Kavli Affiliate: Grace Xing
| First 5 Authors: Eungkyun Kim, Yu-Hsin Chen, Naomi Pieczulewski, Jimy Encomendero, David Anthony Muller
| Summary:
AlN has the largest bandgap in the wurtzite III-nitride semiconductor family,
making it an ideal barrier for a thin GaN channel to achieve strong carrier
confinement in field-effect transistors, analogous to silicon-on-insulator
technology. Unlike SiO$_2$/Si/SiO$_2$, AlN/GaN/AlN can be grown fully
epitaxially, enabling high carrier mobilities suitable for high-frequency
applications. However, developing these heterostructures and related devices
has been hindered by challenges in strain management, polarization effects,
defect control and charge trapping. Here, the AlN single-crystal high electron
mobility transistor (XHEMT) is introduced, a new nitride transistor technology
designed to address these issues. The XHEMT structure features a pseudomorphic
GaN channel sandwiched between AlN layers, grown on single-crystal AlN
substrates. First-generation XHEMTs demonstrate RF performance on par with the
state-of-the-art GaN HEMTs, achieving 5.92 W/mm output power and 65% peak
power-added efficiency at 10 GHz under 17 V drain bias. These devices overcome
several limitations present in conventional GaN HEMTs, which are grown on
lattice-mismatched foreign substrates that introduce undesirable dislocations
and exacerbated thermal resistance. With the recent availability of 100-mm AlN
substrates and AlN’s high thermal conductivity (340 W/m$cdot$K), XHEMTs show
strong potential for next-generation RF electronics.
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