Group Page

Professor
Ph.D., Oklahoma State University
Study of surfaces with important catalytic and semiconductor properties

Group III-Nitride thin films have sparked interest due to their desirable electrical, optical, dielectrical, and acoustical properties. AlN and GaN are two semiconductors currently being studied as promising materials for blue/UV light emitting diodes because of their wide band gap, high melting point and high luminescence intensity. The chemical and thermal stability of AlN, coupled with its high resistivity, makes it a potential candidate for use as passivation layers in semiconductor devices. Applications using AlN and GaN semiconductors range from high density optical data storage and full color video-screens to simple traffic lights.

Our lab is growing AlN films incorporated with lanthanide or transition metals. Crystalline films are grown by rf magnetron sputtering at temperatures between 600 and 1000 degrees Celsius. Lower temperature growth (300 degrees Celsius) produces amorphous films that resist decomposition or crystallization even when heated in excess of 1000 degrees Celsius. The optical properties of these films are characterized using cathodoluminescence, photoluminescence, and electroluminescence spectroscopy. The film morphology is probed with x-ray diffraction, optical and scanning electron microscopy, infrared microscopy and Raman scattering spectroscopy.

We have recently discovered that it is possible to dope amorphous AlN with transition or lanthanide metals and make them luminescent active without disturbing the amorphous character of the AlN host. Different metals emit different colors of light depending upon the metal ion properties and the crystal fields of the AlN host. Blue and red light is emitted from Cu and (Mn, Cr, Eu) respectively while green light is emitted from (Tb, Er). This new type of phosphor material can be incorporated into a light-emitting device.

Unfortunately, this type of film must be heated between 700-1000 degrees Celsius in order to activate the emission of visible light. This treatment precludes using substrate that have a low melting point, i.e., flexible plastics. Very recently we have found that contaminating the films with a small amount of oxygen during room temperature growth produces films that are luminescent active in the visible region. This breakthrough means that light-emitting devices can be fabricated on flexible plastics using amorphous III-V materials incorporated with lanthanide metals. Already, we have made light-emitting devices using Tb and Eu and have patterned the phosphor using standard lithographic techniques.

Caldwell, M. L.; Van Patten, P. G.; Kordesch, M.E.; Richardson, H. H., Visible Luminescent Activation of Amorphous AlN:Eu Thin-Film Phosphors with Oxygen, submitted to MRS Internet Journal Nitride Semiconductor Research , 2001 .

Martin, A. L.; Spalding, C. M.; Dimitrova, V.I.; Van Patten, P. G.; Caldwell, M. L.; Kordesch, M. E.; Richardson, H. H., Visible Emission from Amorphous AlN Thin-film Phosphors with Cu, Mn, or Cr. Journal of Vacuum Science and Technology A 2001 , 19(4), 1894-1897.

Martin, A. L.; Caldwell, M. L.; Kordesch, M. E.; Spalding, C. M.; Van Patten, P. G.; Richardson, H. H., Luminescence Properties of Amorphous AlN Thin Film Phosphors Incorporated with Mixtures of Tb, Cu or Cu, Cr. Material Research Society Symposium Proceedings 2001 , 639, G6.5.1-6.

Caldwell, M. L.; Martin, A. L.; Spalding, C. M.; Van Patten, P. G.; Kordesch, M. E.; Richardson, H. H., Visible Emission from Thin-Film Phosphors of Amorphous AlN:Cu, Mn, and Cr, submitted . Material Research Society Symposium Proceedings 2001 , 639, G6.6.1-6.

Spalding, C. M.; Caldwell, M. L.; Dimitrova, V. I.; Martin, A. L.; Kordesch, M. E.; Richardson, H. H.; Van Patten, P. G.; Characterization of the Mechanism of Activation for Visible Luminescence in Rare-earth Doped Crystalline and Amorphous AlN Thin Films, submitted to . Material Research Society Symposium Proceedings 2001 , 639, G6.22.1-6.