Leakage current and breakdown of HfO2/InGaAs MOS capacitors
Abstract: With the constant downscaling of transistors, silicon as a production material is falling out of favour because of increasing power consumption when the size of devices becomes smaller. Compound materials from group III-V in the table of elements are promising candidates to replace silicon. The aim of this work was to study current-voltage characteristics of a MOS capacitor made of the III-V compound InGaAs. Three samples were produced using atomic layer deposition (ALD) to apply an oxide layer of the high-κ material HfO2 on the InGaAs surface. The thicknesses of these oxide layers were 4 nm, 6 nm and 6 nm where one of the 6 nm samples underwent post-metallisation annealing (PMA). The electric field required to cause a hard breakdown through the oxide was found to be ~0.81 GV/m for the 6 nm annealed sample, ~0.90 GV/m for the 6 nm as deposited sample and ~1.13 GV/m for the 4 nm sample. In all three samples, the breakdown field was widely distributed which indicates an InGaAs-HfO2 interface with a large variation in density of interface traps across the layer. The breakdown field was found to decrease with oxide thickness and PMA treatment, which might be attributed to a percolation path through the oxide being created more easily due to higher polycrystallinity in the thicker oxides. The dominant leakage mechanism at higher biases was determined to be Fowler-Nordheim tunneling and was assumed to be direct tunneling or trap assisted tunneling at low bias. Temperature dependency measurements suggested that trap assisted tunneling gained significance at low bias when the temperature increased.
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