Concentration of point defects in wurtzite AlN: A hybrid functional study

Abstract

Formation energies and concentrations of the most relevant point defects in n-type wurtzite AlN are obtained by first-principle calculations employing a hybrid functional. We show that the incorporation of Si is favoured over O under N-rich growth conditions, but not under Alrich conditions. The triply negatively charged Al vacancy is found to be the defect with the lowest formation energy in n-type AlN and it is therefore expected to be the main compensating acceptor. Under typical physical vapor-phase transport growth conditions, we predict Si concentrations of up to 10 20 cm −3 and net donor concentrations of about 10 18 cm −3 , in good agreement with available experimental data.

Stable and metastable Si negative-U centers in AlGaN and AlN

“…In the neutral charge state d 0 , a Si donor prefers to capture another electron and undergoes a large lattice relaxation, relaxing to its lower-lying negatively charged state DX À according to the process: 10,11 have found two configurations of Si DX donors: a stable DX 1 center with the broken Si-N bond along the c axis and a metastable DX 2 center related to one of three equivalent broken Si-N basal bonds. A more recent calculation predicted no DX-like behavior for Si in AlN and suggested that the n-type conductivity in AlN is caused by the cluster of four Si and an Al vacancy, V Al -4Si, which is predicted to have a formation energy lower than that of the substitutional Si Al donor.…”

The role of the carbon-silicon complex in eliminating deep ultraviolet absorption in AlN

“…Previous studies of silicon in AlN suggest that its presence should shift the Fermi level towards the conduction band. [15][16][17][18][19][20][21][22][23][24][25][26][27][28] The C N defect is only stable in the À1 charge state for values of the Fermi level greater than $2 eV above the valence band maximum. 7,8,29 Thus, the optical signature from C N would not change as the Fermi level increases, and a Fermi-level shift induced by the addition of Si is not sufficient to explain the observed transparency when C À N is the source of the absorption.…”

Optical properties of magnesium doped AlxGa1−xN (0.61 ≤ x ≤ 0.73)

“…Thus facilitated incorporation of compensating donors like Si Al and O N is probable, similar to the case of AlN. 26 We propose the acceptor centers introduced by Mg doping are optically inactive around the band edge, i.e., they mainly contribute to nonradiative centers 23 or cluster. 27 The additionally introduced donors would therefore probably dominate the emission properties of such AlGaN layers.…”