# Thin CdTe Layers Deposited by a Chamberless Inline Process using MOCVD, Simulation and Experiment
## 4 Results and Discussion
### Dynamic Mode - Deposition Kinetics  
A series of CdTe thin films were grown using the S-1 configuration, with \(F_{Total}\) = 1.0 L/min and \(v_{sub}\) = 1.8 cm/min, where only \(T_{s}\) was varied in order to correlate the kinetic regime of the pyrolysis of CdTe layer with CFD simulations (Figure 8a). The activation energy (\(E_{a}\)) of the surface kinetic reaction was calculated from Equation (8) using the linear range from the Arrhenius plot in Figure 8a. \[\ln(GR)=\ln(A)-\frac{E_{a}}{RT_{s}} \tag{8}\]  
where \(GR\) is the growth rate, and \(R\) is the gas constant (8.314 J/K-mol). Saturation of \(GR\) was observed for \(T_{s}\) > 420 \({}^{\circ}\)C; therefore, the linear region in the lower temperature range was used to calculate \(E_{a}\), with a value of 59.62 kJ/mol. This appeared to be somewhat larger than the results experimentally obtained by [PERSON] et al. [12] (49 kJ/mol) for a slightly larger VI:II precursor ratio for deposition in an enclosed inline MOCVD reactor (Figure 8b). [PERSON] et al. [12] also observed saturation in \(GR\) at higher temperatures (i.e., >405 \({}^{\circ}\)C), attributed to mass transport limitation due to the Te precursor's concentration. Despite the slightly higher activation energy, the activation energy as a function of VI:II ratio followed the trend observed by previous authors [12; 21] within experimental errors. Using the S-1 configuration, a series of CdTe thin films were grown for \(F_{Total}\) = 0.5 L/min and \(F_{Total}\) = 1.0 L/min while maintaining the precursor partial pressures constant at DMCd = 3.48 Torr and DIPTe = 1.08 Torr, \(v_{sub}\) = 1.8 cm/min, while varying \(T_{s}\) (Table 2). Figure 8: Using the S-1 configuration for the chamberless coating head during the deposition of CdTe, results are displayed as (**a**) an Arrhenius plot of \(\ln(GR)\) vs 1/\(T\) used to calculate the activation energy and (**b**) a VI:II precursor ratio vs activation energy. GR: growth rate. Figure 7: Material utilisation calculated using (1) for S-1–S-4 configurations. The deposited layers were further examined for CdTe characterisation. The elemental analysis of the CdTe layers was conducted using energy dispersive X-Ray (EDX) spectroscopy analytical technique; Figure 9a presents the elemental composition of the measured specimen. Furthermore, scanning electron microscopy (SEM) presented in Figure 9b shows the surface topography and grain structure of the deposited layer. The utilisation of CdTe layer grown using the chamberless inline deposition system has been achieved by [PERSON] et al. [13] in a photovoltaic solar cell device and obtaining device results comparable with horizontal (tube) MOCVD batch reactor. From Table 2, it is clear that both the film thickness and material utilisation were increased with \(T_{s}\) up to \(\sim\) 470 \({}^{\circ}\)C; however, a plateau was reached for higher temperatures. In relatively low \(T_{s}\) regime, ranging from 305 \({}^{\circ}\)C to 420 \({}^{\circ}\)C, the deposition of CdTe was strongly dominated by a second-order kinetic regime. Above 420 \({}^{\circ}\)C, the material utilisation reached a plateau at 50-60%, related to a mass