Structural, optical and electrical properties of Ti doped amorphous silicon prepared by co-sputtering

• Introducing Ti enhances the absorption of a-Si in visible and infrared region.
• Co-sputtering with high Ti content results in n-type a-Si.
• XPS demonstrates titanium silicide exists without metallic Ti precipitating.
• Low content Ti atoms partly compensate dangling bonds of amorphous Si network.
• Heavily doping Ti atoms mainly compensate the unpaired electrons in the band tail.

Titanium-doped unhydrogenated amorphous silicon (a-Si: Ti) films were prepared by rf co-sputtering. Structural, optical and electrical properties of a-Si: Ti as a function of Ti content were investigated by RBS(Rutherford Backscattering Spectrometry), XPS(X-ray Photoelectron Spectroscopy), Raman, ESR (Electron Spin Resonance), Spectroscopic Ellipsometry, thermoelectric tests and temperature dependent I–V tests. Introducing Ti impurity in amorphous Si results in n-type material, room temperature conductivity increases more than three orders of magnitude and activation energy decreases obviously. When Ti content is lower than 2 at.%, the degree of short-range order and defect state density of amorphous Si network improve while the optical bandgap changes little. However, with Ti content higher than 2 at.%, the degree of short-range order decreases and the optical gap of a-Si shrinks. The role of Ti atoms in amorphous Si network is discussed. ESR results confirm that introducing low content of Ti can compensate the dangling bonds of amorphous Si, while with Ti content higher than 2%, most Ti atoms compensate the unpaired electrons in the conduction band tail.