Mechanism for Conductivity of AlGaN Semiconductors Determined from EPR Spectra*

Al_xGa_1-xN is an ultrawide band gap (5-6 eV) semiconductor with applications in deep UV LEDs and high-power electronics. In order to enable function and improve performance, UV LEDs need a highly conducting layer which can be achieved with heavily Si-doped Al_xGa_1-xN. The purpose of this research is to develop an understanding of the mechanism for conductivity in Al_xGa_1-xN, x > 0.6, by using Electron Paramagnetic Resonance (EPR) spectroscopy. To achieve this, the line width of the EPR spectra and the electron spin densities were measured in doped Al_xGa_1-xN, with Si concentrations between 10¹⁸-10²⁰ cm^-3.  

In Al_xGa_1-xN:Si, Si acts as a shallow, neutral donor with an EPR g value of about 1.98. The temperature dependence of the donor EPR line width and concentration indicate band formation at lower temperatures (< 40 K) as well as the existence of the structurally relaxed, EPR silent, negative charge state of the donor at higher Al concentrations. In the talk, the analysis of the temperature dependence leading to impurity band formation, as well as the role of EPR in the measurements made will be discussed.