Structure of clean and arsenic-covered GaN(0 0 0 1) surfaces
Abstract The effect of trace arsenic on the growth and surface structure of GaN(0 0 0 1) has been studied. We find that a partial pressure of only 10 −9  Torr of arsenic during molecular beam epitaxial growth significantly modifies the growth kinetics. Such a small background pressure of arsenic leads to an arsenic-terminated surface displaying a 2×2 reconstruction during growth which is absent for the clean surface. First-principles theoretical calculations show that As-terminated surfaces are energetically more favorable than Ga-terminated surfaces for arsenic pressures of 10 −9  Torr, and structural models for the As-adatom 2×2 reconstruction are presented.
Scanning tunneling microscopy of the GaN(000
< ![IGNORE[$\bar{1}$]]) surface

) surface. Four dominant reconstructions have been observed: 1×1, 3×3, 6×6, and c(6×12). The 1×1 structure is formed by annealing the as-grown GaN surface to desorb excess Ga atoms. The higher-order reconstructions are formed by depositing sub-monolayer quantities of Ga atoms onto this 1×1surface. STM images showing the details of the reconstructions are presented and results of quantitative measurements of the number of Ga atoms required to form the various reconstructions are reported. Structural models are compared with the STM data. Reversible order/disorder phase transitions and adatom motion on the GaN surface are discussed.

Studies of Mg-GaN grown by MBE on GaAs(111)B substrates
This paper discusses the growth of Mg-doped GaN samples using a modified Molecular Beam Epitaxy (MBE) method. Our results suggest that the dopant is incorporated from a surface population maintained by the incident Mg flux by a rapid diffusion mechanism. It follows that the chemical concentration will increase with time of growth and that the p-doping level will also increase progressively with film thickness for a given Mg flux. Increasing the Mg flux to the surface results at first in a higher doping density, but this saturates when the Mg surface concentration reaches a finite value.