Electron Stimulated Desorption of Deuterium from GaN (0001) Surface
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L11.30.1
Electron Stimulated Desorption of Deuterium from GaN (0001) Surface Y. Yang,1 J. Lee, B. D. Thoms, Georgia State University, Atlanta, GA 1 Present Address: University of California, Santa Barbara, CA Abstract Temperature programmed desorption (TPD) was performed on deuterated GaN(0001) surfaces which had been exposed to various doses of 90-eV electrons. TPD of the deuterated surface without electron exposure shows a broad D2 desorption feature with a peak desorption temperature at ~400 °C. Electron exposure results in a decrease in intensity of the desorption peak which is attributed to removal of surface deuterium by electron stimulated desorption (ESD). This removal of deuterium by ESD produces no change in the peak desorption temperature indicating that recombinative desorption is first order in deuterium coverage. I.
Introduction Gallium Nitride (GaN) and its alloys with InN and AlN have been studied because of their applications in red to UV light emitting diodes, lasers, and detectors, as well as hightemperature, high-power, and high-frequency electronic devices [1-3]. Hydrogen is usually present, intentionally or unintentionally, during GaN growth by techniques including MBE, MOCVD and HVPE and during processing such as etching [4 - 14]. The effects of hydrogen on growth and etching are numerous. First, hydrogen introduced in MOCVD is shown to form Mg-H complexes and passivate the dopant. Although this effect can be reactivated by sample annealing, the entire migration path of hydrogen from Mg dopant sites in p-type GaN has not yet been understood. Both experimental and theoretical studies [15 - 21] of hydrogen bonding sites inside GaN conclude that it first migrates from the dopant to the closest defect site then to the second closest defect site and so on. To find if hydrogen can finally migrate to the surface and desorb requires characterizing the reaction of hydrogen on the GaN surface. Earlier desorption studies are very limited [22-24]. Experiments performed in the author’s lab characterized the interaction of hydrogen/deuterium on the GaN (0001) surface by high resolution electron energy loss spectrum (HREELS) [25, 26], ELS [26, 27, 28] and TPD [29]. The surface was determined to be Ga terminated [25]. TPD shows deuterium recombination over a broad temperature range [29]. The broadening of the peaks can be attributed to either a distribution of surface bonding energies or to diffusion during recombinative desorption. This diffusion may involve subsurface hydrogen. Since electron stimulated desorption is a surface sensitive process, studying ESD is useful in discriminating between surface and subsurface species and revealing links between the hydrogen reaction on the GaN surface and bulk migration. Studying ESD efficiency for hydrogen on GaN (0001) may help develop electron stimulated etching techniques on GaN such as low energy electron enhanced etching (LE4) [30] which does not require reactive chemicals or high temperature in contrast to other dry etching techniques [3, 31-33]. It may also
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