Evidence for the bias-driven migration of oxygen vacancies in amorphous non-stoichiometric gallium oxide

Abstract

The conductivity of gallium oxide thin films is strongly dependent on the growth temperature when they deposited by pulsed laser deposition under vacuum environment, exhibiting an insulative-to-metallic transition with the decrease of the temperature. The high conductive gallium oxide films deposited at low temperature are amorphous, non-stoichiometric, and rich in oxygen vacancy. Large changes in electrical resistance are observed in these non-stoichiometric thin films. The wide variety of hysteretic shapes in the I-V curves depend on the voltage-sweep rate, evidencing that the time-dependent redistribution of oxygen vacancy driven by bias is the controlling parameter for the resistance of gallium oxide.

Recent Progress of Deep Ultraviolet Photodetectors using Amorphous Gallium Oxide Thin Films

“…[ 35 ] Wu et al fabricated a series of gallium oxide thin films on sapphire substrate via PLD with T s ranging from 250 to 650 °C and found that the crystallization procedure started at about 450 °C as well as a blue shift presenting at the absorption edge (from 4.6 to 5.1 eV) with T s increasing from 450 to 650 °C. [ 37 ] In the study by Guo et al, [ 74 ] gallium oxide films were deposited on α‐Al 2 O 3 substrates at various T s (500, 550, 600, 650, and 700 °C) in a vacuum environment. At low growth temperature (500 °C), the film is XRD amorphous, strong oxygen deficiency, low transparency, and high conductivity.…”

“…I – V hysteretic loop and current‐turning voltage of the amorphous sample is strongly dependent on the voltage‐sweep rate, which can be attributed to the migration of V O defects driven by bias. [ 74 ] Heinemann et al investigated oxygen deficiency and Sn doping in a‐GaO x thin films grown at a temperature gradient from 425 to 300 °C and from 160 to 100 °C with fixed oxygen partial pressure of 2 × 10 −5 and 1.3 × 10 −3 mbar, respectively. [ 75 ] All the films show an amorphous structure for T s up to 425 °C.…”

Transition between bipolar and abnormal bipolar resistive switching in amorphous oxides with a mobility edge

“…Several experimental investigations have shown that gallium oxide and especially amorphous, substoichiometric gallium oxide thin films (a-GaO , ) exhibit resistive switching 4 – 11 . In contrast to other known resistive switching oxides, such as titania 12 , 13 or strontium titanate 14 , 15 , a-GaO does not need a forming process 4 , 6 , 8 , 9 . According to both experimental and simulation results, the resistive switching can be based on a change in bulk resistance due to the migration of oxygen ions between the blocking electrodes of the device 4 , 6 , 8 , 9 .…”

“…In contrast to other known resistive switching oxides, such as titania 12 , 13 or strontium titanate 14 , 15 , a-GaO does not need a forming process 4 , 6 , 8 , 9 . According to both experimental and simulation results, the resistive switching can be based on a change in bulk resistance due to the migration of oxygen ions between the blocking electrodes of the device 4 , 6 , 8 , 9 . Therefore, the resistance scales with the size of the memristive device, which is an advantage for the downsizing of devices in later applications.…”

“…The curves can either cross at the point of origin, which is called bipolar switching, or they can touch, which is called abnormal bipolar switching or sometimes complementary resistive switching 16 . Both forms have been found experimentally in gallium oxide, but without a connection between them 4 , 6 , 8 , 9 . Table S1 in the supplementary information summarises these experimental results and shows that there is neither agreement on which mechanism is responsible for switching in gallium oxide nor which switching behaviour is observed at all.…”