Advanced Materials & Nanotechnology

Biography

Biography: Noriko Kurose

Abstract

Statement of the Problem: The n-type aluminum gallium nitride (n-AlGaN) vertical field effect transistors on a Si substrate are promising devices for future super high power devices beyond Si, SiC and GaN devices which are currently being developed. The AlN buffer layer is indispensable for the growth of AlGaN epitaxial layer on the Si substrate. However, the AlN is an insulating material and we could not flow current through the buffer layer. We report formation of the conductive AlN buffer layer (hereafter v-AlN) and details of the formation mechanism of the v-AlN.

Methodology: The v-AlN is grown on the Si substrate using metal organic chemical vapor deposition (MOCVD). Al metal dots are grown on the substrate to form Al-Si alloy dots with successive growth of AlN buffer layer. Spontaneous nano size via-holes (hereafter via-holes) are formed in AlN buffer layer due to the surface energy difference of Si and Si-Al alloy. The n-AlGaN is grown on it to fill out the via-holes. The conductive AlN buffer layer with via-holes is formed.

Findings: We have converted the insulating AlN buffer layer to conductive one by forming cluster of via-holes in the buffer layer filled with n-AlGaN during the crystal growth. The size of the cluster and the density are controlled and are 0.2~1µm^Φ and 10⁷~10⁸/cm², respectively. The current flows through these clusters filled with n-AlGaN. The mirror like n-AlGaN epitaxial layer was successfully grown on it. It is confirmed that the vertical resistivity through the conductive AlN buffer layer was 0.2Ω/cm² which is about 10⁴ times smaller than that of conventional AlN.

Conclusion & Significance: We have succeeded in growing the conductive AlN buffer layer on the Si substrate. Our technique and findings open a way to make vertical high power AlGaN FETs, UV-LEDs, UV sensors on the Si substrate and to realize Si on chip devices.