Cathodoluminescence and x-ray photoelectron spectroscopy of ScN: Dopant, defects, and band structure

Multifunctional Irradiation-Induced Defects for Enhancing Thermoelectric Properties of Scandium Nitride Thin Films

“…38,39 X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements have shown that both the unwanted n-type oxygen impurity and p-type Mg−hole doping do not introduce defect states inside the band gap, and the rigid band electronic structure remains unchanged with respect to the dopant introduction. 40,41 Despite the large power factor, the overall zT of ScN is relatively low at 0.17−0.30 in the 500−840 K temperature range due to its high thermal conductivity of ∼12−14 W/(m• K) at room temperature and 8.34 W/(m•K) at 800 K. 23,25,38 Efforts to reduce the thermal conductivity with solid-state alloying of ScN with other heavy metals such as niobium (Nb) and chromium (Cr) have been made. Thermal conductivity decreases to as low as 2.2 and 2.3 W/(m•K) at room temperature for Sc 1−x Nb x N and Sc 1−x Cr x N, respectively, due to the phonon scattering alloys.…”

“…The ScN thin films exhibit a high thermoelectric power factor of (2–3.5) × 10 –3 W/(m·K 2 ) in the 600–840 K temperature range that is higher than the power factor of most well-established thermoelectric materials such as Bi 2 Te 3 , Bi 2 Se 3 , and PbTe. − Such a high power factor in ScN arises from its high electron concentration in the (1–5) × 10 20 cm –3 range due to the presence of unwanted impurities such as oxygen and possible nitrogen vacancies. − Molecular beam epitaxy (MBE) and sputter-deposited ScN films also exhibit moderately large mobility in the 90–120 cm 2 /(V·s) range. , However, the highest mobility of 284 cm 2 /(V·s) is reported in hybrid vapor phase epitaxy (HVPE)-deposited ScN films . Mg–hole doping has been used recently to reduce the carrier concentration in ScN, and p-type ScN films with a large Seebeck coefficient are demonstrated. , X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and ultraviolet photoemission spectroscopy (UPS) measurements have shown that both the unwanted n-type oxygen impurity and p-type Mg–hole doping do not introduce defect states inside the band gap, and the rigid band electronic structure remains unchanged with respect to the dopant introduction. , …”

Synthesis and study of ScN thin films

“…Nonetheless, only recently, the primary contribution of oxygen incorporation has also been attributed to the surface oxidation [13,17]. Howbeit, nitrogen vacancies (V N ) are known to form a defect energy level at ≈1.26 eV above the valence band maxima at Γ point of the Brillouin zone [21]. In this context, it is to be mentioned here that significance of high T s depositions in supression of defects were found to be conflicting in literature [13,17,22,23], yet have not been highlighted so far.…”

“…Moreover, the extent of diffusion across the metalsemiconductor superlattice and/or multilayer interfaces will be comparatively high at a high T s regime [12], which could limit the device performances in practical applications. Additionally, interdiffusion across filmsubstrate interfaces are also pronounced at high T s depositions [21,25]. In view of this, contrary to high T s depositions, we adopted a room temperature deposited reactive magnetron sputtering technique for the synthesis of ScN thin film samples, as ScN favors thermodynamical growth conditions even at 298 K (∆H 0 f = -3.29 eV).…”

“…In order to probe the electronic structure of ScN, so far, usually x-ray photoelectron spectroscopy (XPS) or soft x-ray absorption spectroscopy (SXAS) at N Kedge (401.6 eV) and Sc L-edge (402.2 eV) were considered [21,[26][27][28]. But, since the two absorption edges appear very close to each other and moreover, both XPS and SXAS are known to be surface sensitive techniques [29], an alternative powerful technique such as xray absorption fine structure (XAFS) can provide better insight on the metrical parameters at atomic scale level.…”