Near-Infrared to Vacuum Ultraviolet (VUV) Dielectric Properties of LaAlO 3

Transcription

1 Near-Infrared to Vacuum Ultraviolet (VUV) Dielectric Properties of LaAlO 3 Jacqueline Cooke 1, Tom Tiwald, Nuwanjula Samarasingha 1, Nalin Fernando 1, Stefan Zollner 1 1. Department of Physics, New Mexico State University, Las Cruces, NM J.A. Woollam Co., Lincoln, NE

2 Content Why measure LaAlO 3? What is LaAlO 3? Details about ellipsometry measurements LaAlO 3 transmission and absorption coefficients LaAlO 3 measured from near-infrared to ultraviolet Conclusion

3 We want to integrate and improve electronics and photonics LaAlO 3 is of interest as a substrate used for oxide epitaxial growth of thin films. It is mainly used as an insulator. Research is being conducted on the interface of LaAlO 3 when it is epitaxially grown on SrTiO 3. Because of this the properties of LaAlO 3 are useful yet not very well known. 3

4 What is LaAlO 3? Inorganic ceramic oxide. High-k dielectric. It has a perovskite cubic or rhombohedral crystal structure (ABO 3 ). Used as a single crystal substrate for growth of epitaxial thin films (normally for high temperature superconductors and magnetic or ferroelectric thin films). J.-X. Shen, A. Schleife, A. Janotti and C. G. Van de Walle, "Effects of La 5d and 4f states on the electronic and optical properties of LaAlO3," Physical Review B, vol. 94, no. 0503, pp. 1-7,

5 Ellipsometry: How does it work? We measure the change in the polarization state of light, when it is reflected by a flat surface. Monochromator or Interferometer (λ) detector J.A. Woollam polarizer Compensator analyzer NMSU Φ Sample 5

6 Spectroscopic Ellipsometry: Theory 6

7 Ellipsometric Data Psi Data Delta Data Brewster Angle at 65 Incidence Brewster Angle at 65 Incidence 7

8 Pseudo-Dielectric Function of LaAlO 3 Tauc-Lorentz Oscillator Model 1 E 0 n AE ( E n n 0 C( E E n0 ) n E C g ) E n for for ( E n ( E n E g E g ) ) E (ev) A Γ (ev) E g (ev) TL1 6.78(8) 18.9(7) ev 0.68(3) 4.73(8) UV pole 10.65(9) 30.8(8) ev IR pole 0.05(f) 0.019(4) ev Surface roughness: 13.76Å MSE: T. Willett-Gies, E. DeLong and S. Zollner, "Vibrational Properties of LaAlO3 from Fourier- Transform Infrared Ellipsometry," Thin Solid Films, vol. 571, no. Part 3, pp ,

9 Near-IR/UV Ellipsometry Data Pseudo-Absorption Coefficient and Transmission Data Surface roughness 4000 Å 9

10 Near-IR/UV Ellipsometry Data Cont. Direct Band Gap Indirect Band Gap Band Gap: 5.6 ev Indirect Gap: 5.55 ev Indirect Band Gap Direct Band Gap Consistent with Jimmy-Xyan Shen s and Seung-Gu Lim s publications J.-X. Shen, A. Schleife, A. Janotti and C. G. Van de Walle, "Effects of La 5d and 4f states on the electronic and optical properties of LaAlO3," Physical Review B, vol. 94, no. 0503, pp. 1-7, 016. S.-G. Lim, S. Kriventsov, T. N. Jackson, J. H. Haeni, S. D. G., B. A. M., R. Uecker, P. Reiche, J. L. Freeouf and G. Lucovsky, "Dielectric functions and optical bandgaps of high-k dielectric for metal-oxide-semiconductor field-effect transistors by far ultraviolet spectroscopic ellipsometry," Journal of Applied Physics, pp ,

11 VUV Experimental Data Psi Data Delta Data Brewster Angle at 65 Incidence Brewster Angle at 65 Incidence 11

12 VUV Pseudo-Dielectric Function Parametric Oscillator Model E (ev) A Γ (ev) Discont Left of CP Right of CP (f) Mid E (ev) Mid Amp (ev) Mid E (ev) Mid Amp (ev) (8) 9.847(8)eV 17.14(8) 0.833(3) 0.05(6) 0.008() 0.741(7) 0.053(3) 7.966(6) 1.754(8) ev 11.40(5) -0.49(9) 0.013(8) 0.05(4) 0.989() 0.98(6) 3 8.9(1) 4.6(6) ev (5) 0.645(4) 0.194(1) 0.194(1) 0.4().333(4) 4 1(f) UV pole 18(f) 350.3(3) ev IR pole 0.05(f) 0.07(4) ev Surface roughness:.91å MSE:

13 VUV Dielectric Function Crystal-field splitting of La(4f) states cause the seven bands to split into three directions. J.-X. Shen, A. Schleife, A. Janotti and C. G. Van de Walle, "Effects of La 5d and 4f states on the electronic and optical properties of LaAlO3," Physical Review B, vol. 94, no. 0503, pp. 1-7, 016. S.-G. Lim, S. Kriventsov, T. N. Jackson, J. H. Haeni, S. D. G., B. A. M., R. Uecker, P. Reiche, J. L. Freeouf and G. Lucovsky, "Dielectric functions and optical bandgaps of high-k dielectric for metal-oxide-semiconductor field-effect transistors by far ultraviolet spectroscopic ellipsometry," Journal of Applied Physics, pp ,

14 Conclusion We modeled the pseudo-dielectric function of LaAlO 3 using a Tauc-Lorentz oscillator. Calculated the band gap to be 5.6 ev and an indirect band gap to be 5.55 ev which is consistent with previously published works. We also modeled the pseudo-dielectric function using parametric oscillator model with three oscillators. From the model we determined the dielectric function of LaAlO 3. Absorption above 7 ev arises from O(p) valence band to the La(4f) conduction band states. 14

15 My Research Group ellipsometry.nmsu.edu 15