Edouard Monakhov

Lithium and electrical properties of ZnO

Hydrothermal grown n-type ZnO samples have been investigated by deep level transient spectroscopy (DLTS), thermal admittance spectroscopy (TAS), temperature dependent Hall effect (TDH) measurements, and secondary ion mass spectrometry (SIMS) after thermal treatments up to 1500 °C, in order to study the electrical properties of samples with different lithium content. The SIMS results showed that the most pronounced impurities were Li, Al, Si, Mg, Ni, and Fe with concentrations up to ∼5×1017 cm−3. The Li concentration was reduced from ∼1017 cm−3 in as-grown samples to ∼1015 cm−3 for samples treated at 1500 °C, while the concentration of all the other major impurities appeared stable. The results from DLTS and TAS displayed at least five different levels having energy positions of Ec−20 meV, Ec−55 meV, Ec−0.22 eV, Ec−0.30 eV, and Ec−0.57 eV (Ec denotes the conduction band edge), where the Ec−55 meV level is the dominant freeze out level for conduction electrons in samples treated at temperatures <1300 °C, wh...

Elemental distribution and oxygen deficiency of magnetron sputtered indium tin oxide films

The atomic structure and composition of noninterfacial ITO and ITO-Si interfaces were studied with transmission electron microscopy and x-ray photoelectron spectroscopy (XPS). The films were deposited by dc magnetron sputtering on monocrystalline p-type (100) Si wafers. Both as deposited and heat treated films consisted of crystalline ITO. The ITO/Si interface showed a more complicated composition. A thin layer of SiOx was found at the ITO/Si interface together with In and Sn nanoclusters, as well as highly oxygen deficient regions, as observed by XPS. High energy electron exposure of this area crystallized the In nanoclusters and at the same time increased the SiOx interface layer thickness.

Defect energy levels in hydrogen-implanted and electron-irradiated n -type 4H silicon carbide

Using deep level transient spectroscopy (DLTS), we have studied the energy position and thermal stability of deep levels in nitrogen doped 4H-SiC epitaxial layers after 1.2 MeV proton implantation ...

Evidence for Two Charge States of the S-Center in Ion-Implanted 4H-SiC

Proton-implanted 4H-SiC samples of n-type, have been investigated using Deep Level Transient Spectroscopy (DLTS). Two levels, referred to as S 1 and S2 have been studied in detail. S 1 and S2 are located, respectively, at 0.41 eV and 0.71 eV below the conduction band edg e. Their extrapolated capture cross-sections are both ∼5x10cm. Furthermore, isochronal annealing performed between 350 and 625K have shown a close one-to-one correlation betwee n the concentration of the two levels. Our results suggest strongly that these levels represent two charge states of the S-center, and the absence of a Pool-Frenkel effect indicates a cent r of acceptor type.

Defects in virgin hydrothermally grown n-type ZnO studied by temperature dependent Hall effect measurements

Temperature dependent Hall (TDH) effect measurements have been performed on three virgin and hydrothermally grown ZnO samples with resistivities between ∼5 and ∼200 Ω cm at room temperature. The electrical conduction observed experimentally in the temperature range of 330–70 K can be accurately described by three donor levels with positions 41–48, 60–66, and ∼300 meV below the conduction band edge (EC) and an acceptor level in the lower part of the energy band gap (EG). Correlation of the TDH data with results from secondary ion mass spectrometry and admittance spectroscopy on the same samples suggests a rather firm association of the intermediate donor level with complexes involving Al impurities, while the shallowest one is tentatively ascribed to H-related centers. A large fraction of the deep donor remains nonionized in the temperature range studied and contributes substantially to the neutral-impurity-scattering of the conducting electrons. A detailed analysis of the TDH data, using the relaxation ti...

Acceptor-like deep level defects in ion-implanted ZnO

This work was supported by the Norwegian Research Council through the Frienergi program and the Australian Research Council through the Discovery projects program.

Defect formation and thermal stability of H in high dose H implanted ZnO

implantation is found to create deformed layers with a uniaxial strain of 0.5–2.4% along the c-axis in ZnO, for the low and high dose, respectively. About 0.2–0.4% of the original implanted H concentration can still be detected in the samples by secondary ion mass spectrometry after annealing at a temperature up to 800 � C. The thermally stable H is tentatively attributed to H related defect complexes involving the substitutional H that are bound to O vacancies and/or the highly mobile interstitial H that are bound to substitutional Li occupying Zn vacancies as the samples are cooled slowly from high temperature annealing. H implantation to a dose of 1 � 10 17 cm � 2 and followed by annealing at 800 � C, is found to result in the formation of vacancy clusters that evolved into faceted voids with diameter varying from 2 to 30 nm. The truncations around the voids form more favorably on the O-terminated surface than on the Zn-terminated surface, suggesting that O is a preferred surface polarity for the internal facets of the voids in the presence of H. V C 2013 AIP Publishing LLC.

Optical activity and defect/dopant evolution in ZnO implanted with Er

The effects of annealing on the optical properties and defect/dopant evolution in wurtzite (0001) ZnO single crystals implanted with Er ions are studied using a combination of Rutherford backscattering/channeling spectrometry and photoluminescence measurements. The results suggest a lattice recovery behavior dependent on ion dose and involving formation/evolution of an anomalous multipeak defect distribution, thermal stability of optically active Er complexes, and Er outdiffusion. An intermediate defect band occurring between the surface and ion-induced defects in the bulk is stable up to 900 °C and has a photoluminescence signature around 420 nm well corresponding to Zn interstitials. The optical activity of the Er atoms reaches a maximum after annealing at 700 °C but is not directly associated to the ideal Zn site configuration, since the Er substitutional fraction is maximal already in the as-implanted state. In its turn, annealing at temperatures above 700 °C leads to dissociation of the optically active Er complexes with subsequent outdiffusion of Er accompanied by the efficient lattice recovery.

Phosphorus in-diffusion from a surface source by millisecond flash lamp annealing for shallow emitter solar cells

We have investigated in-diffusion of phosphorus into monocrystalline silicon by depositing a phosphorus source on the surface followed by millisecond flash lamp annealing (FLA) to form shallow emitters for solar cells. By varying both the energy density of a 20 ms flash in the range from 62 to 132 J/cm2 and the sample preheating, it is observed that FLA treatments can in-diffuse a high concentration of phosphorus atoms becoming electrically active. The most promising emitters are obtained after FLA in the energy range from 110 to 128 J/cm2 including preheating at 300 °C with a peak concentration of 4−6×1020cm−3. The emitter junction depth for these treatments is in the range of 100 nm to 200 nm, respectively.

Carrier Removal in Electron Irradiated 4H and 6H SiC

A strong reduction of the free carrier concentration has been observed in both 4H and 6H n-type SiC as a result of MeV-electron irradiation. Samples irradiated with a sufficiently high dose experience complete compensation of carriers. Irradiation with even higher doses reveals the same result, i.e. no conversion to p-type which occurs in silicon irradiated with high doses has been found. The dose required for complete loss of carrier response is higher for 6H than 4H material. Furthermore, the free carrier concentration depends on both measurement temperature and frequency and recovers after annealing. The results strongly suggest that deep acceptor levels in the upper half of the band gap are the main cause for the removal of free carriers rather than deactivation of the nitrogen donors as found in ion-irradiated samples, which is in agreement with previous findings on proton-irradiated 4H- and 6H-SiC[8].