0000000000387951
AUTHOR
Andris Gulans
Luminescence and electron transport properties of GaN and AlN layers
Abstract The transport properties of free charge carriers, photo- and cathodo-luminescence (CV) in GaN and AlN films obtained by MOCVD technique on sapphire and Si substrates, are investigated. The concentration of free charge carriers in GaN is of order 10 17 – 10 19 cm −3 whereas AlN thin films are insulating. The Hall mobility of electrons are 80– 140 cm 2 / V s ). In undoped GaN films the spectral composition of CL is close to photoluminescence (PL) when excited in the region of band–band transitions. The decay time constant of the 3.44 eV UV emission attributed to the bound exciton is considerably less than 1 ns , whereas the 3.26 eV violet (VI) band shows a slow hyperbolical decay ove…
Ab initio calculations of charged point defects in GaN
The Generalized Gradient Approximation (GGA) of a Density Functional Theory (DFT) in LCAO basis is used to determine electronic structure of charged point defects in hexagonal GaN. Impurities of MgGa, ZnGa, SiN and CN (the most common dopants) were considered for charge states 0, ±1, –2. The vacancies of VGa and VN were considered for charge states 0 and 0, ±1, ±2 respectively. The defects in consideration are compared from the point of view of the one-electron states localization. All the calculations were performed for a supercell containing 96 atoms. The divergence due to periodically repeated charges has been eliminated by the use of a uniform background charge of an opposite sign. (© 2…
Ab initio calculation of wurtzite‐type GaN nanowires
Ab initio calculations of wurtzite-type GaN nanowires have been performed using density functional theory. Different shapes of nanowires of with similar diameters of around 2 nm have been considered to determine the stability of the structures. The quantitative similarities in the local properties obtained and dangling bond energies of nanowires and bulk surfaces have lead to a simple model model for a calculation of effective Young's modulus of nanowires of arbitrary diameters and shapes. The size dependence of the Young's modulus reveals a softening of GaN nanowires with the decrease of the diameter. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
EPR hyperfine structure of F‐type centres in pure LiBaF 3 crystal
We studied EPR spectra of pure LiBaF3 sample of high quality. For EPR measurements LiBaF3 sample was X-irradiated at room temperature, however spectra could be observed at low temperatures - at 77 K. All hyperfine structure lines of F-type centre could be well resolved contrary to our earlier studies of Fe doped LiBaF3 crystal. Qualitative analysis with g-tensor parameters derived from magneto-optical measurements showed that the F-type centre observed earlier by MCD-EPR techniques is the same F-type centre we observe with the EPR. We analyse origin of the hyperfine structure of the EPR spectra and their angular dependencies and discuss the structure of F-type centres in the LiBaF3 crystal.…
LCAO calculation of neutral defects in GaN
Four well known HF, LDA, GGA and B3LYP Hamiltonians in LCAO approximation have been used in band structure calculations to obtain the main properties of the perfect GaN crystal with hexagonal lattice (C space group). Calculated lattice parameters, elastic constants and the band gap have been compared with the experimental data and the results of other calculations. As a consequence, the GGA Hamiltonian has been chosen, giving the lattice parameters a = 3.20 A, c = 5.20 A, u = 0.377, the bulk modulus B = 206 GPa and the energy gap Eg = 2.7 eV. These results reasonably reproduce the experimental data. For the point defects calculation (VGa, VN, MgGa, ZnGa, CN, and SiN) the supercell model was…
Cathodoluminescence of Ge+, Si+, and O+ implanted SiO2 layers and the role of mobile oxygen in defect transformations
Abstract Thermally grown SiO 2 layers of thickness d =500 nm have been implanted by Ge + , Si + , and O + ions of energy 350, 150, and 100 keV, respectively, and a uniform implantation dose of D i =5×10 16 ions/cm 2 . Thus the implantation profiles are expected with a concentration maximum of nearly 4 at.% at the half-depth d m ≅250 nm of the SiO 2 layers. After thermal annealing to 900 °C for 1 h in dry nitrogen or vacuum the typical violet luminescence band ( λ =400 nm) of the Ge + implanted centers is increased more than 200-fold and the Ge luminescent center depth profile is shifted from about 250 to 170 nm towards the surface as determined by cathodoluminescence (CL) depth profiling. I…