AVS 46th International Symposium
    Surface Science Division Tuesday Sessions
       Session SS-TuP

Paper SS-TuP26
Extremely Efficient Electron Stimulated Desorption of Hydrogen from GaN(0001)

Tuesday, October 26, 1999, 5:30 pm, Room 4C

Session: Poster Session
Presenter: V.J. Bellitto, Georgia State University
Authors: V.J. Bellitto, Georgia State University
B.D. Thoms, Georgia State University
D.D. Koleske, Naval Research Laboratory
A.E. Wickenden, Naval Research Laboratory
R.L. Henry, Naval Research Laboratory
Correspondent: Click to Email
To achieve high etch rates and anisotropy during etching of GaN, high temperatures, reactive chemicals, and/or high ion energies are required. The use of electron or photon stimulated processes for etching may be one method to avoid the use of reactive chemicals, damage produced by high ion energies, and materials limitations imposed by high temperatures. Electron stimulated desorption (ESD) of H from GaN(0001) has been observed and characterized using electron energy loss spectroscopy (ELS). Bombardment with 90 eV electrons produces a reversal of H induced changes in the ELS data at 3.5, 6.6, and 11.7 eV. We attribute the electron-stimulated desorption of hydrogen from surface Ga-H to be responsible for these reversals. The reversal of H induced changes to ELS was monitored versus electron exposure to determine the ESD cross section. We measured a cross section for ESD of H of 2 x 10 @super -17@ cm@super 2@ with a reduction of ~3 for the ESD of D to 7 x 10 @super -18@ cm@super 2@. The cross section for the ESD of H from GaN(0001) is 2 to 4 orders of magnitude greater than reported on Si surfaces. On GaN the cross section for ESD of D is ~3 times smaller than for H, while on Si(100) the ESD of D is ~50 times less than for H. Assuming the ESD of H from GaN(0001) occurs through an electronically excited state, as in the Menzel-Gomer-Redhead (MGR) model, the presence of a large cross section and small isotope effect would indicate slow quenching of the excited electronic state. In general, long-lived surface electronic excitations would result in enhanced efficiencies for electron- or photon-stimulated processes. This extremely fast ESD of H also has consequences for electron spectroscopies (LEED & ELS) of H/GaN using similar electron energies and current densities. For example, under the conditions used in these experiments (90 eV, 33 µA/cm@super 2@), 34 % of the surface H is removed in the first minute of electron exposure. In essence, the H is removed from GaN(0001) more quickly than many electron spectroscopies can be performed.