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Room-temperature photoluminescence lifetime for the near-band-edge emission of (000 1 ˉ ) p-type GaN fabricated by sequential ion-implantation of Mg and H
摘要： Photoluminescence (PL) spectra of (000(cid:2)1) N-polar p-type GaN fabricated by using the sequential ion-implantation of Mg and H with subsequent high temperature annealing exhibited the near-band-edge (NBE) emission at 300 K. The longest PL lifetime (sPL) for the NBE emission of the sample with Mg and H concentrations of 1 (cid:2) 1019 and 2 (cid:2) 1020 cm(cid:3)3, respectively, annealed at 1230 (cid:4)C was 18 ps at 300 K. This value is almost comparable to that of the (0001) Ga-polar p-type Mg-doped GaN (p-GaN:Mg) homoepitaxial ?lm of the same Mg concentration. By correlating sPL and the concentration of major vacancy-type defects quanti?ed using positron annihilation spectroscopy, the electron capture-cross-section (rn) of the major nonradiative recombination centers (NRCs), namely, clusters of Ga vacancies (VGas) and N vacancies (VNs) such as (VGa)3(VN)3, is estimated at a few times 10(cid:3)13 cm2. This rn value is also comparable to that of the major NRCs in p-GaN:Mg epilayers, namely, VGa(VN)2 or VGa(VN)3, although the clustering sizes of the defects are different. These rn values are commonly larger than the hole capture-cross-section (rp ? 7 (cid:2) 10(cid:3)14 cm2) of the major NRCs, VGaVN divacancies, in n-type GaN.
关键词： p-type GaN,ion-implantation,Mg and H,electron capture-cross-section,photoluminescence,nonradiative recombination centers
更新于2025-09-23 15:21:21
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A statistical description of scattering at the quantum level
摘要： Quantum physics is undoubtedly the most successful theory of the microscopic world, yet the complexities which arise in applying it even to simple atomic and molecular systems render the description of basic collision probabilities a formidable task. For this reason, approximations are often employed, the validity of which may be restricted to given energy regimes and/or targets and/or projectiles. Now we have found that the lognormal function, widely used for the probability distribution of macroscopic stochastic events (as diverse as periods of incubation of and recovery from diseases, size of grains, abundance of species, fluctuations in economic quantities, etc.) may also be employed to describe the energy dependence of inelastic collisions at the quantum level (including ionization, electron capture and excitation by electrons, positrons, protons, antiprotons, etc.), by allowing for the relevant threshold energy. A physical interpretation is discussed in this article by analogy with the heat capacity of few-level systems in solid state physics. We find the generality of the analysis to extend also to nuclear reactions. As well as aiding the description of collision probabilities for quantum systems, this finding is expected to impact also on the fundamental understanding of the interface between the classical and quantum domains.
关键词： ionization,electron capture,nuclear reactions,lognormal distribution,excitation,inelastic collisions,quantum physics
更新于2025-09-23 15:21:21
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X-ray-assisted nuclear excitation by electron capture in optical laser-generated plasmas
摘要： X-ray-assisted nuclear excitation by electron capture (NEEC) into inner-shell atomic holes in a plasma environment generated by strong optical lasers is investigated theoretically. The considered scenario involves the interaction of a strong optical laser with a solid-state nuclear target leading to the generation of a plasma. In addition, intense x-ray radiation from the X-ray Free Electron Laser (XFEL) produces inner-shell holes in the plasma ions, into which NEEC may occur. As a case study, we consider the 4.85-keV transition starting from the 2.4-MeV long-lived 93mMo isomer that can be used to release the energy stored in this metastable nuclear state. We ?nd that the recombination into 2p1/2 inner-shell holes is most ef?cient in driving the nuclear transition. The generation of inner-shell holes while the plasma is at a temperature of a few hundred eV can allow optimal conditions for NEEC, which are otherwise reached for steady-state plasma conditions in thermodynamical equilibrium only at few keV. The combination of x-ray and optical lasers presents two advantages: First, NEEC rates can be maximized at plasma temperatures where the photoexcitation rate remains low. Second, with mJ-class optical lasers and an XFEL repetition rate of 10 kHz, the NEEC excitation number can reach ≈1 depleted isomer per second and is competitive with scenarios recently envisaged at petawatt-class lasers.
关键词： XFEL,optical laser-generated plasmas,X-ray-assisted nuclear excitation,NEEC,electron capture
更新于2025-09-12 10:27:22