Development of reactive Czochralski method for nitride crystal growth

2021 Fiscal Year Final Research Report

• Project/Area Number: 20K21071
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 26:Materials engineering and related fields
• Research Institution: Tohoku University
• Principal Investigator: Fukuyama Hiroyuki 東北大学, 多元物質科学研究所, 教授 (40252259)
• Project Period (FY): 2020-07-30 – 2022-03-31
• Keywords: 熱力学 / 結晶成長 / 窒化物半導体 / 電磁浮遊法

Outline of Final Research Achievements

The crystal growth diagram for aluminum nitride (AlN) crystal has been built to develop the reactive Czochralski method using Ni-Al fluxes based on thermodynamic considerations. The driving force of AlN formation was displayed in the diagram as a function of temperature, N2 partial pressure and flux composition. The crystal growth process can be designed near the equilibrium condition by using the diagram. Based on the diagram, in-situ observations of AlN growth were conducted using an electromagnetic levitation technique, and optimum growth condition was obtained. Finally, AlN growth experiments were conducted with the optimum driving force condition using Ni-Al fluxes. The reactive Czochralski method was demonstrated to be a promising method for AlN crystal growth from viewpoints of growth rate and crystal quality.

Free Research Field

材料プロセス

Academic Significance and Societal Importance of the Research Achievements

幅広い紫外領域をカバーするAlGaN系紫外発光素子の内部量子効率は、サファイア基板とAlGaN層の格子不整合に起因する多数の貫通転位のために低く抑えられている。本研究成果は、AlN単結晶の新たな成長方法を提案するものであり、サファイア基板をAlN基板で置き換えることによって、飛躍的な格子整合性の向上、ひいては、内部量子効率の向上につながることが期待される。AlN単結晶は、原料紛体を2000℃以上の高温で昇華させ、温度勾配下で再結晶させて単結晶を得る昇華法により製造されているため、極めて高価で、市場への供給も不安定である。本研究は、昇華法に代わる低コストな結晶成長法としても期待されている。