Due to their superior properties including wide bandgap, high electron mobility, resistance to thermal degradation and high breakdown field, III-nitrides are well suited for high power and high frequency applications. It is of high interest for IMEC and its industrial collaborators to develop CMOS technology compatible (Al,Ga)N-based heterostructures-on-Si RF and power devices. However, there is a growing concern related to their growth, device reliability and even to their characterization. Owing to the inefficient activation of the dopants, especially of the p-type dopant Mg, and as well as the presence of interface defects arising from lattice mismatch, determination of free carrier concentration, polarization-induced two-dimensional electron gas density and their distribution and their effect on built-in fields are ongoing major issues. As the heterostructure layers go down to few nanometers to 10s of nanometers, it has become essential to be able to probe local electrical properties at the nanoscale. At IMEC with immense expertise in quantitative dopant concentration characterization in Si and III-Vs using Scanning spreading resistance microscopy, the objective of the candidate will be to implement this technique on (p-doped and n-doped) AlGaN based heterostructures and to analyze the effect of local fluctuation in surface barrier height and threading dislocations on current transport. With proper approximation of the surface states, in correlation with direct estimation of the carrier concentration by dC/dV and surface potential across the heterostructures, the three kind of analysis will be combined to reveal the real band structure of the heterostructure.
The goal of this thesis will be to identify and gain understanding into the primary impediments to reliable scanning probe microscopy (SPM) characterization of AlGaN-based heterostructures. SPM measurements will be correlated with other macroscopic electrical characterization techniques including Current-Voltage and Capacitance-Voltage measurements. The student will be trained in advanced electrical SPM techniques, Kelvin Probe Force Microscopy (KPFM), Conductive Atomic Force Microscopy (C-AFM) and Scanning capacitance microscopy (SCM) and will be expected to use them extensively throughout the thesis. In case of necessity for the deeper understanding of the results, complimentary material characterization analysis such as Transmission electron microscopy (TEM) and X-ray photoelectron microscopy (XPS) analysis can be availed. With the guidance of his supervisor, data interpretation and analysis will also be a major part of the thesis/internship. As such, the student will be guided in design of the experiment and understanding the resulting experimental data. A good command of English is required.
Type of project: Internship, Thesis
Duration: 6 months
Required degree: Master of Science, Master of Engineering Science
Required background: Chemistry/Chemical Engineering, Materials Engineering, Nanoscience & Nanotechnology, Physics
Imec allowance will be provided.