Probing Buried Interfaces and Localised Defects Using Hard X-Ray Photoelectron Spectroscopy

Interfaces govern the behaviour of all electronic devices. Herbert Kroemer coined the famous phrase “the interface is the device” in his 2000 Nobel Prize lecture, and we are still applying tremendous effort to understand interfaces in new material generations, with wide-bandgap materials being no exception. If anything, wide bandgap materials are more vulnerable to defect states purely due to their larger bandgap. Understanding gained for the bulk behaviour of semiconductors can often not be extended to the behaviour of materials in structured film stacks were interfaces play a vital role. SiC/SiO₂ is a prototypical wide-bandgap semiconductor/dielectric interface, which represents the challenges faced by many such material systems. A multitude of different defects leads to unacceptably large defect densities exceeding 10¹³ cm^-2 eV^-1 in the vicinity of the conduction band of 4H-SiC. The management of interfacial defects remains a topic of lively discussion and current interest.<br/>This work presents a systematic study of the 4H-SiC/SiO₂ interface in industrially manufactured samples with a particular focus on interface defects and their passivation through nitridation in N₂, NO, NH₃ and NO+NH₃ atmospheres. Using a combination of energy-dependent and angular-dependent hard X-ray photoelectron spectroscopy (HAXPES) a depth profile of both the elemental distribution as well as chemical environments across the interface is obtained. The extracted information on the local chemistry at the interface after the different nitridation processes can be directly correlated to changes in electrical behaviour. This study also showcases a successful combination of both synchrotron-based HAXPES with data from a new generation of laboratory-based spectrometers. Overall, HAXPES is able to deliver a complete picture of this important technological interface and provides a benchmark for the capabilities of this spectroscopic technique for the exploration of buried interfaces in device heterostructures in general.