Intrinsic Carrier Parameters and Optical Carrier Injection Method in High-Purity Diamonds

Diamond attracts increasing attentions as a semiconductor, since high-purity synthesized diamonds have become commercially available in these decades. For appropriate design of any devices, the basic carrier transport parameters should be known. However, it has been difficult to determine carrier parameters in diamond, because the controlled doping and Ohmic contact formation have been hard to achieve. In this chapter, a modern experimental method to measure basic carrier parameters, such as the effective mass, scattering times, and mobility of intrinsic diamonds, is introduced. The method, i.e., nanosecond time-resolved cyclotron resonance (TRCR), is applicable to optically injected carriers in intrinsic diamonds without wire connection. Following the key technique of optical carrier injection, detailed analysis methods for the cyclotron resonance spectra are introduced. The extracted basic parameters of diamond are summarized in comparison to those of silicon and germanium in the same group-IV semiconductor family. This is worthy for triggering further ideas in application-oriented researches using widespread materials

Condensation of Excitons in Cu2O at Ultracold Temperatures: Experiment and Theory

We present experiments on the luminescence of excitons confined in a potential trap at milli-Kelvin bath temperatures under cw-excitation. They reveal several distinct features like a kink in the dependence of the total integrated luminescence intensity on excitation laser power and a bimodal distribution of the spatially resolved luminescence. Furthermore, we discuss the present state of the theoretical description of Bose-Einstein condensation of excitons with respect to signatures of a condensate in the luminescence. The comparison of the experimental data with theoretical results with respect to the spatially resolved as well as the integrated luminescence intensity shows the necessity of taking into account a Bose-Einstein condensed excitonic phase in order to understand the behaviour of the trapped excitons.Comment: 41 pages, 23 figure

Resonant creation of indirect excitons in diamond at the phonon-assisted absorption edge

We have developed a new scheme for generating cold and high-density excitons in diamond by resonant excitation at the phonon-assisted absorption edge. Both the thermalization of excitons between fine-structure states and the effective temperature are examined with the tuning of the photon energy. The down-conversion rate for the excitons in the fine-structure states is found to be 3.5 ns independent of the photon energy, which means that the lowest-energy dark exciton can be created within a time scale comparable to its lifetime via the generation of a higher-energy bright exciton. With careful choice of excitation photon energy, we have achieved an electron-hole pair density of $2\times10^{19}\ \text{cm}^{-3}$ while maintaining the effective excitonic temperature below 15 K

Radiative lifetime of boron-bound excitons in diamond

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Quantitative relevance of substitutional impurities to carrier dynamics in diamond

International audienceWe have quantified substitutional impurity concentrations in synthetic diamond crystals down to sub-partsper-billion levels. The capture lifetimes of electrons and excitons injected via photoexcitation were compared for several samples with different impurity concentrations. Based on the assessed impurity concentrations, we have determined the capture cross section of electrons for boron impurity, σ A = 1 × 10 −14 cm 2 , and that of excitons for nitrogen impurity, σ ex D = 3 × 10 −14 cm 2. The general tendency of the mobility values for different carrier species is successfully reproduced by including carrier scattering by impurities and excitons

Phonon-assisted transitions of bound excitons in diamond: Analysis by mirror symmetry

International audienceThis study aims at a quantitative understanding of the optical spectra taken from bound excitons weakly coupled to phonons in indirect semiconductors, which had been missing for decades. Insights on the properties of excitons bound at neutral acceptor impurities are obtained by analyzing the spectra reported for diamond with appropriate boron doping [Y. Kubo, Appl. Phys. Lett. 114, 132104 (2019)APPLAB0003-695110.1063/1.5089894]. We focus on the mirror symmetry holding between phonon-assisted absorption and luminescence simultaneously regarding energies, linewidths, and intensities. New analytic expressions are proposed to reproduce the spectra of phonon-assisted recombination lines. The detailed analysis reveals the contribution from excited bound-exciton states whose origin is discussed and modeled. Taking them into account improves simulation of the bound-exciton optical spectra in indirect band-gap semiconductors up to a quantitative level

Low-temperature mobility-lifetime product in synthetic diamond

The mobility-lifetime (μτ) product is an important parameter that determines the performance of electronic and photonic devices. To overcome the previously reported difficulties in measuring the μτ product at cryogenic temperatures, we implement a time-resolved cyclotron resonance method to determine the carrier lifetime τ. After clarifying the difference between the AC and DC mobilities measured by cyclotron resonance and time-of-flight methods, respectively, we demonstrate an inverse temperature dependence of the μτ product. The highest recorded μτ product of 0.2 cm2/V, which is approximately 100 times the room-temperature value, was obtained at 2 K for chemical-vapor-deposition diamond of the highest currently available purity