0000000000280662
AUTHOR
T. Barfels
Electron beam induced optical and electronical properties of SiO 2
Abstract Ionizing radiation in dielectric and optically transparent silica as well as thin SiO 2 layers produces defect luminescence as well as charge storage. A comparison of different excitation–relaxation processes like cathodoluminescence, charge injection and trapping, secondary electron field emission, and exoelectron emission leads to a generally similar excitation dose behaviour described by an electron beam saturation dose of 0.01–0.1 C/cm 2 . This suggests a correlation of these four electron excitation mechanisms likely related to the same kind of defect in glassy SiO 2 , the 2-fold-coordinated silicon Si: centre with typical electronic singlet–singlet and singlet–triplet transit…
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…
Radiation induced defects in SiO 2
The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) …
Structure and luminescence of GaN layers
Abstract GaN films grown on 〈1 1 1〉 Si substrate by means of low pressure MOCVD technique in a horizontal flow quartz reactor are characterized by different thin layer analysis methods. The polycrystalline hexagonal structure of the GaN layers has been checked by means of grazing incidence X-ray diffractometry and IR spectroscopy. Cathodoluminescence (CL) spectra and their time kinetics are studied. The mean decay time of the 3.44 eV UV bound exciton transition is below 1 ns, whereas the 3.26 eV violet band shows a slow hyperbolical decay over about 1 μs. A third yellow band appears at 2.12 eV due to transitions via localized states.
Cathodoluminescence of crystalline and amorphous SiO2 and GeO2
Abstract Cathodoluminescence (CL) and its temperature-dose behaviour are presented for different crystalline and amorphous modifications of SiO 2 and GeO 2 as well as for Ge-doped SiO 2 layers. The crystalline samples include four-fold coordinated Si and Ge in hexagonal quartz and quartz-like crystals, respectively, as well six-fold coordinated atoms in tetragonal rutile-like crystals. The detected luminescence bands, in general, are attributed to three optical active luminescence centres: the two-fold coordinated silicon (=Si:) and germanium (=Ge:) centre, respectively, the non-bridging oxygen hole centre (NBOHC) and the self trapped exciton (STE). The first ones, the oxygen deficient cent…
Defect Luminescence Study in Tetragonal GeO2 Crystals
The perovskite-or rutile-like GeO2 crystals were grown by the “top-seed” method from a fused germanium dioxide solution with sodium bicarbonate. The luminescence was studied under cathode-, x-ray, and photo-excitation. There are two luminescence bands at 550 nm and 400 nm with slow (100–200 µs) and fast (<20 ns) decay, respectively. The luminescence can be excited either by intra-center and electron-hole recombination processes. An analogous luminescence, however with strong non-exponential decay, is observed in glassy materials obtained from the frozen solution. Sodium-germanate glasses melted under oxygen deficient condition also possess similar luminescence, therefore the luminescence is…
Cathodoluminescence decay kinetics in Ge+, Si+, O+ implanted SiO2 layers
Abstract Cathodoluminescence spectral shapes and respective band decay times show no similarity between luminescence centers in different crystal and amorphous modifications of SiO2 and GeO2. On the other hand, the additionally produced red luminescence centers (650 nm) by oxygen implantation into SiO2 layers are of the same nature as in stoichiometric SiO2 and are attributed to the non-bridging oxygen hole center (NBOHC). On the other hand, the elevated blue luminescence (460 nm) in Si implanted SiO2 belongs to the silicon related oxygen deficient center (SiODC) as in stoichiometric layers also. Ge implantation into SiO2 and thermal post-annealing leads to a huge violet luminescence (400 n…
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…
Cathodoluminescence and IR absorption of oxygen deficient silica – influence of hydrogen treatment
Abstract The cathodoluminescence (CL) and IR absorption of silica samples with normal stoichiometry as well as with an extremely high level of oxygen deficit were studied. Additionally, some samples have been treated in hydrogen at 800°C. Crystalline quartz was used for reference measurements and the CL data have been compared with those of X-ray excited luminescence (XL). The luminescence spectra of silica have a band at 1.85 eV due to non-bridging oxygens and the two bands at 2.7 and 4.4 eV due to twofold-coordinated silicons. The energetic yield for CL is about 0.1%, for XL it approaches 0.15%. Cathodoluminescence of quartz at temperatures >130 K exhibits the self-trapped exciton lumines…