IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Monday Sessions
       Session SC-MoA

Invited Paper SC-MoA1
The Influence of Active Nitrogen Species and Substrate Polarity on the Growth and Doping of GaN Grown by RF Plasma-assisted Molecular Beam Epitaxy

Monday, October 29, 2001, 2:00 pm, Room 124

Session: GaN Surfaces, Interfaces, and Devices
Presenter: T.H. Myers, West Virginia University
Authors: T.H. Myers, West Virginia University
A.J. Ptak, West Virginia University
L.T. Romano, Xerox Palo Alto Research Center
Correspondent: Click to Email
Growth of GaN by molecular beam epitaxy (MBE) is typically limited by increased desorption of Ga from the growing surface. We will report on the relative reactivity of the various active nitrogen species produced by rf plasma sources: low and high energy ions, atoms and metastables. Studies of growth rate as a function of temperature suggest the GaN surface is prone to "attack" by neutral and ionic atomic nitrogen above 700oC, promoting decomposition. This leads directly to the observed lower than expected temperature for a significant decrease in growth rate, while this decrease is not observed when the active nitrogen flux consists primarily of nitrogen metastables. Dramatically improved electrical properties are observed in epilayers grown using nitrogen metastables. Similar to most compound semiconductors, GaN lacks inversion symmetry that leads to different chemical terminations on different crystal planes. The two most common surfaces, the (0001) (or Ga-polar) and the (000-1) (or N-polar) surfaces exhibit quite different properties. Results illustrating the differences in basic growth kinetics related to surface polarity will be presented. Surface polarity also has a pronounced influence on doping. A pronounced dependence of Mg incorporation on surface polarity was observed in a series of Mg step-doped epitaxial GaN layers. Measurements indicate surface accumulation of Mg occurs during growth, with stable accumulations of close to a monolayer of Mg on the Ga-polarity surface. This surface layer can cause surface inversion to occur. Beryllium incorporation was also studied for both Ga-polarity and N-polarity GaN. Unlike magnesium, surface polarity-related incorporation differences were less pronounced for Be. Preliminary results, however, indicate a strong dependence of compensation, e.g. point defect formation, on surface polarity. Polarity related issues for O-incorporation will also be discussed.