Electrochemical aspects of the formation of Bi 2Te 3 thin film via the route of ECALE

Abstract

A Bi 2Te 3 VA–VIA group compound thin film was prepared via the route of electrochemical atomic layer epitaxy in this paper. The dependence of thin film formation on the electrochemical conditions (such as deposition potential control, supporting electrolyte and substrate) was studied, and the formation process of Bi 2Te 3 film was determined. The results show that Bi upd on Pt occurs at more negative potential in a HNO 3 supporting electrolyte than in a HClO 4 supporting electrolyte, and the Te upd peak moves to a more negative potential in HClO 4 supporting electrolyte solution than that in HNO 3 solution; Both Te and Bi upd on an Ag substrate occur at more negative potentials than that on a Pt substrate. In order to reach steady state deposition, a potential adjustment is necessary for the first 30 or more cycles of each component. After deposition of this initial ‘buffer layer’, the potentials can be kept constant for the remaining cycles. The effect of the slope of the shift of potential used to deposit the first 30 atomic layers of Bi and Te on the deposit has also been investigated. The deposit exhibits a two phase mixture of excess elemental Bi and Bi 2Te 3 compound when the slope is larger than −4 mV/p (p indicates per cycle); a single-phase Bi 2Te 3 compound was obtained at a slope of −6 mV/p, and Bi 4Te 3 compound also appears in the deposit along with Bi 2Te 3 when the slope is decreased to a more negative value of −10 mV/p.