Chapter 4 - Magnetic resonance studies of defects in GaN and related compounds

Abstract

The term magnetic resonance means resonance absorption of electromagnetic radiation at microwave (radiofrequency) range by paramagnetic defect center present in the investigated crystal with magnetic field of values characteristic for the center applied. This chapter reviews the magnetic resonance studies of defects in nitrides. It also summarizes the results of research performed by different scientific groups. The investigated crystals were grown by different techniques—bulk material by high pressure method, epitaxial layers by molecular organic chemical vapor deposition (MOCVD), and microcrystalline powder by ammonothermal method. Bulk nitride crystals were obtained for ESR studies. ESR experiments are performed to determine the nature, symmetry, and environment of paramagnetic defects in crystals. The ESR signal due to shallow donor characteristic for MOCVD grown GaN was well established. The other magnetic resonance technique, called optically detected magnetic resonance (ODMR), allows studying excited states of defects. The ODMR experiment is useful in detection of emission changes due to microwave absorption at the excited states in applied magnetic field. ODMR technique has been successfully used to study defects in different semiconductors, such as II–VI, III–V, and amorphous Si.