Res of Yoshitake Lab, Kyushu Univ

● Outline

The laboratory devotes itself to education and research on electronic devices for extreme conditions and extremely superior materials for engineering applications. The research is mainly experimentally conducted and the experiment covers the growth of new materials in thin film by physical vapor depositions, laser and plasma plocessing, the structural and optoelectrical evaluations of films, and the fabrication of devices.

● Optical sensors under extreme conditions
Since we succeeded in the formation of ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) films by employing physical vapor depositions, concretely pulsed laser deposition (PLD) and coaxial arc plasma deposition (CAPD), we have extended the research from process developments to applications to electrical devices, as follows.

We have realized the doping of boron and nitrogen for the production of p and n-type conductions accompanied by enhanced carriers densities. Based on the knowledge, we have fabricated heterojunction photodiodes with Si whose conduction type is opposite to that of nanodiamond films, and demonstrated their photovoltaic actions.

From this, we are going to apply UNCD/a-C:H to radiation and DUV sensors. In addition, we will newly study singlecrystalline diamond films with p and n-type conductions and beta-Ga2O3 as component materials. We have started the colaboirative research with AIST and Kyushu Inst Techn.

● Spin sensing

While spintronics has mainly been studied for metals thus far, we are interested in the application of semiconductors to spintronics and related new phenomenon. Particularly, semiconducting beta-FeSi2 that contains Fe atoms and diamond attaract us.
This is a colaboreation research with Kurume College.

● NIR sensing

We have realized the epitaxial growth of beta-FeSi2 films on singlecrystalline Si(111) substrates by sputtering. And based on that, we have fabricated heterojunction photodiodes and demonstrated NIR detection. Owing to large residual carrier densities, the NIR detectivity at room temperature is not so good due to depletion layers hardly expanding into the beta-FeSi2 layer sides. At present, we are make an effort to reduce the residual carrier density.

● Diamond quantum centers

We have realized nano-diamond growth at room tempersture by CAPD, and found that the grain size and density can be enhanced by applying negative biases during the film deposition. From this, we will try to form quantum centers in nanodiamond grains formed by CAPD.

Yoshitake Lab, Kyushu Univ