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The Characterization and Optimization of GaN Cap Layers and SiN Cap Layers on AlGaN/GaN HEMT Structures Grown on 200 mm GaN on Silicon
Author(s) -
Charles Matthew,
Baines Yannick,
Bouis Renan,
Papon AnneMarie
Publication year - 2018
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.201700406
Subject(s) - materials science , passivation , optoelectronics , high electron mobility transistor , heterojunction , layer (electronics) , transmission electron microscopy , diode , gallium nitride , transistor , nanotechnology , electrical engineering , engineering , voltage
We have studied capping layers for AlGaN‐based high electron mobility transistor (HEMT) structures, looking at different thicknesses of GaN, SiN, and GaN + SiN caps. SiN capping has no effect on the sheet resistance of the layers, as expected from a high quality amorphous passivation layer. GaN cap layers increase the sheet resistance whether combined with a SiN cap or not, a consequence of the polarisation charge present at the GaN/AlGaN interface. For both GaN and SiN caps on their own, we get excellent morphology from only 2 nm thickness, with no degradation for layers up to 10 nm thick. For GaN + SiN caps, we have a speckled morphology with lots of small holes, which transmission electron microscopy (TEM) analysis showed to be linked to holes created in the GaN layers before the deposition of SiN layers. We attribute this to the roughening effect of silane on GaN layers, known in the literature. Upon processing SiN capped and GaN + SiN capped layers into HEMT based heterojunction diode devices, the two have equivalent forward current, but GaN + SiN capping has greatly increased reverse current. We conclude that GaN + SiN is not an appropriate capping layer for AlGaN HEMT based diodes, compared with high quality in situ SiN passivation directly grown on the AlGaN.