Generation of plasma emission from porous silicon

Plasmas was generated inside pores of porous silicon and the plasma can act as a light source, thus, forming a solid state plasma emission device. Porous silicon layer was etched from n⁺ silicon using electrochemical method. A top layer of metal alloy was deposited as top contact, and the bottom contact is Al. By biasing the top contact positive, it was successful to generate the plasma at a voltage as low as 19 V DC. The cause of ionization of the gas is attributed to electron emission from sharp tips within the pores under the introduction of high field created inside the pores. In reduced air/nitrogen pressure, strong nitrogen plasma lines were observed. The strongest peak of the UV electroluminescence (EL) occurs at 337 nm. Although red electroluminescence from porous silicon itself can be observed, it is order of magnitude smaller than that of N₂ plasma emission. By replacing the air/nitrogen with argon, Ar plasma emission can be obtained (main peak at 750.5 nm). This shows that colour tunability is possible by introducing different gases into porous silicon. Although power output from the emission is estimated to be of the order of μW, there is a lot room for improvement such as replace the metal contact by transparent conducting oxide like ITO and also adopt pulse operation would potentially generate higher power output. The results show that the device has the potential in plasma display and bio-agent detection applications.