Methodology for Interface and Defect Assessments in Semiconductors using a combination of synchrotron radiation and electrical measurements

The overall target of the present project is to strengthen the methodology for defect identification in semiconductors and apply it to resolve remaining issues in the field. Two major results may be highlighted. Firstly, a prominent progress has being reached in resolving the long standing issue of either intrinsic or extrinsic origin of the dominating electron trap in Ga2O3 (often labeled as E2 in literature). Our measurements revealed that there are actually two levels in the region of interest ? E2 and a new level labeled as E2*, having the ionization energy very close to that of E2, but exhibiting an order of magnitude larger capture cross section. Importantly, the properties of E2 and E2* were found to be iron- and vacancy-related, respectively. As such, a bit ironically, the long standing literature debate on either extrinsic or intrinsic origin of the carrier trap in question converge accounting for different contributions from E2 and E2* in different experimental conditions. Secondly, a significant effort was dedicated to assess the credibility of an interesting approach to monitor junction capacitance variations induced by the synchrotron radiation. Here, the great potential is in a possibility to collect the information both on electrical characteristics and atomistic structure of the defect simultaneously. Indeed, the feasibility of this novel technique was tested with several occasions at SNBL/ESRF. However, even the initial results were promising, by the time of the report we are still working on the evaluation of the results and it remains to be seen whether we can confirm the expectation or not. All-in-all, as initially proposed, the project comprises an excellent framework for the PhD training and a prominent thesis in field is expected to be defended by Jan-Feb 2019.

This project focuses on developing a novel methodology combining Synchrotron Radiation (SR) studies with advanced electrical characterization techniques in order to study bulk and interface-related defects, enhancing understanding of advanced semiconducto rs. Specifically, Deep Level Transient Spectroscopy (DLTS) is known to be an accurate technique in terms of electrical characteristics of defects, providing however no direct arguments on chemical origin and/or atomic configuration responsible for the DLT S signal. In its turn, when applying SR excitation this missing information may become accessible in the same probing volume of the sample. Having a long tradition in application of DLTS in studies of defects in semiconductors we propose to perform a syst ematic analysis comparing DLTS and SR data for a number of characteristic samples correlating the response, and revealing the origins of debated electronic signatures in bulk semiconductors and selected heterostructures. This activity involves sample synt hesis as well as electrical measurements at the MiNaLab in Oslo and regular visits to the SNBL/ESRF in Grenoble to perform SR measurements. In addition to these conventional "off-line" measurements we plan to investigate a feasibility of "on-line" analysi s when detecting the DLTS signal and, simultaneously, exposing the sample to the SR beam.