Electrical and material characterization of atomic-layer-deposited Al2O3 gate dielectric on ammonium sulfide treated GaAs substrates
Cheng, Chao-Ching; Chien, Chao-Hsin; Luo, Guang-Li; Chang, Ching-Chih; Kei, Chi-Chung; Yang, Chun-Hui; Hsiao, Chien-Nan; Perng, Tsong-Pyng; Chang, Chun-Yen
Taiwan

For more than four decades, the absence of thermodynamically stable insulators on III-V compound semiconductors, e.g., (In)GaAs and InSb, etc, have become the foremost bottleneck to III-V technology rivaling or exceeding the properties of Si MOSFETs. Numerous efforts have been devoted in intensively questing high quality, competitive gate dielectrics and efficient passivation methods on III-V materials, respectively. Except for SiO2and Si3N4, (Gd,Ga)2O3 and ALD Al2O3, HfO2 high-k dielectrics are of particular interest. Meanwhile, the sulfur chemical treatment as well as Si and Ge interfacial passivation layers are currently active approaches to protect the III-V surface prior to the dielectric film deposition. In this study, we in detail investigated the impact of the ammonium sulfide (NH4)2S immersion and post-deposition annealing on the electrical properties of Pt/ALD-Al2O3/GaAs MOS capacitors by examining the C-V, G-V and gate leakage characteristics, respectively. TEM, photoluminescence (PL) and XPS were employed to analyze the entire structure and the dielectric-substrate interface, respectively. It was found that the sulfidization passivation obviously improved the capacitor characteristics that higher oxide capacitance and reduced interface state density (Dit) with lower leakage current were observed. Subsequent postdeposition annealing (PDA) in N2 and O2 ambient, respectively, further diminished a large part of existed charge trapping sites; but, generated the additional surface states and increased gate leakage current as well. These phenomena are closely related to thermal stability of the Al2O3/GaAs interface and can be explained in combination with the physical characterizations. After performing the (NH4)2S pretreatment, we suppressed the formation of (Ga,As)Ox native oxide at interface; a higher PL emission intensity at the wavelength of ~870 nm, corresponding to the better interface quality. However, a small amount of the (Ga,As)Ox oxide still presented inside the overlying Al2O3 films after high-temperature PDA processing.
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