Paper AM-ThP2
A New Technique to Make an Insulating AlN Thin Film to be Conductive by Spontaneous via Holes formed by MOCVD and its Application to realize Vertical UV LED on n⁺Si Substrate

Thursday, October 22, 2015, 6:00 pm, Room Hall 3

A new Technique to make an insulating AlN thin film to be conductive by spontaneous via holes formed by MOCVD and its application to realize vertical UV LED on n⁺Si substrate

Noriko Kurose and Yoshinobu Aoyagi

Ritsumeikan University

1-1-1, Noji-higashi, Kusatsu, Shiga, 525-8577, Japan

Abstract

For growing AlGaN epitaxial layer on Si substrate, AlN buffer layer between Si substrate and AlGaN epitaxial layer is indispensable to avoid Si melt-back phenomena coming from direct contact of AlGaN to Si substrate. However, AlN is insulating material even though highly doped. To fabricate vertical type device like vertical UV LED and vertical UV light sensor, the conductive n-AlN is indispensable to insure direct current flow from p-electrode to n-Si substrate. We have succeeded in developing a new technique to grow conductive n-AlN using spontaneous via holes in AlN buffer epitaxial layer grown on n+Si substrate using MOCVD and succeeded in fabricating and operating vertical UV-LED and vertical UV sensor using this technique.

Via holes in AlN buffer layer are spontaneously formed by introducing thin Al layer deposition on the Si substrate. This Al thin layer forms a mask to make spontaneous via holes. Formation of via holes are confirmed by AFM and EDX measurement. Via holes are filled by conductive n-AlGaN and the current flows through these via holes. This current flow through via holes is confirmed by EBIC measurement. The density and the size of via holes are controlled by changing the growth condition of MOCVD. The size of via holes can be varied from 0.1 to 2μm depending on the TMA feeding amount in an initial stage of Al thin layer formation. By growing the p-n junction on the layer with multi quantum wells we have succeeded in vertical LED fabrication (substrate removal free vertical LED, RefV-LED) and operation with direct current flow from p electrode to n⁺Si substrate at the wavelength of 350-400nm with good I-L and I-V performance and near field pattern. The built in voltage of the p-n junction was 3.8V and the break down voltage was more than 35V. The built in voltage is almost same as the band gap of AlGaN used in this RefV-LED. The large breakdown voltage of this device shows us that good p-n junction is formed. Our device can be fabricated without any photoresist processes and is simple to fabricate. These results show us our techniques will open a new window to fabricate a new DUV LED and UV sensor as well.