Abstract
Control of leakage currents in the buffer layers of GaN based transistors on Si substrates is vital for the demonstration of high performance devices. Here, we show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage. Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL. We also show that when 2D growth of the AlGaN SRL is maintained a significant increase in the breakdown voltage can be achieved even in much thinner buffer layer structures. These results demonstrate the importance of controlling the morphology of the high electron mobility transistor buffer layer as even at a very low density the leakage paths identified would provide leakage paths in large area devices.
Highlights
Over the last two decades, GaN-based high electron mobility transistors (HEMTs) have been attracting growing interest for power switching applications due to their superior electrical characteristics including high breakdown voltages, low on-resistances, and fast switching.[1,2] challenges such as current collapse and buffer breakdown still exist and restrict the device’s ultimate performance.[3]
We show that the growth conditions during the metal organic chemical vapour deposition growth of the graded AlGaN strain relief layers (SRLs) can significantly influence the vertical leakage
Using scanning capacitance microscopy, secondary ion mass spectrometry, and transmission electron microscopy, we investigate the origins of leakage paths and show that they result from the preferential incorporation of oxygen impurities on the side wall facets of the inverted hexagonal pyramidal pits which can occur during the growth of the graded AlGaN SRL
Summary
Over the last two decades, GaN-based high electron mobility transistors (HEMTs) have been attracting growing interest for power switching applications due to their superior electrical characteristics including high breakdown voltages, low on-resistances, and fast switching.[1,2] challenges such as current collapse and buffer breakdown still exist and restrict the device’s ultimate performance.[3]. We study the impact of the growth conditions for the strain relief layer (SRL) on vertical leakage in GaN HEMT device structures grown on p-type silicon substrates. The impact that the morphology during growth has on the structure of the buffer layer is examined by plan view scanning transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDX) analysis to give compositional information. This structural information about these layers is used to explain the difference in the vertical leakage currents measured on two HEMT structures
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