ScGaN and ScAlN: emerging nitride materials (original) (raw)
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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.
ScGaN alloy growth by molecular beam epitaxy: Evidence for a metastable layered hexagonal phase
Physical Review B, 2004
Alloy formation in ScGaN is explored using rf molecular beam epitaxy over the Sc fraction range x = 0-100%. Optical and structural analysis show separate regimes of growth, namely I) wurtzite-like but having local lattice distortions in the vicinity of the Sc Ga substitutions for small x (x ≤ 0.17), II) a transitional regime for intermediate x, and III) cubic, rocksalt-like for large x (x ≥ 0.54). In regimes I and III, the direct optical transition decreases approximately linearly with increasing x but with an offset over region II. Importantly, it is found that for regime I, an anisotropic lattice expansion occurs with increasing x in which a increases much more than c. These observations support the prediction of Farrer and Bellaiche [Phys. Rev. B 66, 201203-1 (2002)] of a metastable layered hexagonal phase of ScN, denoted h-ScN.
Electronic structure and local distortions in epitaxial ScGaN films
JOURNAL OF PHYSICS-CONDENSED MATTER, 2014
High energy-resolution fluorescence-detected X-ray absorption spectroscopy and density functional theory calculations were used to investigate the local bonding and electronic structure of Sc in epitaxial wurtzite-structure Sc x Ga 1-x N films with x ≤ 0.059. Sc atoms are found to substitute for Ga atoms, accompanied by a local distortion involving an increase in the internal lattice parameter u around the Sc atoms. The local bonding and electronic structure at Sc are not affected strongly by the strain state or the defect microstructure of the films. These data are consistent with theoretical predictions regarding the electro nic structure of dilute Sc x Ga 1-x N alloys.
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.
Physical Review B, 2001
Experimental and ab initio computational methods are employed to conclusively show that ScN is a semiconductor rather than a semimetal; i.e., there is a gap between the N 2p and the Sc 3d bands. Previous experimental investigators reported, in agreement with band structure calculations showing a band overlap of 0.2 eV, that ScN is a semimetal while others concluded that it is a semiconductor with a band gap larger than 2 eV. We have grown high quality, single crystalline ScN layers on MgO͑001͒ and on TiN͑001͒ buffer layers on MgO͑001͒ by ultrahigh vacuum reactive magnetron sputter deposition. ScN optical properties were determined by transmission, reflection, and spectroscopic ellipsometry while in-situ x-ray and ultraviolet valence band photoelectron spectroscopy were used to determine the density of states ͑DOS͒ below the Fermi level. The measured DOS exhibits peaks at 3.8 and 5.2 eV stemming from the N 2p bands and at 15.3 eV due to the N 2s bands. The imaginary part of the measured dielectric function 2 consists of two primary features due to direct X-and ⌫-point transitions at photon energies of 2.7 and 3.8 eV, respectively. For comparison, the ScN band structure was calculated using an ab initio Kohn-Sham approach which treats the exchange interactions exactly within density-functional theory. Calculated DOS and the complex dielectric function are in good agreement with our ScN valence-band photoelectron spectra and measured optical properties, respectively. We conclude, combining experimental and computational results, that ScN is a semiconductor with an indirect ⌫ -X bandgap of 1.3Ϯ0.3 eV and a direct X-point gap of 2.4Ϯ0.3 eV.
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...
ScAlN nanowires: A cathodoluminescence study
Journal of Crystal Growth, 2009
Wurtzite ScAlN nanowires, grown on a scandium nitride (ScN) thin film by hydride vapor phase epitaxy (HVPE), were analyzed by energy dispersive analysis of X-rays (EDX), CL, high resolution transmission electron spectroscopy (HRTEM), and scanning electron microscopy (SEM). The wires were grown along the [0 0 0 1] axis, had an average length of 1 mm, a diameter between 50 and 150 nm, and a ScAlN composition with a 95:5 Al:Sc ratio. Cathodoluminescence studies on the individual wires showed a sharp emission near 2.4 eV, originating from the Sc atoms in the aluminum nitride (AlN) matrix. The formation of such a semiconducting ScAlN alloy could present a new alternative to InAlN for optoelectronic applications operating in the 200-550 nm range.
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.
Progress on new wide bandgap materials BGaN, BGaAlN and their potential applications
Quantum Sensing and Nanophotonic Devices IV, 2007
The development of wide band gap semiconductors extends their applications in optoelectronics devices to the UV domain. Compact lasers and high sensitivity APD detectors in UV range are currently needed for different applications such as, purification, covert communication and real time detection of airborne pathogens. Until now, the full exploitation of these potential materials has been limited by the lack of suitable GaN substrates. Recently, a novel class of materials has been reported based on BGaN and BAlN, potentially reducing the crystal defect densities by orders of magnitude compared to existing wide band gap heterostructures. Characteristics of these new alloys are similar to those of AlGaN materials with the advantage that these can be lattice matched to AlN and SiC substrates. In addition, these materials offer the possibility of using quaternary BAlGaN alloys at Ultra Violet (UV) wavelengths and hence lead to more degrees of freedom in designing sophisticated device structures. In this paper we describe the MOVPE growth conditions used to incorporate boron in GaN and AlGaN. Detailed characterization and analysis in terms of structural and electrical properties are discussed.