スパッタ法を用いて高品質なScAlN薄膜の作製に成功～成長温度の系統的変化が構造特性と電気特性に及ぼす影響を解明～

2025-08-08 東京理科大学,住友電気工業株式会社,東京大学

東京理科大学、住友電気工業、東京大学の共同研究チームは、産業的に汎用性の高いスパッタ法で高品質な窒化スカンジウムアルミニウム（ScAlN）薄膜の作製に成功しました。成長温度を250～750℃で系統的に変化させて解析した結果、温度上昇とともに表面が平坦化し、特に750℃で成長させた膜は最も高品質で、シートキャリア密度が約3倍（1.1×10¹³ cm⁻²）に向上しました。高温成長によりステップフロー成長が促進され、界面の平坦性と結晶均一性が向上、2次元電子ガスの形成効率が高まったと考えられます。一方、電子移動度は全試料で低下し、界面付近の負電荷が原因と推測されます。本成果はGaN系高電子移動度トランジスタ（HEMT）や不揮発性メモリなど次世代高性能デバイスの材料開発に寄与し、低コスト・高品質成膜技術として産業応用の加速が期待されます。

図スパッタ法で基板上に製膜したScAlN薄膜(左)、RHEEDパターン(右上)、およびAFM像(右下)

＜関連情報＞

成長温度がAlGaN/AlN/GaNヘテロ構造上のスパッタエピタキシャルScAlNの構造的および電気的特性に与える影響
Effect of growth temperature on the structural and electrical properties of sputter-epitaxial ScAlN on AlGaN/AlN/GaN heterostructures

Shunsuke Ota;Tomoya Okuda;Kouei Kubota;Yusuke Wakamoto;Takuya Maeda;Takahiko Kawahara;Kozo Makiyama;Ken Nakata;Atsushi Kobayashi
APL Materials Published:August 07 2025
DOI:https://doi.org/10.1063/5.0281540

ScAlN is an attractive barrier material for GaN-based high electron mobility transistors (HEMTs) due to its large polarization and ferroelectricity. However, the influence of growth temperature on its structural and electrical properties remains insufficiently understood. To address this, we investigated the effects of growth temperature on the structural and electrical properties of Sc_0.10Al_0.90N films epitaxially grown on AlGaN/AlN/GaN heterostructures through sputtering. Atomic force microscopy and reflection high-energy electron diffraction revealed that surface morphology and crystallinity improved significantly with increasing growth temperature, with step-flow growth achieved at 750 °C. X-ray diffraction measurements confirmed coherent growth of all ScAlN layers and a decrease in the c-axis lattice constant with increasing growth temperature. Hall effect measurements demonstrated that the sheet carrier density of ScAlN/AlGaN/AlN/GaN grown at 750 °C reached 1.1 × 10¹³ cm⁻², nearly three times higher than that of the structure without ScAlN. The sheet carrier density was lower than that calculated by one-dimensional Poisson–Schrödinger simulations using the theoretical polarization, suggesting the possible existence of negative fixed charges at the ScAlN/AlGaN regrown interface and within the ScAlN layer. These results highlight the critical role of growth temperature in sputter epitaxy of ScAlN and demonstrate the feasibility of using high-quality ScAlN as a barrier layer for GaN-based HEMTs through an industrially compatible process.