Oxide Trapping in the InGaAs–$\hbox{Al}_{2} \hbox{O}_{3}$ System and the Role of Sulfur in Reducing the $ \hbox{Al}_{2}\hbox{O}_{3}$ Trap Density

Trap spectroscopy by charge injection and sensing method was applied to the
$\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}{-}\hbox{Al}_{2}\hbox{O}_{3}$
system, yielding the spatial and energetic distribution of the traps inside the
$\hbox{Al}_{2}\hbox{O}_{3}$
layer. The trap density inside the atomic-layer-deposited (ALD)
$\hbox{Al}_{2}\hbox{O}_{3}$
layer was found to be significantly reduced by
$(\hbox{NH}_{4})_{2}\hbox{S}$
treatment of the InGaAs surface prior to the
$\hbox{Al}_{2}\hbox{O}_{3}$
deposition. Indium concentration inside the
$\hbox{Al}_{2}\hbox{O}_{3}$
layer was found to be reduced once the InGaAs surface is
$(\hbox{NH}_{4})_{2}\hbox{S}$
treated prior to the
$\hbox{Al}_{2}\hbox{O}_{3}$
deposition as measured by time-of-flight secondary ion mass spectroscopy, indicating indium as a possible origin of the oxide traps. The results suggest a new mechanism for the sulfur action at the InGaAs surface, which might be responsible for the transistor performance improvements observed after
$( \hbox{NH}_{4})_{2}\hbox{S}$
passivation. This mechanism involves sulfur as an indium diffusion/segregation barrier stabilizing the InGaAs surface during the ALD
$ \hbox{Al}_{2}\hbox{O}_{3}$
deposition, lowering the oxide trap density. This, in turn, improves the electron mobility through a reduction in the Coulomb scattering of the carriers due to border traps and improves the device drive current.