ALD gate dielectrics for improved threshold voltage stability in AlGaN GaN MOS-HFETs for power applications

• Published in: Semiconductor science and technology 2015-12, Vol.30 (12), p.125017
• Main Authors: Ramanan, Narayanan, Lee, Bongmook, Misra, Veena
• Format: Article
• Language: English
• Subjects: AlGaN/GaN; atomic layer deposition (ALD); gate dielectrics; high; MOSHFET; power transistors; semiconductor device reliability; semiconductor-insulator interfaces
• ISSN: 0268-1242; 1361-6641
• DOI: 10.1088/0268-1242/30/12/125017

Dielectrics by atomic layer deposition (ALD) are sought after for fabricating AlGaN GaN based metal oxide semiconductor heterojunction field effect transistors (MOS-HFETs) for power applications. The ideal gate dielectric is required to suppress gate leakage and minimize threshold voltage (VT) instability by hosting minimal interface traps. Additionally, with the need for an enhancement mode device, it is preferable if it minimizes VT shift in the negative direction. For the first time, we compare popular ALD dielectrics like SiO2, Al2O3, HfO2 and HfAlO with identical electrical thickness on AlGaN GaN, thereby ensuring identical electrostatic conditions across different dielectrics. High-k ALD dielectrics (HfAlO, HfO2 and Al2O3) are found to suppress gate leakage but host a high density of interface traps with AlGaN, thereby resulting in significant VT instability. ALD SiO2 gate dielectric, annealed in N2 above 600 °C, is a promising gate dielectric candidate which provides the most stable and least negative shift in VT while also substantially suppressing gate leakage below that of an HFET.