Model for Low-Temperature Growth of Gallium Nitride

Abstract

A low growth temperature is essential to realize low-cost and large-area GaNbased lighting and display. In this work, through detailed investigation under plasma-assisted molecular beam epitaxy, a physical model for low-temperature growth of GaN under N-rich conditions is proposed based on the fact that the desorption process of Ga adatoms can be ignored and the energy for lattice incorporation of Ga adatoms comes only from active N species. A normalized diffusion length (NDL, a dimensionless parameter) is also introduced to provide further insight: the diffusion rate and diffusion time of Ga adatoms are determined by the growth temperature and N flux, respectively; meanwhile the average distance between Ga adatoms is affected by both Ga flux and N flux. Excellent agreement between theoretical predictions and experimental results validates this model and demonstrates the importance of NDL in optimizing the growth condition. The model and NDL could be applied in growing III-nitrides under N-rich conditions by various lowtemperature growth techniques where group-III adatoms are unable to incorporate into the lattice by their own kinetic energy.

Roles of Atomic Nitrogen/Hydrogen in GaN Film Growth by Chemically Assisted Sputtering with Dual Plasma Sources

“…A much higher atomic nitrogen flux than the Ga flux is generally required for GaN growth because the atomic nitrogen is easily reflected or dissociates from the grown GaN surface. 26 When the atomic nitrogen flux is in excess of the growth rate, the collision probability between migrated Ga and atomic nitrogen is increased, which results in the formation of three-dimensional nuclei with different facets. The diffusion time in eq 2 is then inversely proportional to the rate of atomic nitrogen supply, i.e., τ ∝ v N –1 , as introduced in ref ( 26 ).…”

“… 26 When the atomic nitrogen flux is in excess of the growth rate, the collision probability between migrated Ga and atomic nitrogen is increased, which results in the formation of three-dimensional nuclei with different facets. The diffusion time in eq 2 is then inversely proportional to the rate of atomic nitrogen supply, i.e., τ ∝ v N –1 , as introduced in ref ( 26 ). The small grains grown at N 2 flow rates over 9 sccm without H 2 is presumably attributed to such nuclei.…”

Low-temperature epitaxial technology for flexible optoelectronic devices

“…为研究清低温下生长动力学的过程, 我们通过理论推导构建了低温下原子在衬底表面迁移距离的 理论模型. 结合实验验证该模型能反映温度、Ga 束流和 N 束流等生长条件与材料质量的内在物理关 系, 为低温外延的实验研究提供理论指导 [20] .…”

“…从 NDL 的推导过程可以看出宏观生长工艺参数与微观表面原子迁移的一些关系 [20] , 例如: (1) 目前的生长温度范围约在 400 • C∼600 • C, 在柔性基底的选择上, 柔性金属箔和聚酰亚胺 (polyimide, PI) 衬底等软化温度较高的非单晶衬底能耐受此温度. 若要实现面向各类柔性衬底的外延, 下一 步需要考虑如何进一步降低生长温度.…”

“…对于 GaN 基半导体薄膜, 外延生长温度 一般需要达到 ∼1000 • C. 而通常的柔性衬底, 包括塑料、玻璃和金属薄片, 很难耐受这么高的生长温 度 [18,19] . 为此, 需要将无机光电转换薄膜的生长材料降低到柔性衬底可以承受的范围 [20] . 本文综合 分析了国际上低温外延技术的研究现状, 并着重介绍了本研究团队提出的低温外延方法 --电感应 耦合等离子体金属有机物化学气相外延 (inductive coupled plasma metal organic vapor phase epitaxy, ICP-MOVPE), 包括 ICP-MOVPE 的设计思路、反应腔内等离子体的模拟仿真和该设备进行 III 族氮 化物半导体外延生长的初步结果.…”