Iron-induced low background impurity and high resistivity GaN films grown by MOCVD on patterned sapphire substrates

Abstract

Electrically insulating GaN epilayers with good crystal quality are essential but challenging for power electronics. Iron (Fe) doping is a valuable method to achieve high resistivity GaN grown by metal–organic chemical vapor deposition (MOCVD). Here, we investigated the impacts of Fe dopants on growth kinetics and electron transition processes in GaN. It is found that the Fe dopants act as surfactants during growth, facilitating the coalescence of GaN and thus effectively limiting the incorporation of oxygen (O) impurities from the substrates into epilayers by 30 times. Meanwhile, the Fe dopants induce a (0/-) transition level, 0.59 eV below the conduction band minimum, which serves as electron traps capturing free electrons and resulting in high resistivity. The relevant mechanism was discussed in detail, and a quantitative model was established, with the consideration of free electron density, donor and Fe concentration, and temperature. Benefit from those, GaN films on patterned sapphire substrates (PSS) with a dislocation density of 1.3 × 10⁸ cm⁻², a resistivity up to 7.4 × 10⁹ Ω∙cm, and free of intentional Fe doping at the surface of the epilayer can be achieved. The clarification of Fe dopants in GaN paves the way for future advanced electronic devices and applications.