# Amorphous Oxide Thin Film Transistors with Nitrogen-Doped Hetero-Structure Channel Layers
## 3 Results
The N-doped DSCL TFTs (Samples I and II), however, exhibited apparent improvements in their field-effect mobilities, as shown in Table 1. If we compare these two samples, Sample II showed even better electrical performance on the whole than Sample I, although its field-effect mobility (15.0 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)) was smaller than that of Sample I (31.9 cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\)). To be specific, Sample II exhibited a more positive \(V_{\text{TH}}\) (1.5 V) and a smaller SS value (0.5 V/dec) than Sample I. As shown in Table 1, \(I_{\text{ON}}\)/\(I_{\text{OFF}}\) values of both the samples were larger than 10\({}^{8}\). \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & \(\mu_{\text{FE}}\) **(cm\({}^{2}\cdot\)V\({}^{-1}\cdot\)s\({}^{-1}\))** & **SS (V/dec)** & \(V_{\text{TH}}\) **(V)** & \(I_{\text{ON}}\)**/\(I_{\text{OFF}}\)** \\ \hline I & 31.9 & 0.8 & \(-\)5.0 & \(1.2\times 10^{8}\) \\ \hline II & 15 & 0.5 & 1.5 & \(1.1\times 10^{8}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Extracted performance parameters of the N-doped DSCL TFTs. Figure 3: Root mean square (RMS) roughness and resistivity of a-IGZO:N and a-IZO:N thin films. Figure 5 shows the transfer curves evolution of the N-doped DSCL TFTs under positive bias stress (PBS) and negative bias stress (NBS) tests for 2500 s, respectively. Here, the gate electrodes were stressed at +30 V for PBS and \(-\)30 V for NBS for a period and then the transfer curves were instantly measured. As shown in Figure 5a,b, Sample I showed more stable PBS properties with a smaller \(V_{\text{TH}}\) shift of +0.5 V, whereas Sample II exhibited a little larger \(V_{\text{TH}}\) shift (+1.5 V) for the PBS duration. However, during NBS testing (Figure 5c,d), the \(V_{\text{TH}}\) shift of Sample I became much worse (\(-\)9.0 V) than that of Sample II (\(-\)0.5 V). In short, Sample I showed better PBS stability (\(V_{\text{TH}}\) shift of +0.5 V) and Sample II exhibited much more stableelectrical properties (\(V_{\text{TH}}\) shift of \(-\)0.5 V) for NBS tests. Figure 4: Transfer curves of the N-doped DSCL TFTs (Samples I (a-IGZO:N/a-IZO:N TFT) and II (a-IZO:N/a-IGZO:N TFT)). Figure 5: Bias stress stability of the N-doped DSCL TFTs: (**a**) positive bias stress (PBS) of the a-IGZO:N/a-IZO:N TFT (Sample I); (**b**) PBS of the a-IZO:N/a-IGZO:N TFT (Sample II); (**c**) negative bias stress (NBS) of the a-IGZO:N/a-IZO:N TFT (Sample I); and (**d**) NBS of the a-IZO:N/a-IGZO:N TFT (Sample II). The stressing conditions were \(V_{\text{GS}}\) = +30 for PBS and \(V_{\text{GS}}\) = \(-\)30 for NBS. The transfer curves were obtained with \(V_{\text{DS}}\) = 10 V.  
Figure 6 shows the transfer curve evolution of the N-doped DSCL TFTs under thermal stress. From here, one might notice that these two samples exhibited markedly different negative \(V_{\rm TH}\) shifts. As shown in Figure 6, the \(V_{\rm TH}\) of Sample I shifted up to \(-11.5\) V as the temperature increased from 298 to 398 K, indicating that Sample I had muchrowsethermal stability. In comparison, Sample II was more stable under thermal stress, with a \(V_{\rm TH}\) that only shifted \(-2.5\) V.  
Here we summarize the interesting results related to the N-doped DSCL TFTs. The \(\mu_{\rm FE}\) of AOS TFTs could be largely improved by using the DSCL composed of a high-defect-density channel layer and a low-defect-density channel layer to form the hetero-junction structure [19; 21].