# Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment
## 2 Experimental Section  
The experiments were carried out using a chamberless inline system, incorporating 6 individual coating heads capable of depositing different materials by MOCVD [17]. A single coating head on this system was used to deposit the CdTe layers reported in this work. Precursor gas flows were released from the coating head normal to the glass substrate being deposited on. The coating head consists of a precursor delivery system, surrounded by containment curtain flows (CCF) and a balanced flow exhaust system, which is pressure and flow controlled by a combination of regulated extraction and individual RFOs positioned around the deposition zone of the coating head [15]. Figure 1 shows a projection view of these components in the plane of substrate deposition, along with Figure 2 showing the over-layer grid system used for the analysis of deposition characteristics in static and dynamic modes. The chemical precursors used were dimethylcadmium (DMCd) and diisopropyltelluride (DIPTe) for cadmium (Cd) and tellurium (Te), respectively. High purity hydrogen (H\({}_{2}\)) gas (99.995%) was used for the main carrier gas, and nitrogen (N\({}_{2}\)) gas (99.9995%) was used for CCF. The heated stage was motion controlled and able to be positioned under any 1 of the 6 coating heads. Heating was achieved through infrared quartz elements radiating toward a graphite susceptor upon which the glass sample was mounted. The stainless steel surface temperatures of the coating head and the heated stage were maintained at 20-30 \({}^{\circ}\)C by using a closed-loop water cooling system. The temperature on the substrate's surface corresponded to the average surface temperature measured during temperature calibration (Figure 3). The set-point temperature from the controller was compared with the averaged measured substrate surface temperature (from 3 different areas) and was within \(\pm\)10 \({}^{\circ}\)C over a 15 \(\times\) 15 cm\({}^{2}\) area centrally located on the heated zone. Figure 1: Schematic representation of the coating head components [15]. The dashed edges (**a–d**) represent the containment curtain flows (CCF), the single solid line represents the precursor delivery, the dark solid grey shaded line represents the flow guide plate, the hashed square represents the active exhaust, surrounding the deposition area, and the black dots (RFO-A and RFO-B) represent the extraction points. The discontinuous light grey band represents the substrate width, while the central arrow indicates the direction of travel [17]. RFO: restricted flow orifice. Reproduced with permission from MOCVD for solar cells, a transition towards a chamberless inline process; published by Elsevier, 2015. Figure 2: Schematic representation of the over-layer grid system used for analysis on the substrate plane. Note that the dashed line is the “over-layer grid system” and only a guide to the eye for the profilometry measuring points. CdTe layers were deposited on 3 mm thick 20 \(\times\) 30 cm\({}^{2}\) Neoceram\({}^{\text{TM}}\) (Ceramic Glass Ltd., Loughborough, England) type glass rectangles for static mode operation. The area and coverage of the deposited (\(A_{dep}\)) layers were assessed over the central 15 cm \(\times\) 15 cm area using the over-layer grid system shown in Figure 2 (static), by which any spread in the deposited film thickness and the deposited volume (\(v_{exp}\)) of the material was determined. The material utilisation (\(Uv_{mat}\)) was calculated using Equation (1).