Creation of supercooled exciton gas and transformation to electron-hole droplets in diamond

Abstract

We investigated the formation dynamics of electron-hole droplets in a high-purity single crystal diamond under photoexcitation near the band gap using time-resolved emission spectroscopy. Below the exciton Mott transition density, photogenerated carriers are cooled, and exciton emission appears within 30 ps. A broad emission band of droplets rises slowly, accompanied with a reduction in the exciton emission intensity in the next hundred picoseconds. This spectral change indicates the initial formation of low-temperature supersaturated exciton gas and subsequent spatial condensation of dense exciton gas into electron-hole droplets.

Low‐temperature excitons produced by two‐photon excitation in high‐purity diamond crystals

“…By fitting the spectral shape of edge emission with Maxwell-Boltzmann distributions assuming thermal equilibrium in the excitonic system, the temperatures of the excitons are found to be kept as low as the lattice temperature. This is in contrast to the cases with cathodoluminescence under electron-beam excitation or photoluminescence under one-photon excitation, where the lowest excitonic temperature reported is 36 K [4,5].…”

“…The accurate value of the direct gap is unknown, but it is believed to be around 7.3 eV [2]. Previously, we generated excitons via band-to-band excitation using laser pulses at a wavelength of 202 nm (6.1 eV) [7] or 218 nm (5.7 eV) [5]. In the present experiments, we employ excitation at 214 nm ( 1 5 8 ω = .…”

Formation and decay of electron-hole droplets in diamond

“…This intensity corresponds to an excitation of ϳ17 mJ/ cm 2 in the experiment. 8 It is seen from the figure that compared to the case of low excitation in Fig. 1, the exciton density decays during the first 20 ps.…”

“…It is also seen from the figures that the system reaches quasiequilibrium at about 120 ps and this quasi-equilibrium lasts about 200 ps. In the experiment the peak energy of the EHD emission band shifts toward the low energy side during first 200 ps, 8 which suggests that large clusters are formed at a longer time. Meanwhile from the fact that there is little change of the luminescence in the low energy regime, we conclude that the rate of the formation of small clusters from excitons and the rate of coalescence to large clusters are nearly the same.…”

Optical study of carrier diffusion and recombination in CVD diamond

“…The excitons are created from free electron-hole pairs during the first few picoseconds after photoexcitation [21]. Excitons can recombine via emission of TO phonon and UV photon.…”