Carrier transport in polycrystalline ITO and ZnO Al II The Influence of grain barriers and boundaries

ITO and ZnO Al films have been deposited by magnetron sputtering from ceramic and metallic targets at different substrate temperatures and with different plasma excitation modes DC and RF 13.56 and 27.12 MHz . Temperature dependent conductivity and Hall measurements down to 50 K were used to determine the carrier concentrations ND and the Hall mobilities . From the ND dependences, which were fitted by a carrier transport model taking into account ionized impurity and grain barrier scattering, the trap densities at the grain boundaries were estimated. ITO films show much lower trap densities down to Nt amp; 8776;1.5.1012 cm 2, compared to Nt values up to 3.1013 cm 2 for ZnO Al films. The temperature dependent mobilities were fitted by a phenomenological model with a T independent term and a metal like contribution or a thermally activated part due to grain barrier limited transport. Seebeck coefficient measurements as a function of the carrier concentration give hints to different transport mechanisms in ITO and ZnO

Carrier transport in polycrystalline transparent conductive oxides A comparative study of zinc oxide and indium oxide

Highly doped indium tin oxide films exhibit resistivities ? as low as 1.2.10 4 ?cm, while for ZnO films resistivities in the range of 2 to 4.10 4 ?cm are reported. This difference is unexpected, if ionized impurity scattering would be dominant for carrier concentrations above 1020 cm 3. By comparing the dependences of the effective Hall mobility on the carrier concentration of ZnO and ITO it is found that grain barriers limit the carrier mobility in ZnO for carrier concentrations as high as 2.1020 cm 3, independently, if the films were grown on amorphous or single crystalline substrates. Depending on the deposition method, grain barrier trap densities between 1012 to 3.1013 cm 2 were estimated for ZnO layers. Also, crystallographic defects seem to reduce the mobility for highly doped ZnO films. On the other hand, for ITO films such an influence of the grain barriers was not observed down to carrier concentrations of about 1018 cm 3. Thus the grain barrier trap densities of ZnO and ITO are significantly different, which seems to be connected with the defect chemistry of the two oxides and especially with the piezoelectricity of zinc oxid

Photoactive Tungsten Disulfide WS2 Nanosheets, Prepared by Rapid Crystallization from Liquid Sulfides

We have shown, that photoactive, highly 001 textured tungsten disulfide WS2 films can be prepared both on insulating as well as metallic substrates. The WS2 films are crystallized from X ray amorphous WS3 x films by a rapid annealing process in an H2S atmosphere with the assistance of metal sulfide droplets, which are formed, when the eutectic temperature in the system metal sulfur is exceeded. As promoters Ni, Co and Pd can be used, where the eutectic temperatures with sulfur are in the range from 620 to 680 C. From ex situ and in situ analysis a modified model for the formation of the WS2 nanosheets was derived, which resembles the well known VLS vaporliquid solid model for the formation of nanorods or whiskers , except that in our systems the precursor is also an amorphous solid, and instead of 1 dimensional rods, 2 dimensional nanosheets are grown. Especially, the preparation on metallic layers W, TiN , which was not successful before, offers now the opportunity, to prepare thin film solar cells from these WS2 films. First experiments to prepare thin film solar cells show, that short circuits occur, most probably at grain boundaries, which have to be avoided or passivate

Optical and electronic properties of CrOxNy films, deposited by reactive DC magnetron sputtering in Ar N2 O2 N2O atmospheres

Chromium oxynitride films CrOxNy were prepared by reactive magnetron sputtering from a chromium target in Ar O2 N2O N2 gas mixtures. The argon to nitrogen partial pressure ratio and the DC discharge power were kept constant in the experiments. By changing the gas composition the film stoichiometry can be continuously varied from CrN to Cr2O3. The film composition has been determined by Rutherford backscattering RBS and by elastic recoil detection analysis ERDA . From an XRD analysis it was concluded that the films consist of CrN nanocrystals in an amorphous oxide matrix. Depending on the oxygen content [O], the electronic behaviour of the films changes from metallic [O] ? 0 to semiconducting [O] gt; 0.5 , accompanied by the evolution of an optical band gap, which was determined by spectral transmission and reflection measurements. The negative temperature coefficient at ? 300 K of the resistivity of the films is in the range of 0.5 CrN to 2 K 1 CrO1.6 . This film property can be used for temperature dependent resistors, for instance in thermal radiation detector

Metal sulfide assisted rapid crystallization of highly 001 textured tungsten disulphide WS2 films on metallic back contacts

Highly 001 textured, photoactive WS2 films, which could be deposited before only on insulating substrates, have been prepared on polycrystalline metal layers, which can be used as back contacts for electronic WS2 devices, for instance for thin film solar cells. The WS2 films were prepared by the amorphous solid liquid crystalline solid aSLcS crystallization process from a Ni S eutectic. However, normal polycrystalline metallic films can not be used as back contact layers, caused by the diffusion of the thin metal promoter Ni into the back contact layer, before a nickel sulfur eutectic can be formed. Preventing the diffusion of the metal promoter into the back contact allows using the well known metal promoter assisted crystallization to grow photoactive films on different back contacts, like TiN O. Additionally, WS2 films on tungsten layers could be grown by Ni induced sulfidation of W films. Based on these experiments the model of the rapid nickel sulfide induced crystallization was modified Ni assists the growth of WS2 crystallites already at temperatures between 500 and 600 amp; 8201; C leading to WS2 films with differently oriented crystallites. At temperatures above the Ni S eutectic temperature 637 amp; 8201; C liquid NiSx droplets induce, as reported earlier, a rapid recrystallization, which leads to WS2 films with strong 001 orientatio