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Various routes for low temperature RFmagnetron sputtering of Indium Tin Oxide films

Publication . Sousa, M. G.; Cunha, A. F. da; Fernandes, P. A.

In this work we have studied the influence of the Ar working pressure, substrate temperature, low power plasma irradiation and partial pressure of hydrogen in the RF-magnetron sputtering of indium tin oxide (ITO) thin films on glass substrates. This work aims at identifying the best conditions to achieve good quality ITO film at low temperature. Four sets of samples were prepared which were characterized by scanning electron microscopy, X-ray diffraction (XRD), Van der Pauw, transmittance and absorbance measurements

2014Conference object

Open access

Growth and Characterization of SnSe2 by selenization of sputtered metallic precursors

Publication . Fernandes, P. A.; Sousa, M. G.; Salomé, P. M. P.; Teixeira, J. P.; Leitão, J. P.; Cunha, A. F. da

In the present work, we present a process to grow tin diselenide thin films by selenization at a maximum temperature of 470 ºC, of tin metallic precursor layers deposited by dc magnetron sputtering. For this maximum temperature, disklike grain morphologies were observed. Prominent XRD reflections at 2θ= 30.75º, 40.10º and 47.72º and vibration modes located at 119 cm-1 and 185 cm-1 were observed. These results allowed concluding that the dominant phase is SnSe2. The composition analysis, done by energy dispersive spectroscopy (EDS), showed that the films were close to being stoichiometric SnSe2 with a Se to Sn ratio of 1.95. Photoluminescence characterization was performed and revealed a dominant band at 0.874 eV and two other bands at ~0.74 and 1.08 eV with a lower relative intensities. The observed radiative transitions depend critically on the temperature.

2014Conference object

Open access

Annealing of RF-magnetron sputtered SnS2 precursors as a new route for single phase SnS thin films

Publication . Sousa, M. G.; Cunha, A. F.; Fernandes, P. A.

Tin sulphide thin films have been grown on soda-lime glass substrates through the anneali ng of RF-mag netron sputtered SnS2 precursors . Three different approaches to the annealing were compared and the resulti ng films thoroughly studied. One series of precursors was annealed in a tubular furnace directly exposed to a flux of sulphur vapour plus formi ng gas, N 2 + 5%H2, and at a constant pressure of 500 mbar. The other two series of identical precursors were annealed in the same furnace but inside a graphite box with and without elemental sulphur evaporation again i n the presence of N 2 + 5%H2 and at the same pres sure as for the sulphur flux experiments. Different maximum annealing temperatures for each set of sam ples , in the range of 300-570 °c,were tested to study their effects on the properties of the final films.The resulti ng phases were structurally investigated by X-Ray Diffraction (XRD) and Raman spectroscopy. Annealing of SnS2 precursors in sulphur flux produced films where SnS2 was dominant for temperatures up to 480 °C. Increasing the temperature to 530 °c and 570 °c led to films where the dominant phase became Sn2S3• Annealing of SnS2 precursors in a graphite box with sulphur vapour at temperatures in the range between 300 °c and 480 °c the films are multi-phase , containing Sn2 S3, SnS2 and SnS. For high annealing temperatures of 530 °c and 570 °c the films have SnS as the dominant phase.Annealing of SnS2 precursors in a graphite box without sulphur vapour at 300 °c and 360 °c the films are essentially amor phous, at 420 °c SnS2 is the dominant phase. For temperatures of 480 °c and 530 °c SnS is the dominant phase but also same residual SnS2 and Sn2S3 phases are observed. For annealing at 570 °c, according to the XRD results the films appear to be single phase SnS. The composition was studied usi ng energy dis persive spectroscopy being then correlated with the annealing temperature. Scanning electron micros copy studies revealed that the SnS films exhibit small grain structure and the film surface is rough. Optical measurements were performed, from which the band gap energies were estimated .These studies show that the direct absorption transitions of SnS are at 1.68 eV and 1.41 eV for annealing in graphite box with and without elemental sulphur evaporation, respectively . For the indirect transition the val ues var ied from 1.49 eV to 1.37 eV.The results of this work show that the third approach is better suited to pro duce single phase SnS films. However, a finer tunning of the duration of the high temperature plateau of the anneali ng profile is required in order to eliminate the -Sn top layer.

2014Journal article

Open access

On the properties of Cu2ZnSn(S,Se)4 thin ﬁlms prepared by selenization of binary precursors using rapid thermal processing

Publication . Menon, M R Rajesh; Ranjbar, Samaneh; Sousa, M G; Fernandes, P A; Cunha, A F da

Cu2ZnSn(S,Se)4 thin ﬁlms were grown on molybdenum coated glass substrates by selenization of stacked precursor layers of zinc, tin disulﬁde and copper sulﬁde. Selenization was performed using a rapid thermal processor at maximum temperatures in the range of 400°C to 550°C and at heating rates of 1°C/s and 2°C/s. The compositional, morphological and structural characterization of the ﬁlms was carried out using energy dispersive x-ray spectroscopy, scanning electron microscopy, x-ray diffraction and Raman spectroscopy. X-ray diffraction and Raman scattering analysis suggests the formation of Cu2ZnSn(S,Se)4 only at lower temperatures, whereas Cu2ZnSnSe4 was formed at higher temperatures regardless of the heating rate used. Compositional analysis revealed that the ﬁlms were Zn-poor and Sn-rich. However, the samples approach a near stoichiometric composition due to the loss of tin at a selenization temperature and heating rate of 550°C and 2°C/s, respectively. Large grains with an average lateral dimension of 4.5μm were observed for ﬁlms prepared at these conditions which are very desirable for an absorber for solar cells.

2014Journal article

Open access

Growth and Characterization of single phase SnS thin films by sulphurization of sputtered sulphide precursors

Publication . Sousa, M. G.; Cunha, A. F. da; Fernandes, P. A.

Single-phase SnS thin films have been grown on soda-lime glass substrates based on the sulphurization of RF-magnetron sputtered SnS2 precursors. Two different approaches to sulphurization were compared and thoroughly studied. The two series of identical precursors were sulphurized in the same furnace, inside a graphite box with and without elemental sulphur evaporation. Different maximum sulphurization temperatures, in the range 300ºC to 570ºC, were tested. Sulphurization of SnS2 precursors in a graphite box with and without sulpur vapour at high temperature produces SnS films which appear to be single-phase from the structural analysis. The studies show that the direct absorption transitions of SnS are at 1.41 eV and 1.68 eV for sulphurization in graphite box with and without elemental sulphur evaporation, respectively. The indirect absorption transition values varied from 1.49 eV e 1.37 eV.

2014Conference object

Open access