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A stress engineered three dimensional (3D) Triple T-gate (TT-gate) on lattice matched In0.17Al0.83N/GaN nano-channel (NC) Fin-High-Electron-Mobility Transistor (Fin-HEMT) with significantly enhanced device performance was achieved that is promising for high-speed device applications. The Fin-HEMT with 200-nm effective fin-width (Weff) exhibited a very high IDmax of 3940 mA/mm and a highest gm of 1417 mS/mm. This dramatic increase of ID and gm in the 3D TTgate In0.17Al0.83N/GaN NC Fin-HEMT translated to an extracted highest electron velocity (ve) of 6.0 x 107cm/s, which is ~1.89 x higher than that of the conventional In0.17Al0.83N/GaN HEMT (3.17 x 107cm/s). The ve in the conventional III-nitride transistors are typically limited by highly efficient optical-phonon emission. However, the unusually high ve at 300 K in the 3D TT-gate In0.17Al0.83N/GaN NC Fin-HEMT is attributed to the increase of in-plane tensile stress component by SiN passivation in the formed NC which is also verified by micro-photoluminescence (0.47 ° 0.02 GPa) and micro-Raman spectroscopy (0.39 ° 0.12 GPa) measurements. The ability to reach the ve = 6 x 107cm/s at 300 K by a stress engineered 3D TT-gate lattice-matched In0.17Al0.83N/GaN NC Fin-HEMTs shows they are promising for next-generation ultra-scaled highspeed device applications. [ABSTRACT FROM AUTHOR]

The mechanisms of the temperature-dependent forward gate current transport in the atomic-layer-deposited Al2O3/AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) were investigated. In contrast to the conventional Schottky-gate AlGaN/GaN HEMT, thermionic field emission was found not to be the dominant transport mechanism for the Al2O3/AlGaN/GaN MISHEMT. Fowler-Nordheim tunneling was found to be dominant at low temperature (T<0 °C) and high electrical filed, whereas trap assistant tunneling was found to be dominant at medium electrical field and high temperature (T>0 °C). [ABSTRACT FROM AUTHOR]

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) Al2O3 and a bilayer of SiN/Al2O3 (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 Al2O3 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 SiN/Al2O3 bilayer passivation was also much smaller than that with only SiN passivation. The pulse measurement shows that the bilayer of SiN/Al2O3 passivation scheme can effectively reduce the surface states and suppress the trapping effects. [ABSTRACT FROM AUTHOR]

The effects of Al2O3 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 Al2O3 thin layer. The drift mobility (μd) of the electrons in ALD-Al2O3/AlGaN/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 (vsat) is also increased. These results show the improvement of the transport characteristics of 2DEG in Al2O3/AlGaN/GaN MISHEMT by the excellent properties of the Al2O3 grown by ALD. [ABSTRACT FROM AUTHOR]

The temperature dependent characteristics of Ti/Al/Ni/Au Ohmic contact for AlGaN/GaN high electron mobility transistors (HEMTs) on high-resistivity Si and sapphire substrates were investigated over the temperature range from -50 to 200 °C. The sheet resistances (Rsh) of AlGaN/GaN HEMTs on Si and sapphire substrates were found to increase with the temperature according to the power-law equation with power indices of -2.7 and -2.3, respectively. The specific contact resistivity (ρC) decreased with the temperature, and it was observed to be determined by the electron thermionic field emission (TFE) from the lowered conduction band edge in the modified AlGaN region with high-density N-vacancies to the quantum well at the AlGaN/GaN heterojunction with two dimensional electron gas (2DEG). Three important parameters in the TFE are extracted, that is, the barrier height ([lowercase_phi_synonym]B) of around 0.5 eV, the energy difference between the effective conductive-band edge and the Fermi level in 2DEG (En) of around 0.1 eV, and the 2DEG electron density (ND) with the order of magnitude of 1019 cm-3. [ABSTRACT FROM AUTHOR]

The AlGaN/GaN heterostructures (HSs) with high two dimensional electron gas mobility (1070 cm2/V s) were grown on nonpolar a-plane (1120) sapphire substrate by metal organic chemical vapor deposition. High crystalline quality (reduced screw, edge, and mixed dislocations) with small root mean square surface roughness and small peak-valley distance values were observed in a-plane sapphire grown AlGaN/GaN HSs. Hexagonal-GaN phase was also observed on a-plane sapphire grown AlGaN/GaN HSs. An average increase of ns up to 22% for a plane and 26% for c plane were found after Si3N4 passivation. The product of ns and μH also increases for both a-plane (19%) and c-plane (28%) sapphire grown AlGaN/GaN HSs in a wide range of measurement temperature (87–400 K). The enhancement of sheet carrier density by Si3N4 passivation for nonpolar (1120) sapphire grown AlGaN/GaN HSs is a useful result for the design of future GaN high-electron-mobility transistors. [ABSTRACT FROM AUTHOR]

The effects of gate-source (GS) and gate-drain (GD) region passivation on the drain current (ID) collapse in AlGaN/GaN high-electron-mobility transistors (HEMTs) were studied. Electrical stresses were applied to the GS and GD regions of HEMTs, (1) unpassivated (device A), (2) fully passivated (device B), (3) GD passivated only (device C), and (4) device C with additional full passivation (device D). An increase of ID density and the extrinsic transconductance was observed in devices with full Si3N4 passivation. Due to the increase of gate leakage current by Si3N4 passivation, breakdown voltage decreases. Device A exhibited severe (96%) ID collapse when it was electrically stressed in both the GS and GD regions. Devices C and D have suppressed only 14% of ID collapse after passivation. However, HEMTs with full Si3N4 passivation (device B) have suppressed more than 80% of the ID collapse. Full passivation is required to suppress the ID collapse effectively for AlGaN/GaN HEMTs. The remaining ID collapse (19%) of device B is affected primarily by bulk/buffer related traps rather than surface related traps. [ABSTRACT FROM AUTHOR]

A study of the properties of In0.52Al0.48As/In0.53+xGa0.47-xAs high electron mobility transistors is carried out for 0%, 7%, and 12% excess In values in the channel. Theoretical analysis shows that the enhanced In causes a biaxial compressive strain of 0.49% to 0.84% in the channel, increases the band-edge discontinuity from 0.437 to 0.500 eV, and reduces the carrier mass by 6%. Experimental characterizations support the theoretical predictions by demonstrating an increase of mobility from 9900 to 11 200 cm2/V s at 300 K, and a transconductance enhancement from 160 to at least 230 mS/mm. [ABSTRACT FROM AUTHOR]