# Amorphous Oxide Thin Film Transistors with Nitrogen-Doped Hetero-Structure Channel Layers
## 3 Results  
Figure 2 shows the O1s XPS spectra of a-IGZO:N and a-IZO:N thin films. The same processing conditions for the film depositions were used as were adopted for the corresponding TFTs. The spectra were calibrated by tacking the C1s (\(\sim\)284.8 eV) reference. Figure 2a,b show the de-convolution of O1s XPS spectra for the a-IGZO:N and a-IZO:N thin films, respectively. Gaussian fitting was used to de-convolve the O1s peaks, which could be fitted by three components, centered approximately at 530 \(\pm\) 0.1 eV (O\({}_{1}\) peak), 531 \(\pm\) 0.3 eV (O\({}_{2}\) peak), and 532 \(\pm\) 0.2 eV (O\({}_{3}\) peak). The O\({}_{1}\) peak is supposed to reflect the oxide lattices in the stoichiometric wurtzite structure without oxygen deficiency; the O\({}_{2}\) peak represents the oxide lattices in the oxygen-deficient region (\(V_{\text{O}}\)). The O\({}_{3}\) peak is usually considered to be related to the chemisorbed hydroxide (e.g., moisture etc.) [26; 27; 28]. To quantitatively study each component of the O1s peak, we defined the Area and %Area to denote the de-convolution area and the de-convolution area percentage of each sub-peak over the O1s peak as follows:  
\[\text{Area(O}_{\text{total}})=\text{Area(O}_{1})+\text{Area(O}_{2})+\text{ Area(O}_{3}), \tag{1}\]  
\[\text{\%Area(O}_{2}/\text{O}_{\text{total}})=\text{Area(O}_{2})/\text{Area( O}_{\text{total}})\times 100\%, \tag{2}\]  
\[\text{\%Area(O}_{3}/\text{O}_{\text{total}})=\text{Area(O}_{3})/\text{Area( O}_{\text{total}})\times 100\%. \tag{3}\]  
Figure 2: The X-ray photoemission spectroscopy (XPS) measurement and analysis results: (**a**) O1s spectra of the a-IGZO:N film; (**b**) O1s spectra of the a-IZO:N film; and (**c**) %Area of each component in O1s detected by XPS. As shown in Figure 2c, the %Area (O\({}_{2}\)/O\({}_{\text{total}}\)) and %Area (O\({}_{3}\)/O\({}_{\text{total}}\)) of a-IGZO:N films were 13.7% and 14.3%, respectively. However, the %Area (O\({}_{2}\)/O\({}_{\text{total}}\)) and %Area (O\({}_{3}\)/O\({}_{\text{total}}\)) of a-IZO:N films were much larger (19.9% and 35.4%), implying that there were more \(V_{\text{O}}\) and trap states in the a-IZO:N films relative to those in the a-IGZO:N films. In addition, the a-IZO:N films tended to adsorb much more moisture gas at the film surface than the a-IGZO:N films. Figure 3 shows the root mean square (RMS) roughness and resistivity of a-IGZO:N and a-IZO:N thin films. The roughness of a-IGZO:N film (0.28 nm) was a little larger than that of a-IZO:N film (0.21 nm). In addition, the a-IZO:N exhibited a much smaller resistivity (2.7 \(\Omega\)cm) than the a-IGZO:N (58 \(\Omega\)cm ). This might be because a-IZO:N contained more \(V_{\text{O}}\) (electrons) than a-IGZO:N. This agreed well with the XPS measurement data (as shown in Figure 2). Figure 4 shows the transfer curves of the AOS TFTs with a-IGZO:N/a-IZO:N (Sample I) and a-IZO:N/a-IGZO:N (Sample II) channel layers, respectively. The corresponding performance parameters were extracted and listed in Table 1. Here, the \(\mu_{\text{FE}}\) was calculated from the maximum slope, that was extracted graphically from the square root of drain current, \(I_{\text{DS}}\)\({}^{1/2}\), versus gate voltage, \(V_{\text{GS}}\), in the saturation region [29; 30]. The \(V_{\text{TH}}\) was achieved from the gate voltage value where \(I_{\text{DS}}\)/(\(W/L\)) = 100 nA. The SS was obtained from the half value of the difference between the gate voltages corresponding to the drain current of 10\({}^{-10}\) A and 10\({}^{-8}\) A, respectively. The on-off current ratio (\(I_{\text{ON}}\)/\(I_{\text{OFF}}\)) was defined as the ratio of the maximum turn-on current to the minimum turn-off current. Conventional AOS TFTs, i.e., the devices with single channel-layers (a-IGZO TFTs, a-IGZO:N TFTs, etc. ), generally have \(\mu_{\text{FE}}\) of less than 10 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)[10; 12; 31].