The surface leakage currents and the surface trapping effects of the AlGaN/GaN high electron mobility transistors (HEMTs) on silicon with different passivation schemes, namely, a 120 nm plasma enhanced chemical vapor deposited SiN, a 10 nm atomic layer deposited (ALD) ${\text{Al}}_2{\text{O}}_3$ and a bilayer of $\text{SiN}/{\text{Al}}_2{\text{O}}_3$ (120/10 nm) have been investigated. After SiN passivation, the surface leakage current of the GaN HEMT was found to increase by about six orders; while it only increased by three orders after the insertion of ${\text{Al}}_2{\text{O}}_3$ between SiN and AlGaN/GaN. The surface conduction mechanism is believed to be the two-dimensional variable range hopping for all the samples. The leakage current in the etched GaN buffer layer with $\text{SiN}/{\text{Al}}_2{\text{O}}_3$ bilayer passivation was also much smaller than that with only SiN passivation. The pulse measurement shows that the bilayer of $\text{SiN}/{\text{Al}}_2{\text{O}}_3$ passivation scheme can effectively reduce the surface states and suppress the trapping effects.

This Letter reports on the epitaxial growth, characterization, and device characteristics of crack-free AlGaN/GaN heterostructures on a 200 mm diameter Si(111) substrate. The total nitride stack thickness of the sample grown by the metal-organic chemical vapor deposition technique is about 3.3 ± 0.1 μm. The structural and optical properties of these layers are studied by cross-sectional scanning transmission electron microscopy, high-resolution x-ray diffraction, photoluminescence, and micro-Raman spectroscopy techniques. The top AlGaN/GaN heterointerfaces reveal the formation of a two-dimensional electron gas with average Hall mobility values in the range of 1800 to 1900 cm²/Vs across such 200 mm diameter GaN on Si(111) samples. The fabricated 1.5 μm-gate AlGaN/GaN high-electron-mobility transistors exhibited the drain current density of 660 mA/mm and extrinsic transconductance of 210 mS/mm. These experimental results show immense potential of 200-mm diameter GaN-on-silicon technology for electronic device applications.

The effects of ${\text{Al}}_2{\text{O}}_3$ gate insulator grown by atomic layer deposition (ALD) system on the two-dimensional electron gas (2DEG) transport characteristics in AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. The shape of the electron lateral distribution in the quantum well at AlGaN/GaN interface was found to be slightly influenced by the ${\text{Al}}_2{\text{O}}_3$ thin layer. The drift mobility $\left({\mu }_{\text{d}}\right)$ of the electrons in ALD-${\text{Al}}_2{\text{O}}_3/\text{AlGaN}/\text{GaN}$ MISHEMT is increased due to the surface passivation effects of the included dielectric layer. The higher dynamic channel current of the MISHEMT indicates that the electron saturation velocity $\left(v_{\text{sat}}\right)$ is also increased. These results show the improvement of the transport characteristics of 2DEG in ${\text{Al}}_2{\text{O}}_3/\text{AlGaN}/\text{GaN}$ MISHEMT by the excellent properties of the ${\text{Al}}_2{\text{O}}_3$ grown by ALD.

We report here 305 GHz f _T , 340 GHz f _max , and 1550 mS/mm extrinsic g/sub m/ from a 0.10 μm In/sub x/Ga/sub 1-x/As/In/sub 0.62/Al/sub 0.48/As/InP HEMT with x graded from 0.60 to 0.80. This device has the highest f _T yet reported for a 0.10 μm gate length and the highest combination of f _T and f _max reported for any three-terminal device. This performance is achieved by using a graded-channel design which simultaneously increases the effective indium composition of the channel while optimizing channel thickness.