Low temperature pulsed electron deposition and characterization of ZnS films for application in solar cells

Abstract

Zinc Sulphide films were grown by pulsed electron deposition (PED) from room temperature to 350 °C to investigate the possibility of its application in solar cells, in particular as an alternative buffer layer deposited at low temperature. The films were characterized by X-ray diffraction, TEM, AFM, optical absorption and electrical measurements. ZnS films display crystalline structure and columnar growth at room temperature on amorphous substrate; the crystallization improves with the substrate temperature and is predominantly related to the cubic (111) orientation, while the thicker films show coexistence of hexagonal and cubic structures. All the samples have transparencies exceeding 70% in the range 400-1000 nm, energy band gap between 3.25 and 3.65 eV increasing with temperature and resistivity in the range of 10 4 -10 6 Ωcm. The optimization of the growth rate as a function of the growth parameters (substrate temperature and electron gun voltage) is also discussed. The reported results indicate that ZnS might be a suitable material for photovoltaic applications, specifically in process requiring low deposition temperature.

Pulsed laser deposition from ZnS and Cu2SnS3 multicomponent targets

“…The film quality appears to improve with substrate temperature up to 300 °C: with increasing temperature the optical band gap approaches that of the direct band gap of cubic-phase ZnS while the X-ray diffraction pattern indicates 8 an increasing crystalline fraction. These results are in close agreement with results from both pulsed laser deposition and pulsed electron deposition [5,21,23].…”

“…The observed peak positions are similar to observations using pulsed electron deposition by Zanettini et al [21]. This group investigated the same range of deposition temperatures using soda lime glass substrates and observed a similar structural modification from preferential cubic (220) growth direction at room temperature to cubic (111)-growth at higher temperature.…”

“…4a. The optical band gap of ZnS increases with the deposition temperature in a manner very similar to that observed by Zanettini et al [21] using pulsed electron deposition (inset in Fig. 4a).…”

“…On close comparison to the data of Zanettini et al [21], it is interesting to note that the highest optical band gap observed by Zanettini et al is slightly higher than that observed here, and is closer to the direct electronic band gap of hexagonal-phase ZnS, which is 3.67 eV. This may reflect a difference between pulsed laser and pulsed electron deposition, with a clearer transition to the hexagonal phase already at 300 °C with pulsed electron deposition.…”

“…ZnS has been deposited by a number of different methods including thermal evaporation [18,19], metal-organic chemical vapor deposition [20], and pulsed electron deposition [21] as well as PLD [5,11,22,23].…”