Thermodynamic model for metalorganic vapor-phase epitaxy of N-polar group-III nitrides in step-flow growth mode: Hydrogen, competitive adsorption, and configuration entropy
Thermodynamic model for metalorganic vapor-phase epitaxy of N-polar group-III nitrides in step-flow growth mode: Hydrogen, competitive adsorption, and configuration entropy
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DOI：
10.1103/physrevmaterials.3.103404
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发表时间：
2019-10-31
影响因子：
3.4
通讯作者：
Hanada, Takashi
中科院分区：
文献类型：
--
作者：
Hanada, Takashi
基于Burton，Cabrera，and Frank（BCF）理论，建立了N极性（000（1）over bar）二元III族氮化物（AlN，GaN，InN）分步流动生长模式下金属有机物气相外延（MOVPE）的热力学模型.第III族吸附原子的覆盖率在与氢气的竞争吸附下进行了分析评价，氢气用作载气或在MOVPE期间从NH3源气体解离。N-极性III族氮化物表面上的III族和H吸附原子的化学势使用与氮化物的表面N原子的各自的键能和吸附原子的振动频率来建模。共吸附的第III族和H吸附原子的覆盖率计算使用这些化学势的Langmuir吸附等温线。III族吸附原子的组态熵弥补了热力学模型与BCF理论之间的差距。在热力学中，第三族吸附原子的覆盖度起着类似于第三族气体分压的作用。根据源之间的吉布斯能量平衡条件，计算了III族吸附原子的平衡覆盖率和NH3气体的平衡压力（III族吸附原子和NH3气体分子）和产物（第III族氮化物和3/2 H-2气体分子）和第III族和N并入到步骤扭结之间的速度平衡。通过该方法获得极性GaN和InN。在所研究的二元III族氮化物中，AN的生长几乎不受H-2气体压力的影响，GaN的生长受到H-2气体压力的良好控制，而InN的生长受到H-2气体的强烈抑制。使用的增长模型和估计的增长参数的NH3/第三组流量比为最大的产品/成本和最小的材料浪费的标准进行了论证。还研究了切角对相邻衬底生长速率的影响。
A thermodynamic model for metalorganic vapor-phase epitaxy (MOVPE) of the N-polar (000 (1) over bar) binary group-III nitrides (AlN, GaN, and InN) in the step-flow growth mode is proposed based on the Burton, Cabrera, and Frank (BCF) theory. The coverages of the group-III adatoms are thermodynamically evaluated under competitive adsorption with hydrogen, which is used as a carrier gas or dissociated from the NH3 source gas during MOVPE. The chemical potentials of the group-III and H adatoms on N-polar group-III nitride surfaces are modeled using the respective bond energies with the surface N atoms of the nitride and the vibrational frequencies of the adatoms. The coverages of the coadsorbed group-III and H adatoms are calculated using the Langmuir adsorption isotherm with these chemical potentials. The configuration entropy of the group-III adatoms bridges the gap between the thermodynamic model and the BCF theory. The coverage of the group-III adatoms plays a role like partial pressure of the group-III gas in the thermodynamics. The equilibrium coverage of the group-III adatoms and the equilibrium pressure of the NH3 gas are evaluated from the conditions of Gibbs energy balance between the sources (group-III adatom and NH3 gas molecule) and products (group-III nitride and 3/2 H-2 gas molecules) and of speed balance between group-III and N incorporation into step kinks Fair agreements with the experimentally optimized growth conditions for MOVPE of N-polar GaN and InN are obtained by this method. Among the examined binary group-III nitrides, AN growth is hardly affected by H-2 gas pressure, GaN growth is controlled well by H-2 gas pressure, and InN growth is strongly inhibited by H-2 gas. A criterion for selecting the NH3/group-III flow ratio for maximum products/cost and minimum waste of the materials is demonstrated using the growth model and the estimated growth parameters. The offcut angle dependence of the growth rate on the vicinal substrates is also investigated.