Abstract
Cadmium Sulphide (CdS) is an important n-type semiconductor widely used as a window layer in thin film photovoltaics Copper Indium Selenide, Copper Indium Gallium (di)Selenide, Copper Zinc Tin Sulphide and Cadmium Telluride (CdTe). Cadmium Sulphide has been deposited using a number of techniques but these techniques can be slow (chemical bath deposition and Radio Frequency sputtering) or the uniformity and the control of thickness can be relatively difficult (close space sublimation). In this paper we report on the development of a process using pulsed Direct Current magnetron sputtering which allows nanometre control of thin film thickness using time only. The CdS thin films deposited in this process are highly uniform and smooth. They exhibit the preferred hexagonal structure at room temperature deposition and they have excellent optical properties. Importantly, the process is highly stable despite the use of a semi-insulating magnetron target. Moreover, the process is very fast. The deposition rate using 1.5kW of power to a 6-inch circular magnetron was measured to be greater than 8nm/s. This makes the process suitable for industrial deployment.
Highlights
Cadmium Sulphide (CdS) is an important semiconductor material widely used in thin film photovoltaics as a window layer [1,2]
Thin film CdS has been used as a n-type material to form a heterojunction in a number of photovoltaic systems including copper indium selenide (CIS) [7], copper indium galliumselenide (CIGS) [8,9,10], copper zinc tin sulphide (CZTS) [11,12] and cadmium telluride (CdTe) [1,13,14,15,16]
The X-ray Photoelectron Spectroscopy (XPS) analysis of CdS films deposited at different values of Ar gas flow, deposition power and temperature showed that the chemical composition of the sputtered film CdS was unaffected by the deposition parameters
Summary
Cadmium Sulphide (CdS) is an important semiconductor material widely used in thin film photovoltaics as a window layer [1,2]. Thin film CdS has been used as a n-type material to form a heterojunction in a number of photovoltaic systems including copper indium selenide (CIS) [7], copper indium gallium (di)selenide (CIGS) [8,9,10], copper zinc tin sulphide (CZTS) [11,12] and cadmium telluride (CdTe) [1,13,14,15,16]. The major advantage is that the process produces high deposition rates suitable for use in solar module manufacturing These rates are over an order of magnitude faster than those obtained by RF sputtering. In common with other applications we find that the energetics of the pulsed DC process produce favourable thin film properties and the power supply configuration avoids the need for matching circuits [26,27]
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