Nitride based thin-film research

Joe Trodahl, Ben Ruck, Felix Budde, Annette Koo, Simon Granville.

Nitride based materials have attracted significant attention in recent years due to the great variety of possible physical structures and electronic properties that they display. One particularly interesting example is gallium nitride, which has become the material of choice for use in modern blue-UV optoelectronic devices, such as the diode lasers in the next generation DVD players. At VUW we have developed a strong program growing a range of nitride materials in thin film form, and investigating their optical and electrical properties.

The specific projects include:

Disordered GaN

It has been predicted that the electronic structure of amorphous GaN might make it a cheap substitute for the commercially exploited crystalline form. We have successfully grown nanocrystalline GaN films, but we have found that to produce amorphous material requires the inclusion of large quantities of impurities such as oxygen. Investigating the photoconductivity of these materials has produced some surprising results.

GaN:Mn

The emerging field of spintronics requires development of spin-polarised current sources operating at room temperature. GaN doped with Mn is one candidate material. We have produced a series of nanocrystalline GaN:Mn films grown by ion-assisted deposition, and we find that large quantities of Mn can be incorporated onto the gallium site in this fashion.

Transition metal nitrides

A large number of the transition metal ions can be combined with nitrogen to create materials with a wide variety of properties. We have looked especially at MnN, but we intend to expand this in the near future.

Rare-earth nitrides

Despite theoretical predictions that these materials possess novel electronic structures suitable for use in advanced electronic devices there is little experimental evidence to support the claims. We are working to grow and characterise thin films of a series of these advanced materials. In the Raman laboratory we probe all of these materials through Raman spectroscopy, and we have also used photoconductivity and temperature dependent resistivity measurements to study their properties.

Links to other resources:

• Eurotechnology website on blue lasers
• Spintronics webpage on nanotech-now.com
• Interesting paper on rare earth metals