Paper TF-TuA8
In-situ Conductance Measurements during Transparent Conductive Zinc Oxide Film Growth using Low Temperature Atomic Layer Deposition

Tuesday, October 21, 2008, 4:00 pm, Room 302

Zinc oxide has been extensively studied for applications such as solar cells, flat panel displays, gas sensors etc., and is considered as an alternative to indium tin oxide due to its low-cost, non-toxicity, and chemical and thermal stability. For the flexible device and TFT applications, low growth temperature (<150 ^oC) or low carrier concentration (<10¹⁸ cm^-3) is required. Here we report the low temperature atomic layer deposition (ALD) of zinc oxide using diethyl zinc and water as a precursor and reactant, respectively. We have developed a method to examine conductance in situ during ALD ZnO growth using two metal electrodes (Au/Cr) isolated by a thermally grown SiO₂ with a gap of 1 mm. Conductance was measured in situ during initial nucleation and steady state film growth at temperatures between 100-140 ^oC. The growth rate, electrical resistance, surface morphology, and crystallininty were also studied ex situ as a function of growth temperature and ALD cycles. At 120 ^oC the growth rate of ZnO ALD on SiO₂/Si was ~1.9 Å/cycles with ~3 cycles of incubation time and linear with the number of cycles. At 120 ^oC with 0.1V applied, the current was below the detection limit (<10^-11 A) for the first 42 cycles. The current increased exponentially from 10^-11 to 10^-7 A between 43 and 50 cycles and followed by percolation to 10^-5 A. From 70 to 200 cycles the current increased linearly from 10^-5 to 5x10^-4 A. Interestingly, the effect of each reactant exposure on the conductance of ZnO film during growth was quite different. Specifically at 120 ^oC, both DEZ and water exposure dramatically increased the conductance of ZnO film at the exponential nucleation region. Meanwhile the DEZ exposure decreased and the water exposure increased the conductance of ZnO at the ohmic linear region. This technique shows a potential for in-depth understanding of the ALD ZnO growth process in situ and also how each reactant is involved in the defect formation related to the carrier concentration within the growing ZnO film.