Adsorption of atomic and molecular nitrogen at AlN(000-1) surface was investigated by ab initio calculations and thermodynamic analysis. According to earlier works{Kempisty et al. Appl. Surf. Sci. 2020, 532, 147719} in equilibrium with Al vapor, the AlN(000-1) surface is thermodynamically stable in two states: low Al coverage θ_Al ≤ 1/3 ML and high Al coverageθ_Al ≅ 1 ML. In these two cases nitrogen adsorption is completely different. At low Al-covered surface the nitrogen atom is strongly bounded to N surface atom, creates the N₂ admolecule that is finally detached leaving surface vacancy V_N(s). This reaction chain energy gain is positive, $\Delta E_{DFT}^{det}\left(N-N_2\right)=3.50eV$. Therefore, the atomic nitrogen present in plasma assisted molecular beam epitaxy (PA-MBE) fluxes induces the surface decay. N₂ is adsorbed molecularly at the bare surface with the coverage independent energy gain about 1 eV. At the fully Al-covered surface atomic nitrogen is adsorbed in T4 sites with no barrier and large energy gain $\Delta E_{DFT}^{ads-Al}\left(N\right)=8.68eV$. Molecular nitrogen dissociates with the energy gain, dependent on additional N coverage: $\Delta E_{DFT}^{ads-Al}\left(N_2\right)=7.65eV$ at low and $\Delta E_{DFT}^{ads-Al}\left(N_2\right)=2.77eV$ at high, respectively. This change is related to the reduction of electron transfer contribution, caused by Fermi level shift down due to electron transfer from Al to N surface states. The thermodynamic analysis shows incomplete N coverage above the adsorbed Al layer due to the above adsorption energy reduction effect. The resulting incomplete N coverage is responsible for creation of nitrogen vacancies during AlN physical vapor transport (PVT) growth and their coalescence into Al-rich inclusions.

通过从头算计算和热力学分析研究了原子和分子氮在 AlN(000-1) 表面的吸附。根据早期的作品{Kempisty et al. 应用程序 冲浪。科学。 2020 , 532, 147719} 与 Al 蒸气平衡时，AlN(000-1) 表面在两种状态下热力学稳定：低 Al 覆盖率 θ _Al ≤ 1/3  ML和高 Al 覆盖率θ _Al  ≅ 1  ML。在这两种情况下，氮吸附是完全不同的。在低铝覆盖的表面，氮原子与 N 表面原子紧密结合，产生 N ₂分子，最终脱离，留下表面空位 V _N ( s）。这个反应链能量增益是正的，$\Delta {乙}_{DF吨}^{d\mathrm{电子}吨}\left(N-N_2\right)=3.50\mathrm{电子}伏$. 因此，等离子体辅助分子束外延 (PA-MBE) 通量中存在的原子氮会引起表面衰减。N ₂分子吸附在裸露表面，与覆盖无关的能量增益约为1 eV。在完全铝覆盖的表面原子氮吸附在 T4 位点，没有势垒和大的能量增益$\Delta {乙}_{DF吨}^{\mathrm{一种}d秒-\mathrm{一种}升}\left(N\right)=8.68\mathrm{电子}伏$. 分子氮与能量增益解离，取决于额外的氮覆盖：$\Delta {乙}_{DF吨}^{\mathrm{一种}d秒-\mathrm{一种}升}\left(N_2\right)=7.65\mathrm{电子}伏$ 在低和 $\Delta {乙}_{DF吨}^{\mathrm{一种}d秒-\mathrm{一种}升}\left(N_2\right)=2.77\mathrm{电子}伏$在高，分别。这种变化与电子转移贡献的减少有关，这是由于电子从 Al 表面态转移到 N 表面态导致的费米能级下降引起的。热力学分析表明，由于上述吸附能降低效应，吸附的 Al 层上方的 N 覆盖不完全。由此产生的不完整的 N 覆盖是在 AlN 物理蒸汽传输 (PVT) 生长过程中产生氮空位的原因，并且它们合并成富含铝的夹杂物。