Composition, Microstructure, and Electrical Performance of Sputtered SnO Thin Films for p-Type Oxide Semiconductor

Abstract

p-Type SnO thin films were deposited on a Si substrate by a cosputtering process using ceramic SnO and metal Sn targets at room temperature without adding oxygen. By varying the dc sputtering power applied to the Sn target while maintaining a constant radio frequency power to the SnO target, the Sn/O ratio varied from 56:44 to 74:26 at the as-deposited state. After thermal annealing at 180 °C for 25 min under air atmosphere using a microwave annealing system, the films were crystallized into tetragonal SnO when the Sn/O ratio increased from 44:56 to 57:43. Notably, the metallic Sn remained when the Sn/O ratio was higher than 55:45 at an annealed state. When the ratio was lower than 55:45 at the annealed state, the incorporated Sn fully oxidized to SnO, making the films useful p-type semiconductors, whereas the films became metallic conductors at higher Sn/O ratios. At the Sn/O ratio of 55:45 at the annealed state, the film showed the highest Hall mobility of 8.8 cm V s and a hole concentration of 5.4 × 10 cm. Interestingly, the electrical conduction behavior showed trap-mediated hopping when the Sn metal was cosputtered, whereas the single SnO film showed regular band conduction behavior. The residual stress effect could interpret such property variation originated from the sputtering power and postoxidation-induced volumetric effects. This report makes a critical contribution to the in-depth understanding of the composition-structure-property relationship of this technically important thin film material.

P‐11: Carrier Concentration Reduction by Fluorine Doping in P‐Type SnO Thin‐Film Transistors

“…A high hole concentration (nh) of × cm -3 is obtained in the untreated SnO film, with a resistivity (ρ) of 0.5 Ω·cm and a Hall mobility (μHall) of 1 cm 2 /Vs. These are comparable to those reported in the literature [8][9]. When the fluorination treatment time increased from 0 s to 60 s, nh significantly decreased to .…”

SnOx thin films with tunable conductivity for fabrication of p–n homo‐junction

“…Thin films deposited at ppO 2 values between 9.5% and 15.3% presented high resistivity (~1 × 10 5 Ω·cm), and Hall measurements could not be obtained. Similar behavior has also been reported previously 10,11 . On the other hand, at ppO 2 greater than 15.3%, the thin films exhibited n‐type conductivity behavior, which could be caused by the formation of SnO 2 crystalline phases 13 .…”

“…Similar behavior has also been reported previously. 10,11 On the other hand, at ppO 2 greater than 15.3%, the thin films exhibited n-type conductivity behavior, which could be caused by the formation of SnO 2 crystalline phases. 13 A remarkable finding was that by increasing the ppO 2 from 4.8% to 18.5%, the carrier type of the SnO x thin films was tuned from p-type to n-type.…”

“…9 Among the p-type oxides, tin oxide (SnO) has recently received increased attention due to the ease of changing its carrier type from p to n by varying the relative oxygen partial pressure during the deposition process. [10][11][12] The p-type behavior of SnO thin films occurs when the O 2p and Sn 5s orbitals are hybridized. This hybridization increases the metallic-ions contributions improving the p-type mobility.…”

“…More recently, Lee and coworkers studied the mobility in p‐type SnO x thin films doped with Sn, deposited by reactive magnetron sputtering. They reported that increasing the amount of Sn during the deposition leads to a linear increase in mobility and carrier concentration, until a threshold of Sn content is overcome and from that point forward the mobility begins to decrease 11 . Nonetheless, it should be noted that a different approach to growing both p‐ and n‐type SnO x thin films is using a SnO/Sn composite target 15 or a SnO target 16 by radio‐frequency (RF) sputtering.…”