Causes of the Difference Between Hall Mobility and Field-Effect Mobility for p-Type RF Sputtered Cu₂O Thin-Film Transistors
Jaesung Jo, Julia D. Lenef, Kishwar Mashooq, Orlando Trejo, Neil P. Dasgupta, Rebecca L. Peterson
Abstract
The high Hall hole mobility (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hall</sub> ) of cuprous oxide (Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O) has caused great interest in using this semiconductor for p-type devices in a future complementary metal-oxide-semiconductor (CMOS) thin-film transistor (TFT) technology. However, in most studies, the field-effect mobility (μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> ) achieved was reported to be much lower than μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hall</sub> . To understand the large gap between μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hall</sub> and μFE, in this work, we correlate RF sputtered p-type copper oxide (CuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) material properties with electrical characteristics by varying the film thickness. After vacuum annealing, the different thicknesses cause differences in the oxidation state and phase. Our results show that films with a higher Cu(I) fraction that form in the Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O phase give better TFT performance than CuO films. Nonetheless, the TFTs still exhibit a much lower μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> of 0.005-0.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s than the measured μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Hall</sub> value of 12.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V-s. We explore the reasons for this mobility gap by conducting contact resistance (RC) and interface trap (D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub> ) analysis. We find that the mobility difference can be minimized by reducing the high contact resistance (~33% of the total resistance in the ON-state) and high density of interface traps (~3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">13</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> eV <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ).