# Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment
## 4 Results and Discussion  
### Static Mode - Deposition Profile  
A series of CdTe thin films were grown with \(t_{d}\) = 20 min, \(T_{s}\) = 430 \({}^{\circ}\)C and \(F_{Total}\) = 0.5 L/min. In order to study the deposition profile behaviour, the RFO sizes and active exhaust were varied, as shown in Table 1.  
The deposition profiles shown in Figure 4 highlighted that thin-film growth was strongly dependent on the RFO configuration. The change in the active exhaust from \(-\)10 to \(-\)15 Torr (S-2 to S-3) had very little impact on the material utilisation when compared with S-2. From CFD simulations, the velocity profile was obtained 8 mm upstream and downstream of the injector slit (Figure 5a). The configuration of RFOs in S-1 resulted in a greater flow direction downstream of the injector due to the extraction being stronger with 0.7 mm and 0.5 mm RFOs in situ for RFO-A and RFO-B, respectively. However, by alternating the configuration, as in S-4, reduced the extraction strength downstream, resulting in a recirculating vortex located behind the injector slit and in front of the flow guide plate. The film thickness (\(d\)) data for the extreme cases (S-1 and S-4), presented in Figure 5b, confirmed that the deposited profile was narrower and the peak (maximum) film thickness was greater with S-4. This was expected to be related to the vortex generated near the flow guide plate compared with S-1, as seen in Figure 6a,b. Figure 6 only shows the exhaust located behind the injector RFO-A, the guide flow plate was located in this section and had a direct influence on the overall deposited layer due to the presence of the recirculating vortex in S-4 RFO configuration. The downstream extraction point (RFO-B) had no direct influence or change in the fluid flow pattern and, therefore, only this exhaust is presented in Figure 6. The vortex provided an alternative route to increase residence time on the surface of the substrate for the unreacted precursors to be recycled, therefore, increasing the material utilisation, as shown in Figure 7. However, due to the recirculating vortex, the overall uniformity of the deposited layer was affected with such configuration. Therefore, S-1 configuration was chosen for dynamic mode analysis, depositing a larger uniform surface area.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Configuration**} & \multicolumn{2}{c}{**RFO Size (mm)**} & \multicolumn{2}{c}{**Active Extraction**} \\  & **(RFO-A)** & **(RFO-B)** & **(Torr)** \\ \hline S-1 & 0.5 & 0.7 & \(-\)10 \\ S-2 & 0.7 & 0.5 & \(-\)10 \\ S-3 & 0.7 & 0.5 & \(-\)15 \\ S-4 & 1.0 & 0.5 & \(-\)10 \\ \hline \hline \end{tabular} RFO - Restricted Flow Orifice.  
\end{table}
Table 1: Parametric variables for static mode (locations of RFO-A and RFO-B are shown in Figure 1).  
Figure 4: Cadmium Telluride (CdTe) static deposition profiles from experimental samples (bottom) and computational fluid dynamics (CFD) simulations (top). Deposition conditions varied from S-1 (**a**) to S-4 (**d**) in sequence, as given in Table 1.  
Figure 5: (**a**) Flow velocity profile (m/s) 8 mm in the front and behind the precursor injector slit for S-1–S-4 configurations. (**b**) Mapping of CdTe film thickness profiles obtained in static mode for deposition conditions S-1 and S-4.  
Figure 6: Path lines located behind the precursor injector slit (i.e., near RFO-A in Figure 1) around the flow guide plate and the exhaust (**a**) for S-1 and (**b**) for S-4.