photoelectric measurement technique for samarium-doped titanium dioxide with intense visible luminescence under ultraviolet light.

Growth and characterization of transition-metal and rare-earth doped III-nitride semiconductors for spintronics

ABSTRACTTransition metal (Cr) and rare-earth (Dd, Dy) doped III-nitride semiconductor bulk layers and superlattice (SL) structures are grown on sapphire (0001) substrates and GaN (0001) templates by plasma-assisted molecular-beam epitaxy. For the GaGdN/GaN and InGaGdN/GaN SL and Si co-doped samples, enhancement of magnetization and magnetic moment are observed, suggesting the carrier-mediated ferromagnetism. Low temperature growth of GaGdN can increase the Gd concentration and magnetization. Results for the Dy-doped GaN as well as the GaCrN/AlN/GaCrN tunnel magneto-resistance (TMR) diodes are also described.

An Amorphous Indium–Gallium–Zinc–Oxide Active Matrix Electroluminescent Pixel

In this study, an active matrix pixel was fabricated and characterized using indium gallium zinc oxide (IGZO) thin-film transistors and a novel electroluminescent (EL) Eu:IGZO thin-film phosphor. The results show that even large and unoptimized IGZO devices are capable of modulating at the frequencies necessary for modern display technology. Furthermore, we demonstrate a rare-earth doped amorphous-oxide semiconductor (AOS) EL phosphor that can be modulated via a TFT.

Two colour experiments in Eu3+ implanted GaN

Two colour experiments can be used to study the excitation mechanisms of rare-earth ions in rare-earth doped wide-bandgap semiconductors as well as the quenching of their photoluminescence (PL). The combined excitation of Eu3+ implanted GaN samples with a pulsed laser and a CW laser, corresponding, respectively, to a below bandgap excitation and to an above bandgap excitation, is investigated. A strong quenching of the rare-earth (RE) luminescence is observed with both lasers compared to the excitation with only one laser. The dependence of the Eu3+ 5D0 lifetime quenching with the emission wavelength and excitation density of the CW laser is presented. The results are explained within the frame of a model describing the occurrence of an Auger effect between excited Eu ions and free carriers created by the CW laser.

Co-Doping of Er-Doped SiC with Oxygen – A Promising Way Towards Efficient 1540 nm Emission at Room Temperature?

Rare-earth doped semiconductors like SiC provide potential use as light-emitting diodes or lasers. Of particular interest is erbium because of its intra 4/-shell transition at 1540 nm coinciding with the minimum absorption of optical fibers. However, the main problem is rather low intensities at room temperature. In this work, based on calculated spin-densities some of the Er-related EPR-spectra are assigned to Er-donor pairs within S=3/2 high spin states. In the light of a calculated excitation scheme, Er Si N C pairs are proposed to be responsible for the 1540 nm emission observed in n-type SiC. In comparison, the energy level for Er Si O C pairs is considerably lower. Since thermal quenching of the IR-emission is related to the position of the Er-level below the conduction band, co-doping of SiC: Er with oxygen would be very desirable, providing more intense emission at room temperature.

Intralayer and interlayer energy transfer from excitonic states into the Mn3d5shell in diluted magnetic semiconductor structures

We show that the Dexter-F\"orster-like radiationless resonance energy-transfer process from excitonic states into the Mn ${3d}^{5}$ shell in wide-gap (II,Mn)VI semiconductors is strongly enhanced if the total spin of the overall process is conserved. This requirement cannot be fulfilled in processes involving a bright exciton, i.e., other excitonic complexes or processes need to be involved. Of these we discuss dark excitons, donor-bound excitons ${D}^{0}X,$ negatively charged excitons ${X}^{\ensuremath{-}},$ and an Auger-like process. A careful analysis of the magnetic field and time dependence of the excitonic and Mn luminescence in the (Zn,Cd,Mn)Se samples under study gives evidence that the ${D}^{0}X$ complex plays a dominant role in the intralayer energy transfer. In asymmetric double quantum well (ADQW) structures consisting of a (Zn,Cd)Se well and a (Zn,Cd,Mn)Se well embedded in ZnSe barriers, there is a competition between the intralayer and interlayer energy-transfer processes from excitonic states into the Mn system. These interlayer processes take place between the Mn ions situated in the (Zn,Cd,Mn)Se well and spatially indirect excitons [where the hole is confined in the (Zn,Cd,Mn)Se and the electron confined in the (Zn,Cd)Se] as well as spatially direct excitons of the (Zn,Cd)Se well. The continuous magnetic-field tuning demonstrates convincingly the subtle interplay of excitonic band structure of the ADQW and spin effects in the energy-transfer processes. A spin-dependent energy transfer should be a general feature of rare-earth or transition-metal doped semiconductors such as II-VI or III-V semiconductors or even Er-doped Si or ${\mathrm{SiO}}_{2}.$

Quantum confinement in rare-earth doped semiconductor systems

Rare-earth doped materials are widely deployed in optoelectronics and optical telecommunications technology, despite the difficulties associated with doping silicon with optically active rare-earth ions. Nanotechnology promises new classes of materials and devices that exploit the unique optical and electronic properties of low-dimensional structures; in particular, quantum confinement can modify the electronic structure of semiconductor hosts in such a way as to greatly increase the radiative efficiency of the rare-earth dopant. This article reviews some of the recent developments in the field and highlights possible future directions.

Excitation cross section of erbium in semiconductor matrices under optical pumping

Based on a detailed consideration of excitation mechanisms of erbium in crystalline and amorphous matrix we present an analysis of the physical meaning of the Auger excitation cross section of Er{sup 3+} ions in semiconductor. It is demonstrated that large values of Auger excitation cross sections under optical pumping in semiconductor matrices are due to large values of band-to-band absorption coefficient exceeding by several orders of magnitude the absorption coefficient of erbium in dielectric SiO{sub 2} and Al{sub 2}O{sub 3} matrix. The Auger excitation cross section of Er{sup 3+} in semiconductor matrices is roughly given by the ratio of the matrix absorption coefficient to concentration of Er{sup 3+} ions. While the analysis of the excitation cross section is carried out for Er-doped crystalline and amorphous silicon, the results are expected to be applicable to the other rare-earth doped semiconductors. Based on low-temperature experimental results for crystalline silicon we get the Auger excitation coefficient of c{sub A}{sup cryst}{approx}7 x 10{sup -10} cm{sup 3}s{sup -1} and the effective excitation cross section {sigma}{sub eff}{sup cryst}=(2-8) x 10{sup -12} cm{sup 2}. For amorphous silicon at 100 K we obtain {sigma}{sub eff}{sup amorph}{approx}1.4 x 10{sup -14} cm{sup 2}.