InAs and high-k oxides, a scanning tunnelling study of their interfaces

Abstract: In order for semiconductor materials to be suitable for implementation in new and progressive devices they have to be of better electronic characteristics than currently used materials, and maintain these once treated and put into action. It is important to verify that bulk characteristics are not hindered at the surface when a given semiconductor is put in contact with another material due to necessity. In particular, one may want to isolate the surface of a semiconductor from the ambient, and implement artificially grown insulators, such as some types of oxides, to do just this. It is then crucial to verify that the semiconductor’s value is not compromised by it being put into contact with the insulator. III-V semiconductors are very promising, in terms of electronic characteristics, when it comes to application in progressive devices. However, they are known to have defect-rich native oxides, which means that a number of different surface treatment techniques are required to replace them with better ones and ultimately allow for III-V implementation. Moreover, one has to make sure that interface quality between III-V semiconductors and artificially grown oxides is appropriate. In this project, InAs (one of many III-V semiconductors) surfaces are considered, alongside the interfaces between them and thin HfO2 (hafnium oxide, a highly insulating material) layers. Sample preparation is realised through annealing (under atomic hydrogen flow) for surface cleaning, and atomic layer deposition (ALD) for controlled deposition of insulating oxide. The main tools at hand for sample analysis consist in scanning tunnelling microscopes, hence the use of scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) to record data. All in all, it is deduced that electron states altering the standard InAs band structure are at times present at the interface between semiconductor and oxide, hinting at creation of imperfect samples. Nevertheless, the work carried out in this project should open the door for further investigation on what materials and laboratory procedures work best and will eventually meet optimal interface conditions.