# Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment
## 4 Results and Discussion
### Dynamic Mode - Deposition Kinetics
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Total Flow** & **T** & **Exp (_d_)** & **CFD (_d_)** & **Exp (_U__T__T__T__T_)** & **CFD (_U__T__T__T_)** \\
**(I/min)** & **(\({}^{\circ}\)C)** & **(\(\mu\)m)** & **(\(\mu\)m)** & **Avd** & **Stdv** & **Avd** & **Stdv** & **(\%)** \\ \hline \multirow{9}{*}{0.5} & 225 & - & 0.018 & - & - & - & - & 1.47 \\  & 265 & - & 0.066 & - & - & - & - & 5.42 \\  & 305 & 0.172 & 0.178 & 18.56 & 0.30 & 14.20 & 0.47 & 14.71 \\  & 350 & 0.339 & 0.359 & 28.12 & 0.29 & 27.94 & 0.88 & 29.60 \\  & 390 & 0.450 & 0.533 & 38.11 & 0.31 & 37.10 & 1.81 & 43.98 \\  & 430 & 0.598 & 0.621 & 50.90 & 0.31 & 49.32 & 0.39 & 51.17 \\  & 470 & 0.634 & 0.626 & 39.29 & 0.35 & 52.29 & 0.21 & 51.67 \\  & 515 & - & 0.604 & - & - & - & - & 49.88 \\  & 555 & - & 0.538 & - & - & - & - & 44.43 \\ \hline \multirow{9}{*}{1.0} & 225 & - & 0.009 & - & - & - & - & 0.36 \\  & 265 & - & 0.046 & - & - & - & - & 1.92 \\  & 305 & 0.175 & 0.180 & 7.34 & 0.30 & 7.22 & 0.51 & 7.42 \\  & 350 & 0.474 & 0.493 & 18.20 & 0.29 & 19.56 & 1.58 & 20.36 \\  & 390 & 0.799 & 0.926 & 29.30 & 0.32 & 33.56 & 2.48 & 38.24 \\  & 430 & 1.257 & 1.213 & 45.80 & 0.30 & 51.91 & 7.20 & 50.10 \\  & 470 & 1.209 & 1.248 & 45.70 & 0.38 & 49.94 & 0.47 & 51.56 \\  & 515 & - & 1.130 & - & - & - & - & 46.66 \\  & 555 & - & 1/133 & - & - & - & - & 46.66 \\  & 555 & - & 1/133 & - & - & - & - & 46.80 \\ \hline \end{tabular} Total Flow – precursor total flow; T – substrate temperature. Exp (_d_) – experimental layer thickness; CFD (_d_) – numerical layer thickness; Exp (_U__T__T_), Exp (_U__T__T_) – experimental results for material utilization; Avd – averaged results; Stdv – standard deviation; CFD (_U__T__T_) – numerical results for material utilization.  
\end{table} 
Table 2: Layer thickness and material utilization as a function of \(T_{s}\) from 305 \({}^{\circ}\)C to 470 \({}^{\circ}\)C for \(F_{total}=\) 0.5 L/min and \(F_{total}=\) 1.0 L/min. Figure 9: Material characterisation of deposited CdTe using the S-1 configuration for the chamberless coating head; results are displayed as (**a**) EDX result, presenting an elemental composition of the measured sample, and (**b**) SEM results, showing the surface topology and grain structure of CdTe deposited layer. transport limited regime; further study of the fluid dynamics would provide potential to reach higher usage of the precursors. The gravimetric measurements from Table 2 provided the most reliable values, considering that they were less influenced by non-uniformity in thickness. The variations between experimental and simulated data could be attributed to the fact that CFD modelling uses a simplified environment and chemical reaction (Equation (6)). Further increase of \(T_{s}\) above 500 \({}^{\circ}\)C reduced material utilisation, which could be attributed to desorption of tellurium species from the growth surface, as calculated from CFD modelling (Table 2) and previously observed by [PERSON] et al. (2011). Material utilisation of 50%-60% could be reproducibly achieved when the pyrolysis of CdTe takes place at temperatures between 430 \({}^{\circ}\)C and 470 \({}^{\circ}\)C, as could be seen from Table 2. It is expected that the residence time of precursors on the substrate surface could be further improved, leading to higher material utilisation; this would be the subject of further investigation. At higher gas flow, the precursor material utilisation is maintained whilst doubling the film thickness. Overall, the presented results indicated that the use of smaller total flows (at fixed precursor concentrations) was more beneficial in regards to high efficiency in material consumption (Figure 10).