Electronic structure of ScN determined using optical spectroscopy, photoemission, and ab initio calculations (original) (raw)
Related papers
Applied Physics Letters
Scandium nitride (ScN) has recently attracted much attention for its potential applications in thermoelectric energy conversion, as a semiconductor in epitaxial metal/semiconductor superlattices, as a substrate for GaN growth, and alloying it with AlN for 5G technology. This study was undertaken to better understand its stoichiometry and electronic structure. ScN (100) single crystals 2 mm thick were grown on a single crystal tungsten (100) substrate by a physical vapor transport method over a temperature range of 1900–2000 °C and a pressure of 20 Torr. The core level spectra of Sc 2 p3/2,1/2 and N 1 s were obtained by x-ray photoelectron spectroscopy (XPS). The XPS core levels were shifted by 1.1 eV toward higher values as the [Sc]:[N] ratio varied from 1.4 at 1900 °C to ∼1.0 at 2000 °C due to the higher binding energies in stoichiometric ScN. Angle-resolved photoemission spectroscopy measurements confirmed that ScN has an indirect bandgap of ∼1.2 eV.
Development of semiconducting ScN
Physical Review Materials, 2019
Since the 1960s advances in electronic and optoelectronic device technologies have been primarily orchestrated by III-V semiconductors, which have led to an age of consumer electronic devices with unprecedented social and economic impacts. Group III-V semiconductors such as GaAs, GaN, InAs, and GaP and their solid solution alloys are not only the building blocks of modern solid-state lighting, photodetectors, sensors, and high-speed power-electronic and optoelectronic devices, they have also been actively researched and developed for over six decades to understand and innovate fundamental materials science, physics, and device engineering properties. Yet there is a widespread realization today that contemporary grand challenges of our society such as energy efficient electronics and computing, secure information processing, energy security, imaging, sensing, etc., require more advanced materials and better device integration technologies. At the same time, several important device technologies of the modern era such as thermoelectricity that converts waste heat into electrical energy, plasmonic materials, and devices that could be utilized to harvest optical energy in solar photovoltaics, solar thermophotovoltaics, photocatalysis, etc., also require materials and heterostructure metamaterials that are not possible to achieve with traditional III-V semiconductors. Scandium nitride (ScN) is a group 3 rocksalt nitride semiconductor, which can overcome some of the limitations of traditional III-V semiconductors, and could lead to novel device functionalities. However, unlike other well-known III-V semiconductors, very little attention has been devoted to understand and engineer ScN's physical properties until very recently. In this research update, we detail the progress that has taken place over the last several years to overcome the materials engineering challenges for high-quality epitaxial ScN thin-film growth, analysis of its physical properties, and epitaxial integration of ScN with other rocksalt metallic nitrides. Along with the attractive physical properties common to most transition-metal nitrides such as high hardness, large melting temperature, and chemical, thermal, and morphological stability, ScN also exhibits rocksalt crystal structure with octahedral bonding coordination, indirect band gap, preferential n-type and p-type doping, and the ability to epitaxially integrate with other metallic materials (such as TiN, ZrN, HfN, etc.) to deposit single-crystalline epitaxial metal/semiconductor multilayers and superlattices without the presence of extended defects. All of these advances could lead to ScN based materials and devices with improved efficiencies and industrial applications.
Compensation of native donor doping in ScN: Carrier concentration control and p-type ScN
Applied Physics Letters
Scandium nitride (ScN) is an emerging indirect bandgap rocksalt semiconductor that has attracted significant attention in recent years for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices and as a substrate material for high quality GaN growth. Due to the presence of oxygen impurities and native defects such as nitrogen vacancies, sputter-deposited ScN thin-films are highly degenerate n-type semiconductors with carrier concentrations in the (1-6) Â 10 20 cm À3 range. In this letter, we show that magnesium nitride (Mg x N y) acts as an efficient hole dopant in ScN and reduces the n-type carrier concentration, turning ScN into a p-type semiconductor at high doping levels. Employing a combination of high-resolution X-ray diffraction, transmission electron microscopy, and room temperature optical and temperature dependent electrical measurements, we demonstrate that p-type Sc 1-x Mg x N thin-film alloys (a) are substitutional solid solutions without Mg x N y precipitation, phase segregation, or secondary phase formation within the studied compositional region, (b) exhibit a maximum hole-concentration of 2.2 Â 10 20 cm À3 and a hole mobility of 21 cm 2 /Vs, (c) do not show any defect states inside the direct gap of ScN, thus retaining their basic electronic structure, and (d) exhibit alloy scattering dominating hole conduction at high temperatures. These results demonstrate Mg x N y doped p-type ScN and compare well with our previous reports on p-type ScN with manganese nitride (Mn x N y) doping.
Physical Review B, 2004
ScN͑001͒ 1 ϫ 1 surfaces have been prepared by growing ScN on MgO͑001͒ using radio frequency molecular beam epitaxy. In situ ultrahigh vacuum scanning tunneling spectroscopy indicates that the Fermi level at the surface lies slightly above the Sc 3d conduction band edge, which is attributed to a downward band bending at the surface. In situ scanning tunneling microscopy is used to image the Sc and N atom sublattices. While only one atom ͑Sc͒ appears at small negative bias, both atoms (Sc and N) appear at certain positive sample biases due to the partially ionic nature of the bonding. Charge accumulation near ionized subsurface donors is evident from the long-range topographic distortions at the surface. The combination of tunneling spectroscopy and optical absorption results show that ScN has an indirect bandgap of 0.9± 0.1 eV and a direct transition at 2.15 eV.
A comparative study for structural and electronic properties of single-crystal ScN
Condensed Matter Physics, 2011
A comparative study by FP-LAPW calculations based on DFT within LDA, PBE-GGA, EVex-PWco-GGA, and EVex-GGA-LDAco schemes is introduced for the structural and electronic properties of ScN in RS, ZB, WZ, and CsCl phases. According to all approximations used in this work, the RS phase is the stable ground state structure and makes a transition to CsCl phase at high transition pressure. While PBE-GGA and EVex-PWco-GGA's have provided better structural features such as equilibrium lattice constant and bulk modulus, only EVex-PWco-GGA and EVex-GGA-LDAco's have given the non zero, positive indirect energy gap for RS-ScN, comparable with the experimental ones. The indirect band gap of ScN in RS phase is enlarged to the corresponding measured value by EVex-PWco-GGA+U SIC calculations in which the Coulomb self and exchangecorrelation interactions of the localized d-orbitals of Sc have been corrected by the potential parameter of U. The EVex-PWco-GGA calculations have also provided good results for the structural and electronic features of ScN in ZB, WZ, and CsCl phases comparable with the theoretical data available in the literature. EVex-PWco-GGA and EVex-PWco-GGA+U SIC schemes are considered to be the best ones among the others when the structural and electronic features of ScN are aimed to be calculated by the same exchange-correlation energy approximations.
Stability and magnetic properties of Mn-substituted ScN semiconductor from first principles
Computational Materials Science, 2008
We present a spin density functional theory (DFT) study for semiconducting ScN and Mnsubstituted ScN. Their structural and magnetic properties have been investigated using the all electrons augmented spherical wave method (ASW) with a generalized gradient GGA functional for treating the effects of exchange and correlation. Band structure calculations show that ScN is semiconductor with a narrow indirect band gap Γ-X of 0.54 eV. The total-energy versus volume calculations show that ternary Sc 0.75 Mn 0.25 N nitride is more stable in face centered tetragonalrocksalt (fct-rocksalt) structure, found experimentally, than the cubic rocksalt one. Spin polarized results, at theoretical equilibrium, indicate that the ground state of Sc 0.75 Mn 0.25 N is ferromagnetic with a high moment at Mn-atom (3.44µ B), and zero moment on Sc and N ones. The magnetovolume effects of Mn-substitution in ScN lattice are discussed. The electronic structures analyzed from site/spin projected density of states and chemical bonding, for both the mononitride and the ternary alloy, are reported. A discussion of the structural and magnetic properties of Sc 0.75 Mn 0.25 N is given with a comparison to ScN, in order to get insights of the Mn-substitution effects.
Synthesis and study of ScN thin films
2021
Susmita Chowdhury, Rachana Gupta, Parasmani Rajput, Akhil Tayal, Dheemahi Rao, 5, 6 Reddy Sekhar, Shashi Prakash, Ramaseshan Rajagopalan, S. N. Jha, Bivas Saha, 5, 6 and Mukul Gupta ∗ Applied Science Department, Institute of Engineering and Technology, DAVV, Indore, 452017, India Beamline Development and Application Section, Physics Group, Bhabha Atomic Research Centre, Mumbai 400085, India Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22607 Hamburg, Germany Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064,India International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research,Bengaluru 560064, India School of Advanced Materials (SAMat), Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru 560064,India Surface and Nanoscience Division, Materials Science Group, Indira Gandhi Centre for Atomic Research, HBNI, Kalpakkam 603102, India UGC-DAE Consortium for Sc...
Positron Structural Analysis of ScN Films Deposited on MgO Substrate
Acta Physica Polonica A
Scandium nitride (ScN) is a semiconductor with a rocksalt-structure that has attracted attention for its potential applications in thermoelectric energy conversion devices, as a semiconducting component in epitaxial metal/semiconductor superlattices. Two ScN films of 118 nm and 950 nm thicknesses were deposited at the same conditions on MgO (001) substrate by reactive magnetron sputtering. Poly-orientation of films was observed with first an epitaxial growth on MgO and then a change in the orientation growth due to the decrease of the adatom mobility during the film growth. Positron lifetime measurements showed a high concentration of nitrogen vacancies in both films with a slightly higher concentration for the thicker ScN film. Presence of nitrogen vacancies explains the values of direct band gaps of 2.53±0.01 eV, and 2.56±0.01 eV which has been measured on ScN films of 118 nm and 950 nm thicknesses, respectively.
Molecular beam epitaxy control of the structural, optical, and electronic properties of ScN(001)
Journal of Applied Physics, 2001
Scandium nitride ͑001͒ oriented layers have been grown on magnesium oxide ͑001͒ substrates by molecular beam epitaxy using a rf-plasma source and a scandium effusion cell. The Sc/N flux ratio is found to be critical in determining the structural, optical, and electronic properties of the grown epitaxial layers. A distinct transition occurs at the point where the Sc/N flux ratio equals 1, which defines the line between N-rich and Sc-rich growth. Under N-rich conditions, the growth is epitaxial, and the surface morphology is characterized by a densely packed array of square-shaped plateaus and four-faced pyramids with the terraces between steps being atomically smooth. The films are stoichiometric and transparent with a direct optical transition at 2.15 eV. Under Sc-rich conditions, the growth is also epitaxial, but the morphology is dominated by spiral growth mounds. The morphology change is consistent with increased surface diffusion due to a Sc-rich surface. Excess Sc leads to understoichiometric layers with N vacancies which act as donors. The increased carrier density results in an optical reflection edge at 1 eV, absorption below the 2.15 eV band gap, and a drop in electrical resistivity.
Theoretical study on the possibility of bipolar doping of ScN
2008
Scandium nitride (ScN) is a semiconducting transition metal nitride for which there are not identified dopants. We present local density functional calculations, in supercell approach, for ScN doped with O and C in N-sites and Ca and Ti in Sc-sites. Small additions of these atoms have the effect of shifting the Fermi level within the electronic band structure. O and