Herein, we investigate the process–structure–properties relationships of in situ phosphorus (P)‐doped polycrystalline silicon (poly‐Si) films by atmospheric pressure chemical vapor deposition (APCVD) for fabricating poly‐Si passivating, electron selective contacts. This high‐throughput in‐line APCVD technique enables to achieve a low‐cost, simple manufacturing process for crystalline silicon (c‐Si) solar cells featuring poly‐Si passivating contact by excluding the need for vacuum/plasma environment, and additional post‐deposition doping steps. A thin layer of this P‐doped poly‐Si is deposited on an ultrathin (1.5 nm) silicon oxide (SiO
x
) coated c‐Si substrate to fabricate the passivating contact. This is followed by various post‐deposition treatments, including a high‐temperature annealing step and hydrogenation process. The poly‐Si films are characterized to achieve a better understanding of the impacts of deposition process conditions and post‐deposition treatments on the microstructure, electrical conductivity, passivation quality, and carrier selectivity of the contacts which assists to identify the optimal process conditions. In this work, the optimized annealing process with post‐hydrogenation yields passivating contact with a saturation current density (J
0) of 3 fA cm−2 and an implied open‐circuit voltage (iV
OC) of 712 mV on planar c‐Si wafer. Junction resistivity values ranging from 50 to 260 mΩ cm2 are realized for the poly‐Si contacts processed in the optimal annealing condition.
The semiconductor-to-metal transition of vanadium dioxide (VO2) films is studied using temperature-dependent Raman, optical, and electrical measurements. The VO2 films are deposited via an atomic layer deposition (ALD) process using alternate pulses of vanadium tetrachloride and H2O at 350 °C. A growth rate of 0.021 nm/cycle and a thickness of 33 nm of VO2 are obtained for all films studied. The phase of the film is determined using x-ray diffraction. The as-deposited films are amorphous and are transformed to the monoclinic phase with a post-deposition, forming gas anneal at temperatures ≥ 500 °C for 60 min. The purity of the films is determined using x-ray photoelectron spectroscopy and no evidence of residual chlorine is detected. The temperature-dependent Raman Ag mode of the monoclinic VO2 phase is observed to monotonically decrease from 25 °C to 78 °C; where no evidence of the Ag peak is observed in the film beyond 68 °C. The refractive index and extinction coefficient extracted from temperature-dependent ellipsometry confirm that, beyond 68 °C, free carriers are generated in the film. Electrical measurements performed on a fabricated p++Si/VO2/Ti/Au device show a semiconductor-to-metal transition behavior with a high resistance of 14701 ± 2284 Ω at 62 °C and a low resistance of 1064.1 ± 143 Ω at 67 °C. This work demonstrates that a halide-based ALD process provides a clean and robust approach to synthesizing high-quality VO2 films.
Atomic layer deposition is used to synthesize 33 nm thick VO2 films using a vanadiumtetrachloride and H2O. The as-deposited VO2 films are amorphous and convert to the monoclinicphase after a post-deposition anneal ≥ 500 °C, 60-minute in forming gas. X-ray photoelectronspectroscopy suggests the annealed film is stoichiometrically VO2. Temperature-dependentRaman spectroscopy and ellipsometric studies reveal the semiconducting to metallic transition ofannealed and crystallized VO2 thin film. The phase transition temperature is recorded at 68 °C.Refractive index and extinction coefficient from ellipsometry confirm that beyond 68 °C, freecarriers are generated in the film. Electrical measurements performed on a fabricatedp++Si/VO2/Ti/Au device show semiconducting to metallic transition behavior at 68 °C with a high(semiconducting): low (metallic) resistance ratio of 66. A halide based atomic layer depositionchemistry provides a clean and robust approach to synthesizing high-quality VO2 films.
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