Yen-Chang Hsieh

High-speed GaAs metal gate semiconductor field effect transistor structure grown on a composite Ge∕GexSi1−x∕Si substrate

In this study we used a low-pressure metal organic vapor phase epitaxy method to investigate the growth of GaAs metal gate semiconductor field effect transistor (MESFET) structures on a Si substrate. The buffer layer between the Si substrate and the grown GaAs epitaxial layers was a composite Ge∕Si0.05Ge0.95∕Si0.1Ge0.9 metamorphic layer. We used transmission electron microscopy to observe the microstructures formed in the grown GaAs∕Ge∕SixGe1−x∕Si material and atomic force microscopy to analyze the surface morphology and the formation of antiphase domains in the GaAs epitaxial layers. The measured Hall electron mobility in the channel layer of a MESFET structure grown on a 6° misoriented Si substrate was 2015 cm2 V−1 s−1 with a carrier concentration of 5.0×1017 cm−3. The MESFET device fabricated on this sample exhibited good current-voltage characteristics.

Self-assembled In0.22Ga0.78As quantum dots grown on metamorphic GaAs/Ge/SixGe1-x/Si substrate

Self-assembled In0.22Ga0.78As quantum dots (QDs) grown on Si substrate with Ge∕SiGe as buffer layer grown by metal organic vapor phase epitaxy were investigated. Transmission electron microscopy and atomic force microscopy images were used to observe the size and space distribution of the In0.22Ga0.78As QDs grown on the GaAs∕Ge∕GeSi∕Si layer structure. The influence of the growth temperature on the QDs size and density distribution was investigated. For QDs grown at 450°C, the density of the In0.22Ga0.78As dots was estimated to be 1×1011cm−2 and the In0.22Ga0.78As QDs thickness was 5 ML (monolayer) thick.

Copper-Airbridged Low-Noise GaAs PHEMT With

A GaAs pseudomorphic HEMT (PHEMT) with Cu-metallized interconnects was successfully developed. Sputtered WN_x was used as the diffusion barrier and Ti was used as the adhesion layer to improve the adhesion between WN_x/Cu interface in the thin-metal structure. After copper metallization, the PHEMTs were passivated with silicon nitride to avoid copper oxidation. The Cu-airbridged PHEMT showed the saturation I_DS was 250 mA/mm and the g_m was 456 mS/mm. The Ti adhesion layer plays a significant role on the g _m and V_p uniformity of the Cu-metallized PHEMTs. The GaAs PHEMTs with Ti/WN_x/Ti/Cu multilayer have better noise figure and associated gain than those of the devices without the Ti adhesion layer. The fabricated Cu-metallized GaAs PHEMT with Ti/WN _x/Ti/Cu multilayer has a noise figure of 0.76 dB and an associated gain of 8.8 dB at 16 GHz. The cutoff frequency (f_T) is 70 GHz when biased at V_DS=1.5V. These results show that the Ti/WN_x/Ti multilayer can serve as a good diffusion barrier for Cu metallization process of airbridge interconnects on GaAs lownoise PHEMTs

hboxTi/hboxWN_x/hboxTi

Electrical characteristics and thermal stability of the Ti∕Pt∕Cu Schottky contact on InAlAs were investigated. The Ti∕Pt∕Cu Schottky contact had comparable electrical properties compared to the conventional Ti∕Pt∕Au contact after annealing. As judged from the material analysis, the Ti∕Pt∕Cu on InAlAs after 350°C annealing showed no diffusion sign into the InAlAs. After 400°C annealing, the interfacial mixing of Cu and the underlying layers occurred and resulted in the formation of Cu4Ti. The results show that Ti∕Pt∕Cu Schottky contact using platinum as the diffusion barrier is very stable up to 350°C annealing and can be used for InAlAs∕InGaAs high-electron mobility transistors and monolithic microwave integrated circuits.

Diffusion Barrier for High-Frequency Applications

Al0.12Ga0.88As/In0.18Ga0.82As high-electron-mobility transistor (HEMT) growth on a Si substrate using the Ge/GexSi1-x buffer is demonstrated. This is the first demonstration of Al0.12Ga0.88As/In0.18Ga0.82As HEMT growth on a Ge/GexSi1-x metamorphic buffer layer. The electron mobility in the In0.18Ga0.82As channel of the HEMT sample was 3,550 cm2/(Vs). After fabrication, the HEMT device demonstrated a saturation current of 150 mA/mm with a transconductance of 155 mS/mm. The well behaved characteristics of the HEMT device on the Si substrate are believed to be due to the very thin buffer layer achieved and the lack of the antiphase boundary (APB) formation and Ge diffusion into the GaAs layers.

Thermal stability of Ti∕Pt∕Cu Schottky contact on InAlAs layer

An AlGaAs/InGaAs HEMT grown on Si substrate with Ge/Ge x Si 1−x buffer is demonstrated. The Ge/Ge x Si 1−x metamorphic buffer layer used in this structure was only 1.0 μgm thick. The electron mobility in the In 0.18 Ga 0.82 As channel of the HEMT sample was 3,550 cm 2 /Vs. After fabrication, the HEMT device demonstrated a saturation current of 150 mA/mm and a maximum transconductance of 155 mS/mm. The well behaved characteristics of the HEMT device on the Si substrate are believed to be due to the very thin buffer layer achieved and the lack of the antiphase boundaries (APBs) formation and Ge diffusion into the GaAs layers.

AlGaAs/InGaAs High Electron Mobility Transistor Grown on Si Substrate with Ge/GexSi1-x Metamorphic Buffer Layers

Self-assembled In/sub 0.22/Ga/sub 0.78/As quantum dots (QDs) fabricated on Si substrate with Ge buffer by metal organic vapor phase epitaxy (MOVPE) were investigated. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) images were used to observe the size and distribution of the In/sub 0.22/Ga/sub 0.78/As QDs grown on the GaAs/Ge/GeSi/Si layer structure. The influence of the growth temperature on the QDs density and distribution was investigated. For QDs grown at 430 /spl deg/C, the density of the In/sub 0.22/Ga/sub 0.78/As dots was estimated to be 1/spl times/10/sup 11/ cm/sup -2/ and the In/sub 0.22/Ga/sub 0.78/As QDs thickness was 5 monolayer thick.