| dc.description.abstract | The primary objective of this research is to optimize the epitaxial structure
of high-power gallium nitride high electron mobility transistors (GaN HEMTs)
in order to enhance their vertical breakdown voltage, electrical conductivity,
and dynamic resistance performance. Initially, the introduction of a superlattice
structure increased the vertical breakdown field of the epitaxial layer from 1.75
MV/cm to 1.94 MV/cm. Through further optimization, the ideal carbon doping
concentration in the GaN buffer layer was identified, eventually raising the
vertical breakdown field of the epitaxial layer to 2.28 MV/cm following the
refinement of the superlattice structure.
Using this optimized design, the fabricated high-power GaN HEMT
devices, incorporating a p-type GaN and a suitable AlGaN barrier layer,
demonstrated a breakdown voltage of 1351 V@1 mA/mm (1600 V@1 mA/mm,
substrate floating), a threshold voltage of 1.2 V, and a specific on-resistance of
1.95 mΩ-cm2 for a gate-to-drain distance (Lgd) of 13 μm, achieving
internationally competitive performance standards.
Additionally, modifying the aluminum content and thickness of the back
barrier layer proved effective in reducing the electric field variation in the
channel layer, thereby substantially improving the channel conductivity. When
the aluminum content in the back barrier was decreased from 6 % to 2 %, and
its thickness increased from 100 nm to 150 nm, the drop in channel conductivity
under a substrate negative bias of -100 V decreased from 78 % to 38 %.
However, while the lower aluminum content and thicker back barrier improved
conductivity under negative bias, the dynamic resistance increased. In this
study, a back barrier structure with 6 % aluminum content and 50 nm thickness reduced the dynamic resistance from 7.54 times to 4.3 times under a VDSQ of
80 V, considerably improving dynamic characteristics.
In summary, the novelty of this work lies in the precise design of
superlattice structures and back barrier layers, which successfully enhance the
vertical breakdown voltage, conductivity, and dynamic resistance performance
of GaN HEMT devices. The study also introduces strategies for flexible back
barrier design tailored to specific application needs, balancing conductivity and
dynamic resistance to ensure device stability and efficiency under high-power
operation conditions. | en_US |