Radiative Auger Process Research Articles

Optically driving the radiative Auger transition

In a radiative Auger process, optical decay leaves other carriers in excited states, resulting in weak red-shifted satellite peaks in the emission spectrum. The appearance of radiative Auger in the emission directly leads to the question if the process can be inverted: simultaneous photon absorption and electronic demotion. However, excitation of the radiative Auger transition has not been shown, neither on atoms nor on solid-state quantum emitters. Here, we demonstrate the optical driving of the radiative Auger transition, linking few-body Coulomb interactions and quantum optics. We perform our experiments on a trion in a semiconductor quantum dot, where the radiative Auger and the fundamental transition form a Λ-system. On driving both transitions simultaneously, we observe a reduction of the fluorescence signal by up to 70%. Our results suggest the possibility of turning resonance fluorescence on and off using radiative Auger as well as THz spectroscopy with optics close to the visible regime.

The characteristic radiation of copper Kβ including radiative Auger processes

Two characterisations of the Cu Kβ1,3 spectrum are developed, which are robust and transferable to other experimental x-ray geometries. By observing and considering the significant contribution of radiative Auger emission to the Kβ profile, we obtain an improved and more robust characterisation. The contribution of the KM2,3M4,5 and KM2,3N1 radiative Auger satellites to the Kβ1,3 spectrum is measured to be 1.96%. The contribution of radiative Auger emission is often significant and should be included in defining characteristic x-ray spectra. This is a step in the renewed efforts to resolve inconsistencies in characteristic x-ray spectra between theory and common experimental geometries. The spectrum was measured using a rotating anode, monolithic Si channel-cut double-crystal monochromator and backgammon detector. The experimental setup provides insight into the portability of spectral characterisations of x-ray spectra.

Radiative Auger process in the single-photon limit.

In a multi-electron atom, an excited electron can decay by emitting a photon. Typically, the leftover electrons are in their ground state. In a radiative Auger process, the leftover electrons are in an excited state and a redshifted photon is created1-4. In a semiconductor quantum dot, radiative Auger is predicted for charged excitons5. Here we report the observation of radiative Auger on trions in single quantum dots. For a trion, a photon is created on electron-hole recombination, leaving behind a single electron. The radiative Auger process promotes this additional (Auger) electron to a higher shell of the quantum dot. We show that the radiative Auger effect is a powerful probe of this single electron: the energy separations between the resonance fluorescence and the radiative Auger emission directly measure the single-particle splittings of the electronic states in the quantum dot with high precision. In semiconductors, these single-particle splittings are otherwise hard to access by optical means as particles are excited typically in pairs, as excitons. After the radiative Auger emission, the Auger carrier relaxes back to the lowest shell. Going beyond the original theoretical proposals, we show how applying quantum optics techniques to the radiative Auger photons gives access to the single-electron dynamics, notably relaxation and tunnelling. This is also hard to access by optical means: even for quasi-resonant p-shell excitation, electron relaxation takes place in the presence of a hole, complicating the relaxation dynamics. The radiative Auger effect can be exploited in other semiconductor nanostructures and quantum emitters in the solid state to determine the energy levels and the dynamics of a single carrier.

Auger processes in a single quantum dot.

Radiative Auger processes in the single-photon limit provide insights in single particle states of quantum dots, which remain otherwise inaccessible.

Two-electron-satellite transition of donor bound exciton in ZnO: Radiative Auger effect

Two-electron-satellite (TES) transition of donor bound exciton (D0X) is an interesting many-body quantum process. In this letter, precise luminescence spectra and temperature behaviors of the TES transition of aluminum bound exciton in two kinds of zinc oxide single crystals were investigated in detail. It is found that the TES transition can be treated as a radiative Auger process in which the temperature dependence of the emission intensity of the transition can be fitted very well with a model taking into account the temperature dependent Auger term and thermal dissociation of the D0X excitons.

Transient photoluminescence of shallow donor bound excitons in GaN

We present a detailed study of photoluminescence transients for neutral donor bound excitons (DBEs) in GaN, notably the ${\text{O}}_{\text{N}}$ donor DBE at 3.4714 eV and the ${\text{Si}}_{\text{Ga}}$ DBE at 3.4723 eV. The studied samples are thick strain free nominally undoped bulk GaN samples, with a spectroscopic linewidth $<0.5\text{ }\text{meV}$ at 2 K. The photoluminescence (PL) decay curves for these no-phonon (NP) lines are strongly nonexponential, and do not allow a proper assessment of the characteristic BE decay time. The decay of the LO-phonon replicas as well as the so-called two-electron transitions (TETs) at lower energies show a nicely exponential behavior, and allow extraction of DBE decay times of about 1.1 ns for the Si DBE and 1.8 ns for the O DBE, respectively. The initial nonexponential decay behavior of the NP lines has been studied in both the common front surface excitation-detection mode and with detection in transmission through the sample. This initial decay is explained as related to scattering processes in the near surface region, involving the DBEs and free excitons (FEs). Light scattering processes may also contribute to this complex decay shape. The DBE-LO-phonon decay does not discriminate between the O and Si DBEs because of spectral overlap involving different LO modes. The TET decays at 2 K are very different for transitions related to the DBE ground state and DBE excited states (going to $p$-like donor final states), for $T>10\text{ }\text{K}$ thermalization between the DBE ground state and DBE excited states produces a common decay time. Thermalization between free and bound excitons appears to occur above about 20 K, when the DBE decay follows the FE decay. A simple two-level modeling of exciton capture and recombination for the PL decay curves of the FE and the DBEs, as commonly used in the literature, is shown to be generally inadequate. A broad PL background in the TET spectral region is suggested to be related to a radiative Auger process, where the DBEs recombine while leaving the donors ionized.

Radiative Auger Effect and Extended X-Ray Emission Fine Structure (EXEFS)

Radiative Auger spectra are weak X-ray emission spectra near the characteristic X-ray lines. Radiative Auger process is an intrinsic energy-loss process in an atom when a characteristic X-ray photon is emitted, due to an atomic many-body effect. The energy loss spectra correspond to the unoccupied conduction band structure of materials. Therefore the radiative Auger effect is an alternative tool to the X-ray absorption spectroscopy such as EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure), and thus it is named EXEFS (Extended X-ray Emission Fine Structure). By the use of a commercially available X-ray fluorescence spectrometer or an electron probe microanalyzer (EPMA), which are frequently used in materials industries, we can obtain an EXEFS spectrum within 20 min. The radiative Auger effect, as an example, demonstrates that the study on atomic many-body effects has become a powerful tool for crystal and electronic structure characterizations. The EXEFS method has already been used in many industries in Japan. Reviews about the applications and basic study results on the radiative Auger effect are reported in this paper.

K-MM radiative-Auger transition probability calculationsfor Ca, Ti and Cr

The K-MM radiative-Auger transition probabilities for Ca, Tiand Cr were calculated using time-dependent perturbation theory.The atom plus the free radiation field are considered as beingone system and the transition of one state of the atom toanother results from the interaction between components of thissystem. The perturbing Hamiltonian is taken as the sum of theinteraction between the electrons participating directly in theprocess and their interaction with the radiation field. Underthis approach, the radiative-Auger process is describedconsidering second-order terms in time-dependent perturbationtheory series. The calculations were performed using screenedhydrogenic wavefunctions to describe the state of the atom.The results obtained are compared with recent experimental dataand other theoretical calculations.

Peculiarities of excitation of Ce-emission in core region of chlorine perovskites

Excitation spectra of Ce-doped KCaCl3, RbCaCl3, CsSrCl3 and CsCaCl3 crystals were studied at 300 and 9K in the 4–35eV spectral range using synchrotron radiation. Peculiarities of the excitation spectra in the region of the uppermost core are considered from the view point of feasibility of the energy transfer from the core excitons and holes to Ce-centers. The possible channels for excitation of the activator luminescence are assumed for the CsCaCl3 and CsSrCl3 crystals exhibiting core-valence luminescence (CVL) as follows: (i) the reabsorption of the CVL by Ce-centers; (ii) the creation of the valence holes on account of radiative decay of core excitations via CVL and (iii) the migration of the core holes. All these schemes are distinctly impossible for the CVL-free KCaCl3 and RbCaCl3 crystals where core excitations decay just through the non radiative Auger-process.

Analysis of the light-current relationships in the optimized planar buried mesa ridge (PBMR) InGaAsP laser

Inclusion of the optimized composite waveguide concept in the InGaAsP/InP PBMR laser construction resulted in an improvement of the differential quantum efficiency value by more than ten per cent. Analysis of the kinetic equations for the carrier and photon populations was used to evaluate various contributions (radiative recombination, Auger processes, electron drift and parasitic leakage currents) to the threshold current in the optimized PBMR geometry.

Virtual Raman KLL radiative Auger process.

By x-ray bombardment of metal single crystals, x rays of KLL radiative Auger electrons are observed on the low-energy side of the K\ensuremath{\alpha} lines. Unlike the usual radiative Auger process where x-ray continua result, we find x rays in the form of sharp lines that originate from a hitherto unobserved virtual Raman process. To our surprise this is the dominant radiative Auger process in the investigated single crystals.

The Kα1,2X-ray spectra of the 3d transition metals Cr, Fe, Co, Ni and Cu

The electron-excited K alpha 1 and K alpha 2 X-ray spectra of the metals Cr, Fe, Co, Ni and Cu have been investigated with the aid of curved-crystal spectrometry, and are compared with respect to asymmetry indices and FWHM values. Three alternative approximations have been applied in the calculations, i.e. one symmetric lorentzian per line, two symmetric lorentzians per line and two skew lorentzians per line. Fractional contributions to the extra non-line intensity from the multiplet structure, the skewness effect and from radiative Auger processes have been evaluated, indicating that the multiplet structure is of major importance for Cr and Fe, while radiative Auger processes are dominant for Ni and Cu. The three effects yield about the same magnitude of extra non-line intensity in the case of Co. The radiative Auger processes give a relative intensity of approximately the same magnitude, i.e. approximately 8% of the main line peak intensity, for all the elements in question and for both the alpha 1 line and the alpha 2 line.

Origin of low-energy satellites in K X-ray spectra. I. α-region

In view of the success of the theory of radiative Auger processes, the authors have undertaken a review of all the available data on low-energy satellites of X-ray spectra to find suitable transitions to assign to them and thereby bring some systematisation to the rather scattered data. The results of the study on Kalpha satellites are given. Many low-energy satellites of K-spectra have been assigned to K-L3M4,5 and K to L2M4,5 radiative Auger transitions.

Radiative auger transitions of iron compounds

Weak X-ray emission lines from a series of iron compounds with energies in the range 5900–6970 eV can be rationalised as due to the K → M 2 radiative Auger process. A peak was also observed at ca. 6930 eV, of unknown origin which had a very low intensity in some low-spin compounds.

Excited States of Bound Excitons and Neutral Donors in CdS

A technique employing a monochromator to select the incident photon energy and a spectrometer to analyze the low temperature photoluminescence of CdS crystals has proven to be valuable, both in analyzing the usual photoluminescent spectra and in obtaining new information on excited states of bound excitons and excited states of neutral donors in the crystal. An accurate measurement of the donor energy levels and the donor binding energy gave a binding energy for the Cl donor in CdS of 33.0 ± 0.2 meV. Energies of excited states of the bound exciton complexes were also measured and for the bound exciton – neutral donor complex (I2 complex) some seven excited state levels were found. One type of radiative decay observed for this I2 complex is a radiative Auger process. This has important consequences in interpreting photoconductivity spectra.