Browsing by Author "Tseng, Chih-Kuo"

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Improved electrical properties of Gd2O3/GaAs capacitor with modified wet-chemical clean and sulfidization procedures
(2008)
Cheng, Chao-Ching
;
Chien, Chao-Hsin
;
Luo, Guang-Li
;
Tseng, Chih-Kuo
;
Chiang, Hsin-Che
In this study we demonstrated improved electrical characteristics of Gd2O3 dielectric thin films on n-GaAs substrate by manipulating wet-chemical clean and (NH4)(2)S passivation. With X-ray photoelectron spectroscopy analysis, the HCl-cleaned GaAs surface was characterized to possess oxide species mainly in the form of AS(2)O(x) near the outmost surface and Ga2Ox with elemental arsenic close to the interface. These undesirable components could be suppressed through rinsing in NH4OH alkaline solution and then performing sulfidization at 80 degrees C, resulting in alleviating the Fermi level pinning effect on Gd2O3/GaAs capacitor performance. Higher oxide capacitance and alleviated frequency dispersion at the accumulation/depletion regimes were achieved, accompanied by negligible charge trapping (< 100 mV). Accordingly, gate leakage J(g) was lowered to ca. 10(-5) A/cm(2) at gate voltage V-g = (V-FB + 1) V, which was comparable to the recently reported performance of HfO2/GaAs structure with an ultrathin Si/Ge interfacial layer. We attributed the electrical improvements to the enhanced stabilization of high-k/sulfur-terminated GaAs interface due to abatement of native oxides and excess arsenic segregation. (C) 2007 The Electrochemical Society.
Study of thermal stability of HfOxNy/Ge capacitors using postdeposition annealing and NH3 plasma pretreatment
(2007)
Cheng, Chao-Ching
;
Chien, Chao-Hsin
;
Luo, Guang-Li
;
Yang, Chun-Hui
;
Kuo, Mei-Ling
We studied the thermal stability of the as-deposited HfOxNy thin films on the Ge substrate by employing rapid thermal annealing. After undergoing high-temperature processing, we observed several interesting physical and electrical features presented in the HfOxNy/Ge system, including a large Ge out-diffusion (>15 atom %) into high-k films, positive shift of the flatband voltage, severe charge trapping, and increased leakage current. These phenomena are closely related to the existence of GeOx defective layer and the degree of resultant GeO volatilization. We abated these undesirable effects, especially for reducing the amount of Ge incorporation (< 5 atom %) and the substoichiometric oxide at dielectric-substrate interface, through performing NH3 plasma pretreatment on the Ge surface. These improvements can be interpreted in terms of a surface nitridation process that enhanced the thermal stability of the high-k/Ge interface. In addition, we measured that the conductance loss in inversion was still high and it revealed independence with respect to gate bias, reflecting the fact that the minority carriers in Ge can rapidly respond either through a diffusion mechanism or through midgap trap states residing in Ge bulk substrates. (C) 2007 The Electrochemical Society.