AVS 45th International Symposium
    Electronic Materials and Processing Division Thursday Sessions
       Session EM2-ThA

Paper EM2-ThA9
Near-Surface Variation of Gallium Nitride Cathodoluminescence with Annealing

Thursday, November 5, 1998, 4:40 pm, Room 316

Session: Non-destructive Testing and In-situ Diagnostics
Presenter: T. Levin, The Ohio State University
Authors: T. Levin, The Ohio State University
J. Schäfer, The Ohio State University
A.P. Young, The Ohio State University
L.J. Brillson, The Ohio State University
J.D. MacKenzie, University of Florida, Gainesville
C.R. Abernathy, University of Florida, Gainesville
Correspondent: Click to Email
Er-doped GaN with its promising luminescence yield is of considerable importance for optical communications. However, interfaces can induce significant changes in Er efficiency for optical pumping. Here we report on low energy cathodoluminescence spectroscopy (CLS) to probe the emission of GaN:Er as a function of distance from the semiconductor surface. CLS reveals order-of-magnitude emission variations of Er dopants and related Er-defect complexes vs. depth. Variable incident beam energies (0.5 - 5 keV) provided a strongly depth-dependent excitation from ca. 4 to 40 nm. GaN was grown by metal-organic molecular beam epitaxy at 925°C and doped to 3 x 10@super 18@ cm@super -3@. The primary spectral feature observed was the 0.8 eV (1554 nm) Er emission, which increases by over an order of magnitude with increasing excitation depth. Relative to the broad 'yellow' luminescence between 1.5 and 2.5 eV, which exhibits little or no increase away from the GaN surface, the variation in 0.8 eV emission suggests a depletion of Er within the outer 10 nm. The CLS also reveals three sharp spectral lines at 1.8, 2.2, and 2.3 eV which have been associated with Er 4f transitions from excitation spectroscopy.@footnote 1@ However, the intensities of these features do not scale directly with the 0.8 eV line as a function of depth or processing, but reflect the sensitivity of these additional transitions to near-surface defects and impurities. Annealing the GaN:Er to 500°C for 5 min extends the otherwise bulk emission from these levels to a more uniform distribution extending to within 10 nm of the surface. Further annealing to 700°C promotes even stronger near-surface as well as bulk emission from these lines. However, it produces no significant change in the depth distribution of the 0.8 eV emission but enhances its yield by over a factor of two. Overall, the contrast in intensity variation of specific Er 3+ emission lines with depth reveals the sensitivity of dopant intra-shell transition strengths to near-surface defects. @FootnoteText@ @footnote 1@M. Thaik, U. Hommerich, R.N.Schwartz, R.G.Wilson, and J.M.Zavada, Appl. Phys. Lett. 71, 2641 (1997).