Effects of Nd in NdxIn1-xO3 Semiconductors for Thin-Film Transistors

Thin-film transistors (TFTs) with neodymium-substituted indium oxide [Nd
_x
In
_1-x
O
₃
(NIO)] semiconductor were fabricated. It was found that NIO films with higher annealing temperature have higher film quality and higher mobility; and NIO films with higher Nd concentration have higher coordination number of In, indicating fewer oxygen vacancies and lower free carrier density. TFTs with different Nd concentration exhibited good electrical stability under positive gate-bias stress, but the ones with lower Nd concentration (5%) displayed much poorer stability under negative gate-bias stress (NBS) compared with those with higher Nd concentration (15% and 25%). Detailed studies showed that the charge transfer satellite with the electron configuration of INd3d
_5/2
⁵
4f
⁴
O2p
^-1
), which originates from the O2p → Nd4 f charge transfer process, was the main reason for poor NBS stability for TFTs with 5% Nd, because it favored a 4f
ⁿ⁺¹
/4f
ⁿ
couple formation, resulting in the formation of donor/acceptor states, which will affect the electrical stability.