Sanja Žonja

Investigations of the disorder in the TaxN thin films: On the first order Raman spectrum of the rock salt crystal structure

First order Raman absorption in materials with the rock salt crystal structure is forbidden. Its appearance in real crystals results from the presence of vacancies and other defects. For TaxN polycrystalline thin films, we found that imperfections that reduce the coherence length contribute to the appearance of the first order Raman spectrum. This investigation enables us to better understand the anomalous concentration dependence of the resistivity of TaxN polycrystalline thin films fabricated using reactive sputtering at 450 °C and 4.9 mTorr nitrogen pressures on amorphous substrates.

Low-temperature transport properties of TaxN thin films (0.72 ≤ x ≤ 0.83)

We report on low-temperature (4‐320K) transport properties of TaxN thin films deposited on an amorphous SiO2 substrate. In this work, TaxN thin films were restricted to a narrow range of x :0 .72 x 0.83 yet show considerable and nonmonotonic variation of their transport properties with Ta concentration. This behaviour is consistent with a local minimum in the density of electronic states at the Fermi level, as calculated for the rock salt intermetallic Ta4N5, and a rigid band model for describing the transport. The temperature dependence of the resistivity is best fit to the unusual form exp(− T/T 0). Interestingly enough, the fit parameter T0 correlates well with the temperature of the maximum of the corresponding thermopower. Both of these characteristics, the fit and the correlation with the thermopower, are consistent with the Jonson‐Mahan many-body formalism for charge and thermal transport when one has a nontrivial temperature dependence of the chemical potential. At the lowest temperatures measured, we have also found that the resistivity and thermopower show signatures of electron‐electron interactions. We discuss also our results in the light of some theories usually used for describing transport of thin films and to other experimental investigations that have been performed on TaxN.

Low temperature resistivity of heavily boron doped LPVCD polysilicon thin films

Heavily boron δ-doped polysilicon samples were prepared by horizontal low-pressure chemical vapour deposition (LPCVD) at 750 ◦ C for 1h and were annealed at 1200 ◦ C for 1h. In this way, the samples with low sheet resistance down to 8.9 � sq −1 , were obtained. The boron concentration was determined from the room temperature sheet resistance. The resistivity was measured from room temperatures down to 2K. A T 1/2 dependence of the conductivity in an unusually wide temperature interval, even up to 80K was observed. Above 140K, the resistivity can be described by the T 3/2 dependence. The experimental results were analysed within the theories for the disordered metals and compared with the corresponding existing resistivity data.

Grain growth from amorphous phase

Time dependence of the grain growth in phosphorus doped silicon thin films deposited in situ at 530 °C was investigated. The samples were annealed at 950 °C in different time intervals. The theories, which give the tn time dependent increase of grain size, cannot fit the observed data. We derived a differential equation which describes the grain growth from amorphous phase. Our experimental results and the solution of the differential equation show the effect of grain growth stagnation and even grain growth stop. The solution also comprises all the features of the result of the Monte Carlo simulation of the grain growth of pure materials.