arXiv subjects

Agata Kaminska

Publications and source records attributed to Agata Kaminska.

8 recordsLinked to original sources

arXiv2026

Role of quasi-Fermi levels in Si- and Mg-related optical absorption in nitride laser diodes (LDs): material context

Optical absorption and reabsorption of light emitted from active regions in nitride laser diodes (LDs) have been shown to reduce the light extraction efficiency of these devices. It was proven that the presence of Si and Mg may considerably increase the optical absorption. This effect is much stronger in the high-energy (short-wavelength) range of the spectrum. The absorption increase is directly related to the ionization of the Si donor and Mg acceptor levels, which are controlled by the electron and hole quasi-Fermi levels. It is shown that the absorption may be increased because of the higher ionization of Mg caused by the compensation in the p-type region and the high ionization of Si in the n-type region. It was explained theoretically why optical efficiency is increased by removal of doping in waveguides. It was also shown that good material quality leads to a low absorption level, especially in the Mg-doped p-type part of the device.

cond-mat.mtrl-sci↗

arXiv2025

Strain distribution in GaN/AlN superlattices grown on AlN/sapphire templates: comparison of X-ray diffraction and photoluminescence studies

Series of GaN/AlN superlattices (SLs) with various periods and the same thicknesses of GaN quantum wells and AlN barriers have been investigated. X-ray diffraction, photoluminescence (PL) and transmission electron microscopy (TEM) techniques were used to study the influence of thickness of AlN and GaN sublayers on strain distribution in GaN/AlN SL structures. Detailed X-ray diffraction measurements demonstrate that the strain occurring in SLs generally decreases with an increase of well/barrier thickness. Fitting of X-ray diffraction curves allowed determining the real thicknesses of the GaN wells and AlN barriers. Since blurring of the interfaces causes deviation of calculated data from experimental results the quality of the interfaces has been evaluated as well and compared with results of TEM measurements. For the samples with thinner wells/barriers the presence of pin-holes and threading dislocations has been observed in TEM measurements. The best quality of interfaces has been found for the sample with a well/barrier thickness of 3 nm. Finally, PL spectra showed that due to Quantum-Confined Stark Effect the PL peak energies of the SLs decreased with increasing the width of the GaN quantum wells and AlN barriers. The effect is well modelled by ab initio calculations based on the density functional theory applied for tetragonally strained structures of the same geometry using a full tensorial representation of the strain in the SLs.

cond-mat.mtrl-sci↗

arXiv2024

Polarization spontaneous and piezo: fundamentals and their implementation in ab initio calculations

Fundamental properties of spontaneous and piezo polarization are reformulated and critically reviewed. It was demonstrated that Landau definition of polarization as a dipole density could be used to the infinite systems. The difference between the bulk polarization and surface polarity are distinguished thus creating clear identification of both components. The local model of spontaneous polarization was created and used to calculate spontaneous polarization as the electric dipole density. It was shown that the proposed local model correctly predicts c-axis spontaneous polarization values of the nitride wurtzite semiconductors. It was also shown that the proposed model predicts zero polarization in the plane perpendicular to the c-axis, in accordance with symmetry requirements. In addition, the model results are in accordance with polarization equal to zero for zinc blende lattice. These data confirm the basic correctness of the proposed model. The spontaneous polarization values obtained for all wurtzite III nitrides (BN, AlN, GaN and InN) are in basic agreement with the earlier calculations using Berry phase and slab models of Bernardini et al. {Bernardini et al. Phys Rev B 56 (2001) R10024 & 63 (2001) 193201} but not with Dreyer et al. {Dreyer et al. Phys. Rev X 6 (2016) 021038}. Wurtzite nitride superlattices ab initio calculations were performed to derive polarization-induced fields in the coherently strained lattices showing good agreement with the polarization values. The strained superlattice data were used to determine the piezoelectric parameters of wurtzite nitrides obtaining the values that were in basic agreement with the earlier data. Zinc blende superlattices were also modeled using ab initio calculations showing results that are in agreement with the absence of polarization of all nitrides in zinc blende symmetry.

cond-mat.mtrl-sci↗

arXiv2024

Pressure-dependent bandgap study of MBE grown {CdO/MgO} short period SLs using diamond anvil cell

Semiconductor superlattices have found widespread applications in electronic industries. In this work, short-period superlattice structure (SLs) composed of CdO and MgO layers was grown using the plasma-assisted molecular beam epitaxy (PA-MBE) technique. The optical property of the SLs was investigated by absorption measurement at room temperature. The ambient-pressure direct bandgap was found to be 2.76 eV. The pressure dependence of fundamental bandgap has been studied using a diamond anvil cell (DAC) technique. It has been found that the band-to-band transition shifts toward higher energy with applied pressure. The bandgap of SLs was varied from 2.76 eV to 2.87 eV with applied pressure varied from 0 to 5.9 GPa. The pressure coefficient for the direct bandgap of SLs was found to be 26 meV/GPa. The obtained experimental result was supported by theoretical results obtained using DFT calculations. The volume deformation potential was estimated using the empirical rule. We believe our findings may provide valuable insight for a better understanding of {CdO/MgO} SLs towards their future applications in optoelectronics.

cond-mat.mtrl-sci↗

arXiv2024

Coulomb contribution to Shockley-Read-Hall (SRH) recombination

Defect-mediated nonradiative recombination, known as Shockley-Read-Hall (SRH) recombination is reformulated. The introduced model considers Coulomb attraction between charged deep defect and the approaching free carrier, showing that this effect may cause considerable increase of the carrier velocity approaching the recombination center. The effect considerably increases the carrier capture rates. It is demonstrated that in the typical semiconductor device or semiconductor medium, the SRH recombination cannot be neglected at low temperatures. The SRH is more effective in the case of low doped semiconductors. Effective screening by mobile carrier density could reduce the effect, leading to SRH rate increase.

cond-mat.mtrl-sci↗

arXiv2022

Polarization doping ab initio verification of the concept charge conservation and nonlocality

In this work, we study the emergence of polarization doping in AlxGa1-xN layers with graded composition from a theoretical viewpoint. We demonstrate that the charge conservation law applies for fixed and mobile charges separately, leading to nonlocal compensation phenomena involving bulk fixed and mobile charge and polarization sheet charge at the heterointerfaces. The magnitude of the effect allows obtaining technically viable mobile charge density for optoelectronic devices without impurity doping (donors or acceptors). Therefore, it provides an additional tool for the device designer, with the potential to attain high conductivities: high carrier concentrations can be obtained even in materials with high dopant ionization energies, and the mobility is not limited by scattering at ionized impurities.

cond-mat.mtrl-sci↗

arXiv2019

Spontaneous emission of color centers at 4eV in hexagonal boron nitride under hydrostatic pressure

The light emission properties of color centers emitting in 3.3-4 eV region are investigated for hydrostatic pressures ranging up to 5GPa at liquid helium temperature. The light emission energy decreases with pressure less sensitively than the bandgap. This behavior at variance from the shift of the bandgap is typical of deep traps. Interestingly, hydrostatic pressure reveals the existence of levels that vary differently under pressure (smaller increase of the emission wavelength compared to the rest of the levels in this energy region or even decrease of it) with pressure. This discovery enriches the physics of the color centers operating in the UV in hBN.

cond-mat.mtrl-sci↗

arXiv2019

Exact method of determination of the recombination mode from time resolved photoluminescence data

A method of data analysis is proposed for the determination of the carrier recombination processes in optically excited matter measured by time-resolved photoluminescence, differentiating monomolecular, bi-molecular, tri-molecular, and higher order molecular processes. Our method allows to determine whether the so-called ABC model describes time evolution of optical relaxation of the excited system. The procedure is applicable to the time evolution of any optically excited medium. As an illustration, the method is successfully applied to III-nitride polar and non-polar multi-quantum wells. We show that in this case the mono- and bi-molecular processes determine the carrier relaxation, and the tri-molecular Auger recombination contribution is negligible.

physics.optics↗