Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment

Shafiul Monir,Dan Lamb,Xiaogang Yang,Stuart J C Irvine,Yuriy Vagapov,Giray Kartopu,Vincent Barrioz

doi:10.3390/app10051734

Abstract

The deposition of thin Cadmium Telluride (CdTe) layers was performed by a chamberless metalorganic chemical vapour deposition process, and trends in growth rates were compared with computational fluid dynamics numerical modelling. Dimethylcadmium and diisopropyltelluride were used as the reactants, released from a recently developed coating head orientated above the glass substrate (of area 15 × 15 cm2). Depositions were performed in static mode and dynamic mode (i.e., over a moving substrate). The deposited CdTe film weights were compared against the calculated theoretical value of the molar supply of the precursors, in order to estimate material utilisation. The numerical simulation gave insight into the effect that the exhaust’s restricted flow orifice configuration had on the deposition uniformity observed in the static experiments. It was shown that > 59% of material utilisation could be achieved under favourable deposition conditions. The activation energy determined from the Arrhenius plot of growth rate was ~ 60 kJ/mol and was in good agreement with previously reported CdTe growth using metalorganic chemical vapour deposition (MOCVD). Process requirements for using a chamberless environment for the inline deposition of compound semiconductor layers were presented.

Highlights

The growth rate of thin-film Cadmium Telluride (CdTe) using metalorganic chemical vapour deposition (MOCVD) has been found to be sensitive to both substrate temperature and reactant partial pressures [1], presenting a complex transport and kinetic process
This paper focused on two aspects of our chamberless inline MOCVD process: (1) the influence and optimisation of the exhaust restricted flow orifice (RFO) configuration, related to the deposition profile in static mode, and (2) the effects of key deposition parameters on the pyrolysis of CdTe in the dynamic mode, including substrate temperature (Ts ), precursor concentration (Pcon ) and total gas flow (Ftotal )
The experiments were carried out using a chamberless inline system, incorporating 6 individual coating heads capable of depositing different materials by MOCVD [17]

Summary

Introduction

The growth rate of thin-film Cadmium Telluride (CdTe) using metalorganic chemical vapour deposition (MOCVD) has been found to be sensitive to both substrate temperature and reactant partial pressures [1], presenting a complex transport and kinetic process. CdTe and another group II-VI compound semiconductor thin films [5,6] It has been conventionally associated with a low-pressure batch process for the fabrication of optoelectronic devices [7], including multi-junction III-V photovoltaic cells for space applications [8]. In a precursor to the work reported in this paper, Yang et al [16] conducted three-dimensional (3D) simulations using CFD code – Fluent, investigating the effects of various conditions on CdTe film growth in an inline MOCVD reactor, where precursor gas flows were delivered normally to the direction of substrate translation. The deposition profiles, measured film thicknesses and material (chemical precursor) utilisation were correlated to CFD simulations

Experimental Section

Numerical Modelling

Static Mode – Deposition Profile

Path injector near RFO-A

5.5.Conclusions