Thickness dependent structural, optical and electrical properties of Ti-doped ZnO films prepared by atomic layer deposition

ALD of ZnO:Ti: Growth Mechanism and Application as an Efficient Transparent Conductive Oxide in Silicon Nanowire Solar Cells

“…The crystallites have an apparent rice grain shape (average grain size ~ 80 nm), which is different from the round shaped grains of undoped ZnO (Figure 2), as described elsewhere. 27 The sequence B leads to thicker films with higher [Ti]/[Zn] atomic ratio (as determined from EDS measurements), which is consistent with its higher mass gain observed previously by QCM analysis. In fact, in case of sequence B, the TTIP precursor is pulsed on an OH-terminated surface, which is more reactive than a Zn-Et terminated one, and leads to a higher mass gain over the TiO2 cycle (Figure 1d).…”

“…All films are n-doped and the carrier concentration slightly increases with the film thickness (N = 10 20 -10 21 cm -3 ), as well as the mobility (1 -150 cm 2 V -1 s -1 ), which is in accordance to previously reported systems. 23,[25][26][27]29 It seems that thinner films (thickness < 50 nm) suffer significantly from the grain boundaries scattering due to the presence of smaller grains. 27 The resistivity of all films is in the order of 10 -3 Ω cm; the lowest resistivity value of 5 × 10 -4 Ω cm is seen for 150 nm thick films, which is slightly more conductive than systems reported by Bergum et al 27 Interestingly, the FoM increases monotonically as a function of the film thickness for TZO (Figure 4b).…”

“…23 Moreover, titanium-doped zinc oxide (TZO) has a higher work function than AZO which for example makes it more suitable as anode for OLED applications. 24 Compared to AZO, TZO by ALD has been explored to a much smaller extent, 23,[25][26][27][28][29] and so is the Ti-Zn-O system. [30][31][32][33] Most processes for TZO use DEZ, H2O and titanium (IV) i-propoxide (TTIP) as precursors, with a supercycle strategy.…”

“…[30][31][32][33] Most processes for TZO use DEZ, H2O and titanium (IV) i-propoxide (TTIP) as precursors, with a supercycle strategy. 23,[25][26][27]29 The influence of the cycle ratio on the material properties has been previously investigated for different film thicknesses and the optimum range of cycle ratio is reported {TiO2}:{ZnO} ~ 1:10 -1:20. [25][26][27]29 Resistivity values as low as 8.9 × 10 -4 Ω cm with high transparencies (>80%) have been obtained for 100 nm-thick films.…”

“…Both films are equally transparent with transmittance values above 80% in the 400-1300 nm region (Figure 3b), which is in agreement with previously reported ALD-TZO films. 23,[25][26][27][28] Finally, as the target properties for a TCO are high transmission and conductivity values, the sequence A was selected for the rest of the study.…”