Optical and transport measurement and first-principles determination of the ScN band gap

Abstract

The electronic structure of scandium nitride is determined by combining results from optical and electronic transport measurements with first-principles calculations. Hybrid functional (HSE06) calculations indicate a 0.92 eV indirect Γ-to-X band gap and direct transition energies of 2.02 and 3.75 eV at Γ-and X-points, respectively, while G o W o and GW o methods suggest 0.44-0.74 eV higher gap values. Epitaxial ScN(001) layers deposited on MgO(001) substrates by reactive sputtering exhibit degenerate n-type semiconductor properties with a temperature-independent electron density that is varied from N = 1.12-12.8×10 20 cm -3 using F impurity doping. The direct optical gap increases linearly with N from 2.18 to 2.70 eV, due to a Burstein-Moss effect. This strong dependence on N is likely the cause for the large range (2.03-3.2 eV) of previously reported gap values. However, here extrapolation to N = 0 yields 2.07±0.05 eV for the direct X-point transition of intrinsic ScN. A reflection peak at 3.80±0.02 eV is independent of N and in perfect agreement with the HSE06-predicted peak at 3.79 eV, associated with a high joint-density of states near the Γ-point. The electron mobility at 4 K is 100±30 cm 2 /Vs and decreases with temperature due to scattering at polar optical phonons with characteristic frequencies that decrease from 620 to 440±30 cm -1 with increasing N, due to free carrier screening. The transport and density-of-states electron effective mass, determined from measured intra and inter band transitions, respectively, are 0.40±0.02 m o and 0.33±0.02 m o , in good agreement with the firstprinciples predictions of m tr = 0.33±0.05 m o and m DOS = 0.43±0.05 m o . The ScN refractive index increases with increasing hν = 1.0-2.0 eV from 2.6-3.1 based on optical measurements and from 2.8-3.2 based on the calculated dielectric function. An overall comparison of experiment and simulation indicates (i) an overestimation of band gaps by GW methods but (ii) excellent agreement with a deviation of ≤0.05 eV for the hybrid functional and (iii) a value for the fundamental indirect gap of ScN of 0.92±0.05 eV.

Phonon thermal transport in transition-metal and rare-earth nitride semiconductors from first principles

“…[6] argued that they should be semiconducting based on the fact that the three s and d electrons from the metal atom combine with the five valence electrons from the nitrogen atom to give a closed shell. The semiconducting behavior for all three compounds has been confirmed through accurate screened exchange, hybrid functional DFT, and GW calculations [2,5,6,[8][9][10], with experimental confirmation for ScN [5,11].…”

The new nitrides: layered, ferroelectric, magnetic, metallic and superconducting nitrides to boost the GaN photonics and electronics eco-system

“…This is because its effective 111 lattice constant is (√2/2) ⋅ 4.505 ∼ 3.186 Angstrom, which has a ~0.1% lattice mismatch to 0001 GaN of lattice constant 3.189 Angstrom, compared to the ~17% lattice mismatch with 111 Silicon (of lattice constant 3.84 Angstrom). Furthermore, highly conductive degenerately doped n-type and p-type semiconducting ScN have also been realized [30][31] . Because of the cubic crystal structure of ScN, one would expect that the effect of incorporating Sc into AlN should be to a) distort the lattice structure from wurtzite towards Template for JJAP Regular Papers (Jan. 2014) 7 cubic, and b) shrink its bandgap.…”

Epitaxial NbC N1−(001) layers: Growth, mechanical properties, and electrical resistivity

“…99.999% pure N 2 was further purified with a MicroTorr purifier and introduced into the chamber with a needle valve to reach a constant pressure of 5 mTorr (=0.67 ± 0.02 Pa), measured with a capacitance manometer. Pure N 2 processing gas was chosen over the more conventional Ar + N 2 mixture because (i) the higher nitrogen partial pressure in pure N 2 provides a larger flux of nitrogen onto the growth surface and, (ii) pure N 2 is commonly used for the epitaxial growth of transition metal nitrides including TiN(001) [49,50], CrN(001) [51][52][53], ScN(001) [54], and Sc 1−x Al x N(001) [55]. Water-cooled 5-cm-diameter Nb and C targets with purities of 99.95% and 99.999%, respectively, were positioned both at 9.3 cm from the substrate at an angle of 45°with respect to the substrate surface normal.…”