Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userKinetics of charge carrier recombination in beta-Ga2O3 crystals
68
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Cathodoluminescence spectra were measured to determine the characteristics of luminescence bands and carrier dynamics in beta-Ga2O3 bulk single crystals. The CL emission was found to be dominated by a broad UV emission peaked at 3.40 eV, which exhibits strong quenching with increasing temperature; however, its spectral shape and energy position remain virtually unchanged. We observed a super-linear increase of CL intensity with excitation density; this kinetics of carrier recombination can be explained in terms of carrier trapping and charge transfer at Fe impurity centres. The temperature-dependent properties of this UV band are consistent with weakly bound electrons in self-trapped excitons with an activation energy of 48 +/- 10 meV. In addition to the self-trapped exciton emission, a blue luminescence (BL) band is shown to be related to a donor-like defect, which increases significantly in concentration after hydrogen plasma annealing. The point defect responsible for the BL, likely an oxygen vacancy, is strongly coupled to the lattice exhibiting a Huang-Rhys factor of ~ 7.3.
rate research
Read More
The kinetics of the charge carrier recombination in dye molecule-doped multilayer organic light-emitting diodes (OLEDs) was quantified by transient electroluminescence (EL). Three sets of dye molecules, such as derivatives of naphthalimide and stilbene, were used as dopants in light-emission layer. Although the devices show almost the same EL spectra for each set of molecules, they show very different EL efficiency. The difference in EL efficiency was attributed to the difference in charge carrier recombination, as revealed by transient EL. The recombination coefficient ({gamma}) was determined from the long-time component of the temporal decay of the EL intensity after a rectangular voltage pulse was turned off. It was found that {gamma} and EL efficiency were both strongly dependent on the molecular structures of the dopants, and the donor groups and {pi}-conjugated structure guaranteed high {gamma} and EL efficiency in OLEDs.
We have applied the photoexcited muon spin spectroscopy technique (photo-$mu$SR) to intrinsic germanium with the goal of developing a new method for characterizing excess carrier kinetics in a wide range of semiconductors. Muon spin relaxation rates can be a unique measure of excess carrier density and utilized to investigate carrier dynamics. The obtained carrier lifetime spectrum can be modeled with a simple diffusion equation to determine bulk recombination lifetime and carrier mobility. Temperature dependent studies of these parameters can reveal the recombination and diffusion mechanism.
We derive a dielectric function tensor model approach to render the optical response of monoclinic and triclinic symmetry materials with multiple uncoupled infrared and farinfrared active modes. We apply our model approach to monoclinic $beta$-Ga$_2$O$_3$ single crystal samples. Surfaces cut under different angles from a bulk crystal, (010) and ($bar{2}$01), are investigated by generalized spectroscopic ellipsometry within infrared and farinfrared spectral regions. We determine the frequency dependence of 4 independent $beta$-Ga$_2$O$_3$ Cartesian dielectric function tensor elements by matching large sets of experimental data using a point by point data inversion approach. From matching our monoclinic model to the obtained 4 dielectric function tensor components, we determine all infared and farinfrared active transverse optic phonon modes with $A_u$ and $B_u$ symmetry, and their eigenvectors within the monoclinic lattice. We find excellent agreement between our model results and results of density functional theory calculations. We derive and discuss the frequencies of longitudinal optical phonons in $beta$-Ga$_2$O$_3$. We derive and report density and anisotropic mobility parameters of the free charge carriers within the tin doped crystals. We discuss the occurrence of longitudinal phonon plasmon coupled modes in $beta$-Ga$_2$O$_3$ and provide their frequencies and eigenvectors. We also discuss and present monoclinic dielectric constants for static electric fields and frequencies above the reststrahlen range, and we provide a generalization of the Lyddane-Sachs-Teller relation for monoclinic lattices with infrared and farinfrared active modes. We find that the generalized Lyddane-Sachs-Teller relation is fulfilled excellently for $beta$-Ga$_2$O$_3$.
The effects of hydrogen incorporation into beta-Ga2O3 thin films have been investigated by chemical, electrical and optical characterization techniques. Hydrogen incorporation was achieved by remote plasma doping without any structural alterations of the film; however, X-ray photoemission reveals major changes in the oxygen chemical environment. Depth-resolved cathodoluminescence (CL) reveals that the near-surface region of the H-doped Ga2O3 film exhibits a distinct red luminescence (RL) band at 1.9 eV. The emergence of the H-related RL band is accompanied by an enhancement in the electrical conductivity of the film by an order of magnitude. Temperature-resolved CL points to the formation of abundant H-related donors with a binding energy of 28 +/- 4 meV. The RL emission is attributed to shallow donor-deep acceptor pair recombination, where the acceptor is a VGa-H complex and the shallow donor is interstitial H. The binding energy of the VGa-H complex, based on our experimental considerations, is consistent with the computational results by Varley et al [J. Phys.: Condens. Matter, 23, 334212, 2011].
Performing deep level transient spectroscopy (DLTS) on Schottky diodes, we investigated defect levels below the conduction band minima (Ec) in Czochralski (CZ) grown unintentionally-doped (UID) and vertical gradient freeze (VGF)-grown Zr-doped beta-Ga2O3 crystals. In UID crystals with an electron concentration of 10^17 cm-3, we observe levels at 0.18 eV and 0.46 eV in addition to the previously reported 0.86 (E2) and 1.03 eV (E3) levels. For 10^18 cm-3 Zr-doped Ga2O3, signatures at 0.30 eV (E15) and 0.71 eV (E16) are present. For the highest Zr doping of 5*10^18 cm-3, we observe only one signature at 0.59 eV. Electric field-enhanced emission rates are demonstrated via increasing the reverse bias during measurement. The 0.86 eV signature in the UID sample displays phonon-assisted tunneling enhanced thermal emission and is consistent with the widely reported E2 (FeGa) defect. The 0.71 eV (E16) signature in the lower-Zr-doped crystal also exhibits phonon-assisted tunneling emission enhancement. Taking into account that the high doping in the Zr-doped diodes also increases the electric field, we propose that the 0.59 eV signature in the highest Zr-doped sample likely corresponds to the 0.71 eV signature in lower-doped samples. Our analysis highlights the importance of testing for and reporting on field-enhanced emission especially the electric field present during DLTS and other characterization experiments on beta-Ga2O3 along with the standard emission energy, cross-section, and lambda-corrected trap density. This is important because of the intended use of beta-Ga2O3 in high-field devices and the many orders of magnitude of possible doping.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
