AVS 50th International Symposium
    Semiconductors Monday Sessions
       Session SC-MoM

Paper SC-MoM5
Optimizing AlGaN-GaN Heterostructures by MOCVD for Microwave Electronics

Monday, November 3, 2003, 9:40 am, Room 321/322

Session: Heteroepitaxy of Wide Bandgap Semiconductors
Presenter: M.E. Aumer, Northrop Grumman
Authors: M.E. Aumer, Northrop Grumman
D.B. Thomson, Northrop Grumman
D.P. Partlow, Northrop Grumman
R.C. Clarke, Northrop Grumman
S. Cho, University of Maryland
G.W. Rubloff, University of Maryland
R.A. Adomaitis, University of Maryland
Correspondent: Click to Email
GaN-based monolithic microwave integrated circuits (MMICs) for high power, high frequency applications have been reported. Despite impressive initial results, it is clear that realization of the full potential of GaN requires improvement of both the material quality and heterostructure design. To achieve the desired improvements, a set of experiments was performed to uncover material-related factors limiting device performance. Epitaxial films were grown by metalorganic chemical vapor deposition (MOCVD) and characterized by photoluminescence (PL), x-ray diffraction (XRD), x-ray reflectance, reciprocal space mapping, Hall effect, and contactless resistivity mapping. Wafer maps of the data illustrate correlations such as a relationship between substrate rocking curve linewidth and AlGaN-GaN interface roughness. Also, it was found that nucleation layer microstructure has a large effect on GaN crystallinity and HFET performance. Optimization of the nucleation layer resulted in a reduction of the screw and edge dislocation density from over 5x10@super8@ cm@super-2@ to less than 5x10@super7@ cm@super-2@. The defect reduction was not accompanied by a significant improvement in the sheet resistance of the channel region, suggesting that neither the electron density nor the low-field mobility were directly affected; however, devices fabricated on such wafers exhibited improved breakdown voltage and output resistance, both of which are important for MMICs. Results from short-loop fabrication of HFETs will be presented to illustrate the impact of material properties as well as heterostructure design on device properties such as I@subDSS@, transconductance, and breakdown voltage.