Compositional dependence of linear and nonlinear optical response in crystalline hafnium zirconium oxide thin films

Abstract

Composition dependence of second harmonic generation, refractive index, extinction coefficient, and optical bandgap in 20 nm thick crystalline Hf1−xZrxO2 (0 ≤ x ≤ 1) thin films is reported. The refractive index exhibits a general increase with increasing ZrO2 content with all values within the range of 1.98–2.14 from 880 nm to 400 nm wavelengths. A composition dependence of the indirect optical bandgap is observed, decreasing from 5.81 eV for HfO2 to 5.17 eV for Hf0.4Zr0.6O2. The bandgap increases for compositions with x > 0.6, reaching 5.31 eV for Hf0.1Zr0.9O2. Second harmonic signals are measured for 880 nm incident light. The magnitude of the second harmonic signal scales with the magnitude of the remanant polarization in the composition series. Film compositions that display near zero remanent polarizations exhibit minimal second harmonic generation while those with maximum remanent polarization also display the largest second harmonic signal. The results are discussed in the context of ferroelectric phase assemblage in the hafnium zirconium oxide films and demonstrate a path toward a silicon-compatible integrated nonlinear optical material.

Determination of Hafnium Zirconium Oxide Interfacial Band Alignments Using Internal Photoemission Spectroscopy and X-ray Photoelectron Spectroscopy

“…6,[13][14][15]34 Recent spectroscopic ellipsometry measurements of an identically processed c-HZO film with a TaN bottom electrode show optical absorption features at 4.3 and 4.9 eV in addition to an indirect band gap of 5.2 eV. 41 The 4.9 eV defect band energy detected by spectroscopic ellipsometry is consistent with the onset of photoconduction in this work and suggests that it is the origin of the observed feature. (Additional details supporting this discussion may be found in the Supporting Information.…”

“…Possible origins of the increase in yield at around 4.9 eV in Figure include the onset of direct photoconduction in the HZO, subthreshold photoconduction due to the presence of band tail states in the HZO, or photoconduction due to photoemission from defects such as oxygen vacancies ,− close to the VB edge. The strong increase in yield at 4.9 eV occurs at a much lower energy than previous calculations and measurements of the band gaps of HfO 2 , ZrO 2 , and c-HZO (5.6–6, 5.4–5.8, and 5.4 eV, respectively), suggesting that photoconduction across the band gap of HZO is not the origin. ,− , Recent spectroscopic ellipsometry measurements of an identically processed c-HZO film with a TaN bottom electrode show optical absorption features at 4.3 and 4.9 eV in addition to an indirect band gap of 5.2 eV . The 4.9 eV defect band energy detected by spectroscopic ellipsometry is consistent with the onset of photoconduction in this work and suggests that it is the origin of the observed feature.…”

“…Summarized in Table are barrier heights (φ Bn ) measured in this work by IPE, XPS, and HAXPES along with metal work functions (Φ M ) from literature. Band diagrams based on IPE and XPS results are shown in Figure , assuming a HZO band gap of 5.2 eV . With the exception of the Ta interface, the estimated XPS barriers are significantly lower than the IPE barriers (0.8–2 eV) with an average offset of approximately 1.1 eV.…”

“…Band diagrams based on IPE and XPS results are shown in Figure 8, assuming a HZO band gap of 5.2 eV. 41 With the exception of the Ta interface, the estimated XPS barriers are significantly lower than the IPE barriers (0.8−2 eV) with an average offset of approximately 1.1 eV. The HAXPES ϕ bn barrier values for Pt and Au are also much lower than the IPE values.…”

Optical Second-Harmonic Polarimetry on Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 Interfaces

“…Therefore, the estimated average laser intensity is about 5.7 × 10 5 W/m 2 , and the peak intensity is about 17 × 10 15 W/m 2 . These numbers, provided that the absorption length at 800 nm is much larger than the film thickness, 29 ensure that the optical excitation is weak enough to assume a negligible effect on the fundamental properties of the material. The iSHG signal is generated when the beam is reflected by the sample surface.…”