Chemistry Graduate Seminar presented by Professor Ratnakar Palai, , University of Puerto Rico Río Piedras;Hosted by: Prof. Arthur D. Tinoco

Title: Rare earth doped III-nitride semiconductor nanostructures for spintronic and optoelectronic applications

By: Ratnakar Palai
Department of Physics, University of Puerto Rico, San Juan, PR, USA
Email: r.palai@upr.edu

Abstract: III-Nitride semiconductors and their alloys (InN, GaN, AlN, and InGaN) are promising materials for applications in electronics, photonics, and photovoltaics. Currently a great deal of attention is being focused on adding spin degree-of-freedom into semiconductor to create a new area of solid-state electronics, called spintronics. In spintronics not only the current but also its spin state is controlled. Such materials need to be good semiconductors for easy integration in typical integrated circuits with high sensitivity to the spin orientation. In the past, most of the attention on ferromagnetic semiconductor has focused on the GaMnAs and InMnAs. Despite of many years of intense research the highest Curie temperatures (Tc) reported were far below the room temperature, about 185K for GaMnAs and ~35 K for InMnAs. The major material challenge is to magnetize and stabilize semiconductors with room temperature ferromagnetic ordering without significantly affecting the physical properties of semiconductors.

Rare-earth (RE) elements play an important role in many functional materials and exhibit interesting magnetic and optoelectronic properties. Due to their highly localized 4f electrons the direct f-f interactions between the neighboring rare-earth atoms are very weak. This produces larger magnetic moments in 4f REs than 3d transition metals. Most of the earlier works on dilute magnetic semiconductor (DMS) were focused on TM doped GaN and ZnO and week magnetization has been reported with few percentage (< 5%) of doping. In order to enhance the magnetization, higher percentage of TM doping in ZnO and GaN was investigated but it was found that the magnetization related to the clustering or precipitation of TM ions. Since REs have higher magnetic moment than TMs, we expect to achieve higher magnetization with a few percentage of RE doping.

Thin films and nanorods of RE (Yb and Er) doped GaN and InGaN were grown using molecular bean epitaxy (MBE). The samples show many interesting and enhanced luminescent properties compared to undoped samples with room temperature ferromagnetism. The talk will be focused on fabrication, magnetic (SQUID and MFM), luminescence (PL and CL)), and spectroscopic (XPS) properties of Yb and Er doped GaN and InGaN semiconductor nanostructures.