Post-annealing Temperature Effect on Electrical Properties of Al2O3 Films on Silicon by Atomic Layer Deposition for Solar Cell Applications

2018-11-25
Silicon wafers, being the most dominant and almost inevitable material for solar cell production, require surface passivation to increase the solar cell efficiency by decreasing recombination losses. For this reason, several research groups are currently focused on the usage of thin alumina (Al2O3) as a passivation layer. The success of Tunnel Oxide Passivating CONtact (TOPCon) solar cell, Passivated Emitter Rear Totally diffused (PERT) solar cell and Passivated Emitter Rear solar cell (PERC) structures demonstrate enhanced passivation quality of crystalline silicon (c-Si) solar cells with Al2O3films [1]. The determining parameters for the passivation quality of Al2O3can be summarized as interface trap states (Dit), fixed charge density (Qf) and flat band voltage (VFB). Due to enhanced field effect passivation quality of thin Al2O3layer, high ratio Qfcan be accomplished. Qfhas been reported as high as 1 - 4x1012cm-2in literature by several research groups and this charge density is sensitive to both deposition conditions and post-thermal treatments [2]. In addition to field effect passivation, Al2O3layer also provides chemical passivation with relatively low density of Dit[5]. In this context, the effect of different deposition conditions and post-annealing temperatures on Al2O3films formed by atomic layer deposition (ALD) were investigated using conductance method to identify and clarify relation between interface properties and fixed charge densities under initial deposition conditions varying in between160 - 200°C in combined with various post-annealing conditions (400°C to 600°C for 30 minutes). C-V and G-V measurements were done for each sample with various frequencies from 1kHz to 5MHz. From C-V measurements, the oxide capacitance and VFBvalues were calculated and conductance method was applied to determine Ditvalues. It was shown that Qfdecreased when the post-thermal annealing was applied. The highest Qfwas -5.13x1013cm-2and the lowest one was -2.43x1011cm-2. Ditdecreased at 400°C post-annealing temperature for different deposition temperatures. The highest Ditvalue was 2.79x1013cm-2eV-1and the lowest one was 2.39x1011cm-2eV-1. The lowest Ditwas found at 400°C post-thermal annealing temperature under N2ambient with 165°C prior deposition temperature. It was concluded that when Qfvalues increase, Ditvalues also increase. High variation on VFBwas found where it changed in between 1.09V to 4.19V.
Citation Formats
E. Dönerçark, M. B. İmer, and R. Turan, “Post-annealing Temperature Effect on Electrical Properties of Al2O3 Films on Silicon by Atomic Layer Deposition for Solar Cell Applications,” presented at the MRS Fall Meeting & Exhibit 2018, (25 November 2018 - 30 November 2019), Massachusetts, United States Of America, 2018, Accessed: 00, 2021. [Online]. Available: https://mrsfall2018.zerista.com/event/member/530764.