Controlling Carrier Type and Concentration in NiO Films To Enable in Situ PN Homojunctions

Area of Science:

• Materials Science
• Semiconductor Physics
• Thin Film Deposition

Background:

• Nickel oxide (NiO) is a p-type semiconductor with applications in electronics.
• Controlling carrier type and concentration is crucial for advanced semiconductor devices.
• Low-temperature deposition processes are desirable for utilizing flexible substrates like glass.

Purpose of the Study:

• To investigate the effect of oxygen partial pressure on NiO properties during reactive sputtering.
• To achieve controllable n-type and p-type NiO films.
• To demonstrate a NiO homojunction fabricated using a simple, low-temperature process.

Main Methods:

• Reactive sputtering of a Ni target in an oxygen atmosphere.
• In situ deposition of NiO layers at 200 °C.
• Carrier type and concentration control via oxygen partial pressure.
• Transmission Electron Microscopy (TEM) for interface analysis and stoichiometry (Ni:O ratio).

Main Results:

• Achieved both n- and p-type NiO films with carrier concentrations tunable from 10^19 to 10^14 cm^-3.
• Successfully fabricated a NiO homojunction by layering n-type and p+-type NiO.
• Demonstrated low-temperature deposition (200 °C) on glass substrates.
• Experimental band diagrams for n-type NiO were obtained for the first time.
• TEM analysis confirmed high-quality interfaces and the impact of oxygen on stoichiometry.

Conclusions:

• Oxygen partial pressure is a key parameter for controlling NiO stoichiometry, carrier type, and concentration.
• The developed sputtering process allows for simple, low-temperature fabrication of tunable NiO films and homojunctions.
• This work opens possibilities for NiO-based devices on flexible substrates.