Theoretical study of adatom stability on polar GaN surfaces during MBE and MOVPE
Theoretical study of adatom stability on polar GaN surfaces during MBE and MOVPE
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DOI：
10.1016/j.apsusc.2019.144205
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发表时间：
2020-02-01
影响因子：
6.7
通讯作者：
Kangawa, Y.
中科院分区：
文献类型：
--
作者：
Inatomi, Y.;Kangawa, Y.
GaN具有优良的功率器件上级性能，是实现节能型社会的关键材料。了解晶体生长的物理过程可以加速GaN基器件的发展。已经有多个理论研究调查在生长期间从GaN以最小能量的表面重建。然而，尽管最稳定的重建在表面上占主导地位，但由于熵效应，其他重建也可能出现。考虑到GaN的生长速率通常受到Ga前体流速的限制，Ga吸附重构的出现概率应该很小。很少有人知道这样的小重建的相对稳定性。在这里，我们提出了一个新的计划来计算重建的出现概率。计算结果表明，在金属有机气相外延（MOVPE）过程中，随着H2分压的降低，GaN（0 0 0 1）表面的N密度增加，Ga密度降低，形成了高富N表面.相反，对于GaN（0 0 0 - 1），N和Ga密度都随着H-2分压的降低而增加，从而导致富Ga表面。结果很好地解释了报道的极性GaN的生长特性。
GaN is a key material for realizing an energy saving society owing to its superior properties for power devises. Understanding the physics of the crystal growth can accelerate the development of GaN-based devices. There have been multiple theoretical studies that investigate the surface reconstructions with minimum energy from GaN during growth. However, although the most stable reconstruction is dominant on the surface, other reconstructions could also appear probabilistically due to the entropic effect. Considering the growth rate of GaN is typically limited by the Ga precursor flow rate, the appearance probability of Ga-adsorbed reconstruction should be small. Little is known about the relative stabilities of such minor reconstructions. Here, we propose a new scheme to calculate the appearance probabilities of reconstructions. Our calculation reveals that the N density increases and Ga density decreases on GaN(0 0 0 1) during metalorganic vapor phase epitaxy (MOVPE) with decreasing H-2 partial pressure, resulting in a highly N-rich surface. In contrast, for GaN(0 0 0-1), both N and Ga densities increase with decreasing H-2 partial pressure, resulting in a Ga-rich surface. The results well explain the reported growth characteristics of polar GaN.