Raman Spectroscopy and Spectral Signatures of AlScN/Al2O3

Abstract

III-V solid solutions are sensitive to growth conditions due to their stochastic nature. The highly crystalline thin films require a profound understanding of the material properties and reliable means of their determination. In this work, we have investigated the Raman spectral fingerprint of Al1−xScxN thin films with Sc concentrations x = 0, 0.14, 0.17, 0.23, 0.32, and 0.41, grown on Al2O3(0001) substrates. The spectra show softening and broadening of the modes related to the dominant wurtzite phase with increasing Sc content, in agreement with the corresponding XRD results. We investigated the primary scattering mechanism responsible for the immense modes’ linewidths by comparing the average grain sizes to the phonon correlation length, indicating that alloying augments the point defect density. The low-frequency Raman bands were attributed to the confined spherical acoustic modes in the co-forming ScN nanoparticles. Temperature-dependent Raman measurements enabled the temperature coefficient of the E2(high) mode to be determined for all Sc concentrations for the precise temperature monitoring in AlScN-based devices.

Identification of compressive strain in thin ferroelectric Al1–x Sc x N films by Raman spectroscopy

“…Numbers of Raman measurements on c-axis oriented polycrystalline Al 1-x Sc x N films have been published. [16][17][18][19] A monotonic red shift in E 2 H and A1(LO) modes is reported while increasing the Sc atom concentration. 16) Therefore, the shift can be correlated to E c of the Al 1-x Sc x N films.…”

“…[16][17][18][19] A monotonic red shift in E 2 H and A1(LO) modes is reported while increasing the Sc atom concentration. 16) Therefore, the shift can be correlated to E c of the Al 1-x Sc x N films. The spectra broaden with higher Sc atom concentrations as large as 90 cm −1 in full-width half-maximum, which is a typical feature of alloyed material.…”

Reliable Accessibility of Intermediate Polarization States in Textured Ferroelectric Al0.66Sc0.34N Thin Film

“…[6,47,48] To estimate the W B and V* values of Al 0.66 Sc 0.34 N, we used the phonon frequency and our experimental P s value (1.81 × 10 13 Hz and 113 μC cm −2 ). [49] The barrier per unit volume and critical volume for nucleation were estimated to be 3.3×10 27 eV m −3 and 3.7×10 −28 m 3 , respectively. The remarkable reliability of the multi-level polarization states in the ferroelectric Al 0.66 Sc 0.34 N thin films is attributed to the high energy barrier per unit volume and small critical volume for nucleation.…”

“…[ 6,47,48 ] To estimate the W B and V* values of Al 0.66 Sc 0.34 N, we used the phonon frequency and our experimental P s value (1.81 × 10 13 Hz and 113 µC cm −2 ). [ 49 ] The energy barrier per unit volume and critical volume for nucleation were estimated to be 3.3×10 27 eV m −3 and 3.7×10 −28 m 3 , respectively.…”

Raman spectroscopy for thermal characterization of semiconductor devices

“…Raman spectroscopy enables temperature to be measured directly, and is grounded in solid-state fundamentals such as phonon distribution or anharmonic nature of the inter-atomic interaction. The latter was thoroughly investigated probing optical phonons and their temperature-dependent behavior in AlN in bulk and thin-film forms [8][9][10] enabling precise temperature determination from recorded Raman spectra. Moreover, the use of the microscope provides spatial resolution below 1 µm, which surpasses the resolution of standard thermal cameras, allowing precise spectral maps on the single-device level.…”