Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBimolecular theory of non-radiative recombination in semiconductors with disorder
71
0
0.0
(
0
)
Authors
Oleg Rubel
Ask ChatGPT about the research
No Arabic abstract
The original Shockley-Read-Hall recombination statistics is extended to include recombination of localized excitations. The recombination is treated as a bimolecular process rather than a monomolecular recombination of excitons. The emphasis is placed on an interplay between two distinct channels of radiative recombination (shallow localized states vs extended states) mediated by trapping of photogenerated charge carriers by non-radiative centers. Results of a numerical solution for a given set of parameters are complemented by an approximate analytical expression for the thermal quenching of the photoluminescence intensity in non-degenerate semiconductors derived in the limit of low pump intensities. The merit of a popular double-exponential empirical function for fitting the thermal quenching of the photoluminescence intensity is critically examined.
rate research
Read More
Individual dislocations in an ultra-pure GaAs epilayer are investigated with spatially and spectrally resolved photoluminescence imaging at 5~K. We find that some dislocations act as strong non-radiative recombination centers, while others are efficient radiative recombination centers. We characterize luminescence bands in GaAs due to dislocations, stacking faults, and pairs of stacking faults. These results indicate that low-temperature, spatially-resolved photoluminescence imaging can be a powerful tool for identifying luminescence bands of extended defects. This mapping could then be used to identify extended defects in other GaAs samples solely based on low-temperature photoluminescence spectra.
Magnetic properties of Ga$_{1-x}$Mn$_x$N are studied theoretically by employing a tight binding approach to determine exchange integrals $J_{ij}$ characterizing the coupling between Mn spin pairs located at distances $R_{ij}$ up to the 16th cation coordination sphere in zinc-blende GaN. It is shown that for a set of experimentally determined input parameters there are no itinerant carriers and the coupling between localized Mn$^{3+}$ spins in GaN proceeds via superexchange that is ferromagnetic for all explored $R_{ij}$ values. Extensive Monte Carlo simulations serve to evaluate the magnitudes of Curie temperature $T_mathrm{C}$ by the cumulant crossing method. The theoretical values of $T_mathrm{C}(x)$ are in quantitative agreement with the experimental data that are available for Ga$_{1-x}$Mn$_x$N with randomly distributed Mn$^{3+}$ ions with the concentrations $0.01 leq x leq 0.1$.
A microscopic approach is developed to compute the excitonic properties and the corresponding terahertz response for semiconductors characterized by anisotropic effective masses. The approach is illustrated for the example of germanium where it is shown that the anisotropic electron mass in the L-valley leads to two distinct terahertz absorption resonances separated by 0.8 meV.
Organic semiconductors have generated considerable interest for their potential for creating inexpensive and flexible devices easily processed on a large scale [1-11]. However technological applications are currently limited by the low mobility of the charge carriers associated with the disorder in these materials [5-8]. Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility. Here we take a radically different path to solving this problem, namely by injecting carriers into states that are hybridized to the vacuum electromagnetic field. These are coherent states that can extend over as many as 10^5 molecules and should thereby favour conductivity in such materials. To test this idea, organic semiconductors were strongly coupled to the vacuum electromagnetic field on plasmonic structures to form polaritonic states with large Rabi splittings ca. 0.7 eV. Conductivity experiments show that indeed the current does increase by an order of magnitude at resonance in the coupled state, reflecting mostly a change in field-effect mobility as revealed when the structure is gated in a transistor configuration. A theoretical quantum model is presented that confirms the delocalization of the wave-functions of the hybridized states and the consequences on the conductivity. While this is a proof-of-principle study, in practice conductivity mediated by light-matter hybridized states is easy to implement and we therefore expect that it will be used to improve organic devices. More broadly our findings illustrate the potential of engineering the vacuum electromagnetic environment to modify and to improve properties of materials.
This article reviews the current status of spin dynamics in semiconductors which has achieved a lot of progress in the past years due to the fast growing field of semiconductor spintronics. The primary focus is the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in time domain and spin diffusion and transport in spacial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is reviewed comprehensively.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
