W e have studied the degradation mechanism of AI-
Cross+ectional transmission electron microscopy (TEM) images from the deteriorated devices reveal the existence of a damaged recess s u f u c e region at the drain side o f t h e device In this dumaged region. a significunt amount of oxygen is detected by energy dispersive xqay spectroscopy (EDX) ana/ysis. The dumuged recess region leads to a reducedzarrier density that results in decreased Imax
The origin of the thermal instability of the AlInAs/GaInAs system is identified and a novel method to recover the thermal degradation is also demonstrated. The thermal diffusion of fluorine into the Si-doped AlInAs layer is found to be the main cause of the electrical deterioration of this system. This finding has led to a method to recover the thermal degradation by purging the fluorine off using the reannealing in the ultrahigh-vacuum condition. This method is now potentially becoming a good candidate as a tip for the AlInAs/GaInAs devices fabrication including laser diode and high electron mobility transistor.
AuGe/Ni/Au alloyed and WSi non-alloyed ohmic contacts are investigated for AlInAs/InGaAs high electron mobility transistors (HEMTs). For the alloyed contact, a contact resistance (R
c) lower than 0.03 Ω mm is obtained at an alloy temperature of 300°C. The value of R
c drastically increases with alloy temperatures above 300°C and exceeds 0.15 Ω mm at 380°C. Auger analysis and analytical cross-sectional transmission electron microscopy have revealed significant outdiffusion of In in the epitaxial layer into the top Au layer and the formation of polycrystalline GaAs in the epitaxial layer, which cause the increase of R
c with alloy temperature. For the refractory WSi non-alloyed ohmic contact, R
c remains lower than 0.1 Ω mm under annealing temperatures up to 380°C. The extrinsic maximum transconductance (g
m) of 600 mS/mm is obtained for the HEMT device with the WSi ohmic contact.
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