High n-type conductivity and carrier concentration in Si-implanted homoepitaxial AlN

Abstract

We demonstrate Si-implanted AlN with high conductivity (>1 Ω−1 cm−1) and high carrier concentration (5 × 1018 cm−3). This was enabled by Si implantation into AlN with a low threading dislocation density (TDD) (<103 cm−2), a non-equilibrium damage recovery and dopant activation annealing process, and in situ suppression of self-compensation during the annealing. Low TDD and active suppression of VAl-nSiAl complexes via defect quasi Fermi level control enabled low compensation, while low-temperature, non-equilibrium annealing maintained the desired shallow donor state with an ionization energy of ∼70 meV. The realized n-type conductivity and carrier concentration are over one order of magnitude higher than that reported thus far and present a major technological breakthrough in doping of AlN.

Shallow donor and DX state in Si doped AlN nanowires grown by molecular beam epitaxy

“…1. At lower temperatures, an ionization energy of 75 meV is extracted which is consistent with the shallow donor state of Si in AlN 34,35 and predicted by the hydrogenic model.…”

“…Consistently, photoconductivity experiments performed by Zeisel and coworkers have demonstrated the presence of DX states in Si:AlN layers 33 . Recently, shallow donors in AlN were reported in Si-implanted AlN after annealing at rather low temperature preventing Si atoms to relax to the stable DX state 34,35 .…”

Recent Advances in Fabricating Wurtzite AlN Film on (0001)-Plane Sapphire Substrate

“…They realized Si doping of homoepitaxial AlN by combining ion implantation and non-equilibrium annealing process at relatively low temperature (1200 • C). A defect Quasi Fermi Level (dQFL) control method was adopted to suppress self-compensation [123]. H. Ahmad et al reported a recordhigh bulk hole concentration of 3.1 × 10 18 cm −3 in a beryllium-doped AlN/sapphire via metal modulated epitaxy (MME) in an MBE system [124].…”

Temperature dependence of electrical characteristics of Si-implanted AlN layers on sapphire substrates

“…The conditions close to thermal equilibrium, such as epitaxial growth and hightemperature annealing, favor forming a DX − center with E d = 250-320 meV, [38][39][40][41] while a non-equilibrium process, such as ion implantation, can increase the population of d 0 . 36,42,43) N d , N a , and E d can be estimated from the charge neutrality conditions for a non-degenerate n-type semiconductor, i.e.…”

“…Implantation at high temperature and a long annealing time would reduce the implantation-induced defects and make more Si atoms act as donors by substituting at Al sites, leading to a high N d /[Si], low N a /N d , and low ρ c . Also, reducing the annealing temperature to 1200 °C-1300 °C may enhance the formation of d 0 , 36,42,43) leading to a high electrical activation ratio and low R s .…”