AVS 45th International Symposium
    Nanometer-scale Science and Technology Division Monday Sessions
       Session NS+EM+SS-MoA

Paper NS+EM+SS-MoA7
Low Temperature Cross-Sectional Scanning Tunneling Microscope-Induced Luminescence of GaN

Monday, November 2, 1998, 4:00 pm, Room 321/322/323

Session: Cross-sectional Scanning Tunneling Microscopy of Semiconductors
Presenter: S. Evoy, Cornell University
Authors: S. Evoy, Cornell University
C.K. Harnett, Cornell University
S. Keller, University of California, Santa Barbara
U.K. Mishra, University of California, Santa Barbara
S.P. DenBaars, University of California, Santa Barbara
H.G. Craighead, Cornell University
Correspondent: Click to Email
The GaN system is of interest for applications in the green, blue, and UV spectral regions. Advances in device development have been made in spite of issues such as dislocation densities and defect induced visible luminescence. These issues prompted interest in spatially resolved luminescence studies of the material. Scanning tunneling microscope-induced luminescence (STL) offers nanometer scale resolution and control of the injection bias. In-situ cleaving and cross-sectional imaging is of particular interest for nanoscale luminescence studies of GaN heterostructures and interfaces. We recently reported the first low temperature STL of GaN, and the first STL images of this material. We now report the low temperature cross-sectional STL of MOCVD-grown GaN. Optical interference filters are used for semiquantitative spectral analysis. Room temperature top-view experiments reveal faint visible emission at tip biases above 1.5 V, with no clear evidence of UV luminescence. However, a sharp increase of emission in the 350±35 nm range is observed under liquid He cooling at biases above 3 V. The room temperature visible emission may be related to surface issues, suggesting that low temperature is required for the analysis of intrinsic bulk luminescence. Cross-sectional experiments are performed on in-situ cleaved samples. Incompatible cleaving planes between the GaN and the sapphire produce 200-400 nm wide vertical features, yielding an edge roughness of 30-50 nm. Behavior of luminescence is similar to what was observed in top-view. However, close to the sapphire interface, the 350±35 nm band-edge emission is undetected even at low temperature. Images show strong correlation between the remaining visible emission and the cleaved-induced artifacts. We are currently working on our cleaving technique in order to improve the quality of the edge. The technique will also be applied to the study of GaN heterostructures such as InGaN/GaN quantum wells.