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-doped two-dimensional semiconductor quantum wells
摘要： We present a theoretical study of photoabsorption in n-doped two-dimensional (2D) and quasi-2D semiconductors that takes into account the interaction of the photocreated exciton with Fermi-sea (FS) electrons through (i) Pauli blocking, (ii) Coulomb screening, and (iii) excitation of FS electron-hole pairs—that we here restrict to one. The system we tackle is thus made of one exciton plus zero or one FS electron-hole pair. At low doping, the system ground state is predominantly made of a 'trion-hole'—a trion (two opposite-spin electrons plus a valence hole) weakly bound to a FS hole—with a small exciton component. As the trion is poorly coupled to photon, the intensity of the lowest absorption peak is weak; it increases with doping, thanks to the growing exciton component, due to a larger coupling between two-particle and four-particle states. Under a further doping increase, the trion-hole complex is less bound because of Pauli blocking by FS electrons, and its energy increases. The lower peak then becomes predominantly due to an exciton dressed by FS electron-hole pairs, that is, an exciton-polaron. As a result, the absorption spectra of n-doped semiconductor quantum wells show two prominent peaks, the nature of the lowest peak turning from trion-hole to exciton-polaron under a doping increase. Our work also nails down the physical mechanism behind the increase with doping of the energy separation between the trion-hole peak and the exciton-polaron peak, even before the anticrossing, as experimentally observed.
关键词： Fermi sea,trion-hole complex,exciton-polaron,photoabsorption,Pauli blocking,n-doped semiconductors,Coulomb screening
更新于2025-09-23 15:23:52
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Fundamental understanding of chemical processes in extreme ultraviolet resist materials
摘要： New photoresists are needed to advance extreme ultraviolet (EUV) lithography. The tailored design of efficient photoresists is enabled by a fundamental understanding of EUV induced chemistry. Processes that occur in the resist film after absorption of an EUV photon are discussed, and a new approach to study these processes on a fundamental level is described. The processes of photoabsorption, electron emission, and molecular fragmentation were studied experimentally in the gas-phase on analogs of the monomer units employed in chemically amplified EUV resists. To demonstrate the dependence of the EUV absorption cross section on selective light harvesting substituents, halogenated methylphenols were characterized employing the following techniques. Photoelectron spectroscopy was utilized to investigate kinetic energies and yield of electrons emitted by a molecule. The emission of Auger electrons was detected following photoionization in the case of iodo-methylphenol. Mass-spectrometry was used to deduce the molecular fragmentation pathways following electron emission and atomic relaxation. To gain insight on the interaction of emitted electrons with neutral molecules in a condensed film, the fragmentation pattern of neutral gas-phase molecules, interacting with an electron beam, was studied and observed to be similar to EUV photon fragmentation. Below the ionization threshold, electrons were confirmed to dissociate iodo-methylphenol by resonant electron attachment.
关键词： photoabsorption,molecular fragmentation,electron emission,photoresists,mass-spectrometry,Auger electrons,photoelectron spectroscopy,EUV lithography,resonant electron attachment,halogenated methylphenols
更新于2025-09-23 15:21:01
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Indirect predissociation of highly excited singlet states of N <sub/><b>2</b> </sub>
摘要： Indirect predissociation of the b(cid:2) 1(cid:1)+u (v = 20) level of N2 is studied experimentally by vacuum-ultraviolet photoabsorption employing synchrotron radiation and a Fourier-transform spectrometer, and interpreted with the aid of a quantitative model of interacting 1(cid:2)u and 1(cid:1)+u, bound and unbound states which solves the coupled Schr?dinger equation. An observed rotationally-localised peak in the b(cid:2)(20) predissociation linewidths is identi?ed by the model as arising from an interaction with a strongly predissociated and unobserved bound level of the mixed c3 1(cid:2)u and o3 1(cid:2)u Rydberg states. This leads to the dissociation of b(cid:2)(20) into the continuum of the b 1(cid:2)u valence state. The residual observed predissociation of b(cid:2) 1(cid:1)+u (v = 20) apart from the rotationally-localised peak cannot be explained by a mechanism of 1(cid:2)u and 1(cid:1)+u interaction, and must involve states of higher multiplicity.
关键词： Fourier-transform spectrometer,coupled Schr?dinger equation,vacuum-ultraviolet photoabsorption,N2,Indirect predissociation,synchrotron radiation
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Improved Photoabsorption in Thin Gallium Arsenide Solar Cells using Light Trapping Techniques
摘要： Thin absorbers for space photovoltaics can achieve higher radiation tolerance, however, they suffer from reduced photoabsorption as the active region is thinned. In this work, increasing the photoabsorption in thin single junction n-i-p GaAs solar cells have been investigated by applying different light trapping structures at the rear of the cell. The main focus has been to develop a random surface texture that varies in three dimensions to increase light scattering and the effective optical path length. From the EQE, the random back surface reflector was successfully applied to a 1.1 μm thick GaAs solar cell which resulted in a notable 38% increase in current output, when compared to the GaAs baseline cell on its substrate without a BSR. The random texture has shown the capability to maintain the current output in the 1.1 μm thick GaAs absorber and shows promise for enhancing the photoabsorption in thin GaAs absorbers that approach the sub-μm thickness regime.
关键词： photoabsorption,thin GaAs solar cells,light trapping,random maskless texture,radiation tolerance
更新于2025-09-16 10:30:52
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Solvent-assisted excited state proton transfer and photoacidity of 2-hydroxypyridine. A nonadiabatic dynamics study
摘要： Reactions involving proton transfer, especially those taking place in excited states (ESPT), received considerable attention. These reactions underlie many biological and biochemical processes that are vital to life. DNA mutations excited state funnelling and transport phenomena are just examples. Among many molecules undergoing this type of photoreactions, phenols show a unique property, the so-called photoacidity. In the present communication, solvent (methanol and ammonia) assisted excited state proton transfer and photo acidity of 2-hydroxypyridine (2HP) are investigated at the DFT M06-2X / def2pvv level of theory. Excited states of 2HP and its complexes with methanol and ammonia were examined at two levels. First, sampling a Wigner distribution of 300 points, the photoabsorption spectra were simulated within the nuclear ensemble approximation. Second, simulation of the dynamics of the excited states with the surface hopping method. Several separate spectral windows with three hundred trajectories each, were considered. Lifetime of excited states and photochemical channels observed were discussed.
关键词： nonadiabatic dynamics,photoacidity,Excited state proton transfer (ESPT),photoabsorption spectrum,2-hydroxypyridine
更新于2025-09-09 09:28:46