Master's lecture in Physics - Arnar Már Viðarsson

Master's student: Arnar Már Viðarsson
Title: Investigation of interface and near interface traps in silicon carbide MOS-capacitors using capacitance and conductance techniques
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Faculty: Faculty of Physical Sciences
Advisor: Einar Örn Sveinbjörnsson, Professor at the Faculty of Physical Sciences

Other member of the master's committee: Snorri Þorgeir Ingvarsson, Professor at the Faculty of Physical Sciences

Examiner: Halldór Guðfinnur Svavarsson, Associate Professor at the School of Science and Engineering at Reykjavík University

Abstract

For the past few years silicon carbide (SiC) has become a popular semiconductor for use in high voltage applications such as a power metal oxide semiconductor field effect transistors (MOSFETs). Unfortunately SiC does not come without its flaws. One of the major problems facing scientist is the very low mobility of charge carriers across the channel. This low mobility has been accredited to high density of traps at the interface of the semiconductor surface and the dielectric grown on top. Furthermore near-interface traps can cause leakage over the gate causing undesirable problems, though leakage current is not the focus of this thesis. In this thesis 4H-SiC MOS-capacitors with silicon dioxide (SiO2), dry oxide and annealed with N2O and Na, aluminum nitride - silicon oxide (AlN/SiO2) stack and aluminum oxide (Al2O3) dielectrics are investigated. Their interface and near interface trap densities are determined using Hi/Lo capacitance measurements and distributed circuit model with conductance measurements. The temperature dependence of the Hi/Lo capacitance trap density method is also discussed and how the extracted trap density changes as the measurement temperature is increased or decreased showing slower and faster traps respectively. The findings suggest that SiO2 has the highest density of interface traps while the AlN/SiO2 and Al2O3 have lower densities. The near-interface traps results show that the dry oxide has a density around 1013 cm-2 while the N2O annealed has density of 4 x1012 cm-2 and the best results are found in the Na annealed with density of about 3 x1011 cm-2. The results from the conductance measurements suggest that the AlN/SiO2 and Al2O3 have high gate leakage but SiO2 has little to no leakage but some response from near-interface traps in a form of conductance at high accumulation.