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Proceedings Paper

Evaluation of intervalley energy of GaN conduction band by ultrafast pump-probe spectroscopy (Conference Presentation)
Author(s): Saulius Marcinkevicius; Tomas K. Uzdavinys; Humberto M. Foronda; Daniel E. Cohen; James S. Speck; Claude Weisbuch
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Paper Abstract

The energy difference between the lowest conduction band valleys is a fundamental semiconductor parameter affecting performance of electronic devices via intervalley electron scattering. Surprisingly, the intervalley energy (IVE) value in GaN is still disputed. Recent photoemission experiments showed that IVE is 0.90 – 0.95 eV, which is considerably smaller than the >2 eV values obtained by ab initio calculations. One of the suitable techniques to measure IVE is time-resolved spectroscopy. Excitation wavelength dependent photoluminescence and pump-probe transients allow pinpointing the onset of the intervalley scattering by increase of the electron relaxation time towards the bottom of the conduction band. In this work, we apply this approach by performing differential transmission (DT) and reflection (DR) measurements on n-GaN crystal. In DR, ultraviolet (UV) pump creates electrons in the Γ valley at energies around the scattering threshold, and the onset energy is determined by the change of the electron relaxation time towards the bottom of the conduction band. However, IVE evaluated using this technique is affected by the poor knowledge of the valence band dispersion at large k values. This problem is circumvented in the DT measurements, in which only conduction band states are involved. The DT decay time spectrum provided the IVE value of 0.97 ± 0.02 eV, close to the photoemission data. Comparison of DT and DR intervalley scattering onsets allowed estimating the hole mass as 1.4m0. Modelling of the DR transients with rate equations produced intra-and intervalley electron - LO phonon scattering times of 30 and 15 fs, respectively.

Paper Details

Date Published: 19 April 2017
PDF: 1 pages
Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 101040L (19 April 2017); doi: 10.1117/12.2250622
Show Author Affiliations
Saulius Marcinkevicius, KTH Royal Institute of Technology (Sweden)
Tomas K. Uzdavinys, KTH Royal Institute of Technology (Sweden)
Humberto M. Foronda, Univ. of California, Santa Barbara (United States)
Daniel E. Cohen, Univ. of California, Santa Barbara (United States)
James S. Speck, Univ. of California, Santa Barbara (United States)
Claude Weisbuch, Univ. of California, Santa Barbara (United States)


Published in SPIE Proceedings Vol. 10104:
Gallium Nitride Materials and Devices XII
Jen-Inn Chyi; Hiroshi Fujioka; Hadis Morkoç; Yasushi Nanishi; Ulrich T. Schwarz; Jong-In Shim, Editor(s)

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