Effect of GaN cap layer grown at a low temperature on electrical characteristics of Al0.25Ga0.75N/GaN heterojunction field-effect transistors

Kao, C. J.; Sheu, J. K.; Lai, W. C.; Lee, M. L.; Chen, M. C.; Chi, G. C.
August 2004
Applied Physics Letters;8/23/2004, Vol. 85 Issue 8, p1430
Academic Journal
This study examined the effect of GaN grown by metalorganic vapor phase epitaxy at low temperature (LT-GaN) on the surface of Al0.25Ga0.75N/GaN heterostructures. Depositing a high-resistivity LT-GaN surface layer on the Al0.25Ga0.75N/GaN heterostructures increased both the sheet carrier concentrations and the electron mobility. This enhancement changed when the LT-GaN high-resistivity layer was removed by high-density-plasma etching. These observations are attributable to the passivation effect, implying that the LT-GaN behaves like a dielectric film, such as silicon dioxide, to passivate the surface states, yielding a different, maybe lower, electronic density of states than that of the Al0.25Ga0.75N free surface. Hall-effect measurement and gate lag measurement were performed on the field-effect transistor devices to clarify the effect of LT-GaN cap layer on Al0.25Ga0.75N/GaN heterostructures.


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