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Radiative lifetime of boron-bound excitons in diamond studied by ultraviolet absorption

le 19 mars 2019

Mardi 19 mars 2019
à 11h
GEMaC, salle 4109
Bat. Fermat,
45 avenue des Etats-Unis
78035 Versailles cedex

par Y. Kubo de l'Université de Tokyo

Recent progresses in doping control techniques for diamond accelerate the use of doped diamond in electronic applications. Because boron impurities play a unique and important role as acceptors providing p-type conductivity, boron-doped diamond has been intensely studied, e.g. by Hall effect measurements and infrared spectroscopy [1]. On the other hand, the boron-bound exciton―a complex formed due to capture of an exciton at a boron impurity―has so far been discussed only on the basis of cathodoluminescence (CL) [2, 3]. Although the bound excitons dominate the luminescence spectra, no absorption spectra had been measured so far. This situation impedes uncovering the bound-exciton recombination processes, which should be crucial for a deep understanding of its physical properties and optimization of diamond- based devices.

In this study, we measured the absorption spectrum due to boron-bound excitons in diamond near the absorption edge of the intrinsic diamond [Fig. 1(a)]. The investigated sample of 250 µm thickness was synthesized by the plasma-assisted chemical vapor deposition (CVD) method with the boron concentration of 1.8×1018 cm-3 [4]. Based on the absorption cross section as shown in Fig. 1(b), the oscillator strength of the no-phonon (NP) lines was determined to be 3.0×10-5. This value satisfies the scaling law established for silicon between the oscillator strength and the localization energy. More
importantly, we also assessed the oscillator strength of 1.2×10-3 for the transverse optical (TO) phononassisted transition, which dominates the spectra and provides an associated radiative lifetime of 1.8 µs. The obtained radiative lifetime is two orders of magnitude shorter than that in silicon.

Our first successful measurements of ultraviolet absorption facilitate the prediction of radiative and non-radiative lifetimes of bound excitons in variously doped diamond by using scaling laws [5].

Figure 1 – (a) Absorption spectra of boron-doped (solid line) and intrinsic (dotted line) diamond near the band edge. (b) Enlarged NP lines showing the absorption cross section by the shaded area.

1. K. Thonke, Semicond. Sci. Technol. 18 (2013), S20.
2. J. Barjon, et al. Phys. Rev. B 93 (2016), 115202.
3. J. Barjon, Phys. Status Solidi A 214 (2017), 700402.
4. R. Issaoui, et al. Appl. Phys. Lett. 100 (2012), 122109.
5. Y. Kubo, et al. submitted to Appl. Phys. Lett..