Phosphorus speckled ZnMgO emits ultraviolet(UV) light bright enough for making UV lasers and LEDs.

Ultraviolet(UV) light is widely used in medicinal and biological applications, semiconductor processing, optical communication etc. Owing to its vast applications, scientists are studying various materials and designs to make efficient and cheap sources of UV light. In their efforts towards this, Prof. S. Chakraborti and his team at IITBNF have tweaked an oxide material to make it more suitable for UV lasers & light emitting diodes(LEDs).

Typically, lasers made using direct bandgap semiconductors need a large number of electron-hole pairs – i.e. excitons - to be created. Excitons are formed when electrons from valence band are raised to conduction band, leaving behind a hole in valence band. It turns out that the raised electrons cannot stay in the conduction band for a long time and fall back into the valence band by losing their energy in the form of light. Whether the light is UV or not depends on the band gap of the semiconductor.

ZnMgO is a direct band gap semiconductor with a bandgap that can give UV light. In order to increase UV light emission in ZnMgO, Prof. Chakrabotrti’s team introduced phosphorus(P) atoms into this material. Through photoluminescence measurements, they found that doping with phosphorus atom increases exciton formation in ZnMgO. The team speculates that the P atom introduces an energy level inside the bandgap of ZnMgO, close to the conduction band edge. This enhances exciton formation. Thus, more UV light can be emitted. This tweak can enable design of more efficient lasers & LEDs, operating in UV region.

- Pankaj Kumbhare

Work funded/ supported by: Department of Science & Technology & Department of Electronics & Information Technology (DietY), Government of India.

Published paper: Shantanu Saha, Saurabh Nagar, Subhananda Chakrabarti, "Effects of Phosphorus Doping by Plasma Immersion Ion Implantation on the Structural and Optical Characteristics of Zn0.85Mg0.15O", Applied Physics Letters, Vol. 105, No.6, pp.061109, (2014).