Effect of Ge incorporation on the performance of p-channel polycrystalline Si_{l - x}Ge_x thin-film transistors

In this study, p-channel polycrystalline silicon-germanium thin-film transistors (poly-Si_{l - x}Ge_x TFTs) with different Ge contents in the channel layer were fabricated and characterized. A novel device process was developed to fabricate the test samples. The device structure utilized the in situ boron-doped poly-Si_0.79Ge_0.21 with an extremely low resistivity (below 2 mΩ cm) as the source/drain and the undoped poly-Si (or Si_{l - x}Ge_x) as the channel layer. It is observed that the addition of Ge atoms in the channel would significantly increase the amount of trap density at grain boundaries thus degrading the device performance. Based on these results, we recommend the use of poly-Si_{l - x}Ge_x source/drain to reduce the contact resistance but do not recommend that it is appropriate to replace poly-Si as the channel material of TFTs.