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

Abstract

Trap spectroscopy by charge injection and sensing method was applied to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\hbox{In}_{0.53}\hbox{Ga}_{0.47}\hbox{As}{-}\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> system, yielding the spatial and energetic distribution of the traps inside the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$ </tex></formula> layer. The trap density inside the atomic-layer-deposited (ALD) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX"> $\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> layer was found to be significantly reduced by <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{NH}_{4})_{2}\hbox{S}$</tex></formula> treatment of the InGaAs surface prior to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> deposition. Indium concentration inside the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> layer was found to be reduced once the InGaAs surface is <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{NH}_{4})_{2}\hbox{S}$</tex> </formula> treated prior to the <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> 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 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$( \hbox{NH}_{4})_{2}\hbox{S}$</tex></formula> passivation. This mechanism involves sulfur as an indium diffusion/segregation barrier stabilizing the InGaAs surface during the ALD <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$ \hbox{Al}_{2}\hbox{O}_{3}$</tex></formula> 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.