S. Vicknesh

AlGaN/GaN two-dimensional-electron gas heterostructures on 200 mm diameter Si(111)

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 devi...

Direct Current and Microwave Characteristics of Sub-micron AlGaN/GaN High-Electron-Mobility Transistors on 8-Inch Si(111) Substrate

We report for the first time the DC and microwave characteristics of sub-micron gate (~0.3 µm) AlGaN/GaN high-electron-mobility transistors (HEMTs) on 8-in. diameter Si(111) substrate. The fabricated sub-micron gate devices on crack-free AlGaN/GaN HEMT structures exhibited good pin.-off characteristics with a maximum drain current density of 853 mA/mm and a maximum extrinsic transconductance of 180 mS/mm. The device exhibited unit current-gain cut-off frequency of 28 GHz, maximum oscillation frequency of 64 GHz and OFF-state breakdown voltage of 60 V. This work demonstrates the feasibility of achieving good performance AlGaN/GaN HEMTs on 8-in. diameter Si(111) for low-cost high-frequency and high-power switching applications.

Demonstration of submicron-gate AlGaN/GaN high- electron-mobility transistors on silicon with complementary metal-oxide-semiconductor-compatible non-gold metal stack

We have demonstrated 0.15-µm-gate-length AlGaN/GaN high-electron-mobility transistors (HEMTs) with direct-current (DC) and microwave performances for the first time using a complementary metal–oxide–semiconductor (CMOS)-compatible non-gold metal stack. Si/Ta-based ohmic contact exhibited low contact resistance (Rc=0.24 Ωmm) with smooth surface morphology. The fabricated GaN HEMTs exhibited gmmax=250 mS/mm, fT/fmax=39/39 GHz, B Vgd=90 V, and drain current collapse <10%. The device Johnsons figure of merit (J-FOM = fT × B Vgd) is in the range between 3.51 to 3.83 THzV which are comparable to those of other reported GaN HEMTs on Si with a conventional III–V gold-based ohmic contact process. Our results demonstrate the feasibility of realizing high-performance submicron GaN-on-silicon HEMTs using a Si CMOS-compatible metal stack.

Improved Power Device Figure-of-Merit (4.0×108 V2 Ω-1 cm-2) in AlGaN/GaN High-Electron-Mobility Transistors on High-Resistivity 4-in. Si

The OFF-state breakdown voltage (BVgd) characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) on a 4-in. Si substrate were investigated and analyzed. The HEMTs with Lgd = 10 µm exhibited BVgd of 723 V with the specific on-resistance RDS[ON] of 1.3 mΩ cm2. Due to the improved ohmic contact, the devices exhibited low RDS[ON] values. The power device figure-of-merit (FOM=BVgd2/RDS[ON]) is as high as 4.0×108 V2 Ω-1 cm-2, the highest among the reported values for GaN HEMTs on a 4-in. Si. Due to the low vertical buffer leakage current, a high vertical breakdown voltage of ~1200 V has been achieved with the total buffer thickness (dBuff) of 2.2 µm.

Enhanced Breakdown Voltage With High Johnson's Figure-of-Merit in 0.3-

Enhanced OFF -state breakdown voltage has been observed in ammonium sulfide [(NH₄)₂S_x]-treated AlGaN/GaN high electron mobility transistors (HEMTs) on Si substrate without compromising the unit gain cutoff frequencies. About six times higher OFF -state breakdown voltage (BV_gd) and three orders of magnitude higher I_ON/I_OFF ratio were observed in the (NH₄)₂S_x-treated 0.3- μm T-gate conventional AlGaN/GaN HEMTs on Si substrate. In addition, three orders of magnitude lower surface leakage current (~3.0 μA/mm to ~3 nA/mm) have also been observed on the (NH₄)₂S_x-treated devices. The calculated Johnsons figures of merit (J-FOM = BV_gd × f_T) is 5.41 × 10¹² V/s, which is the highest value reported so far for 0.3- μm T-gate conventional SiN passivated AlGaN/GaN HEMTs without the incorporation of field plate. No significant drain current collapse was observed on the (NH₄)₂S_x-treated devices.

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We report for the first time high-frequency microwave noise performance on 0.17-μm T-gate In_0.17Al_0.83N/GaN high-electron mobility transistors (HEMTs) fabricated on Si(111). The HEMTs exhibited a maximum drain current density of 1320 mA/mm, a maximum extrinsic transconductance of 363 mS/mm, an unity current gain cutoff frequency (f_T) of 64 GHz and, a maximum oscillation frequency [fmax ^(U)/ f_max (MSG)] of 72/106 GHz. The product f_max(U) × L_g=12.24 GHz· μm is the highest value ever reported for InAlN/GaN HEMTs on Si substrate. At V_d=4 V and V_g=-2.25 V, the device exhibited a minimum noise figure (NF_min) of 1.16 dB for 10 GHz and 1.76 dB for 18 GHz. Small variation of NF_min (<;0.5 dB) from 8% to 48% with I_Dmax (100-636 mA/mm) was observed.

T-gate AlGaN/GaN HEMTs on Silicon by

In this study, the authors have employed micro-Raman scattering to characterize the residual stress in freestanding GaN-based micromechanical structures on (111)-oriented silicon substrates. Arrays of freestanding cantilevers and microbridges have been fabricated using a combination of dry etching techniques. The Si material beneath the GaN microstructures is removed by a nonplasma XeF2-based dry release technique. Two distinct sets of GaN-based layers on Si(111) with a different amount of growth-induced tensile stress are selected for the fabrication of freestanding cantilevers. The residual stress in these micromechanical structures is determined from the peak shift of the E2-high phonon mode of GaN. Such GaN mechanical structures on Si platforms may be useful for the fabrication of GaN-based microelectromechanical systems and sensors.

({\rm NH}_{4})_{2}{\rm S}_{x}

The authors demonstrate the use of a dry releasing technique to achieve deeply undercut GaN-based microdisk structures supported by silicon platforms. Varying dimensions of microdisk structures on silicon posts with large air gaps are fabricated by a XeF2-based dry etching of the underlying silicon material. The residual stress variation in these microdisks is studied by high spectral resolution micro-Raman mapping. Such a fabrication technique may effectively improve the light extraction efficiency from GaN-based microdisk light emitting diodes on silicon substrates.

Treatment

In this study, the authors report on the fabrication processes to realize the freestanding ZnO micromechanical structures on Si(111) substrates. Arrays of freestanding cantilevers and microbridges have been fabricated using a combination of dry etching techniques. The mechanical properties of the released ZnO structures are characterized by micro-Raman spectroscopy. The residual stress in these freestanding micromechanical structures is determined from the E2(2) phonon peak shift. Such a method to realize the freestanding structures on Si platform would be useful for the fabrication of ZnO-based microelectromechanical systems and sensors.

High-Frequency Microwave Noise Characteristics of InAlN/GaN High-Electron Mobility Transistors on Si (111) Substrate

High performance undoped AlGaN/AlN/GaN high electron mobility transistors (HEMTs) on high resistivity Si were achieved by implementing an ohmic-recess contact by inductively coupled plasma etching using four layers of Ti/Al/Ni/Au metal. About a 17.5% increase in drain current density and a 12.5% increase in extrinsic transconductance were observed on ohmic-recess-etched HEMTs. This is due to the reduction in the parasitic resistance such as contact resistance, drain resistance, and source resistance of the device. The ohmic-recess-etched AlGaN/AlN/GaN HEMT with a 6.0 μm gate-drain spacing exhibited the lowest specific on-resistance (R DS(ON) ) of 0.22 mΩ cm 2 with an off-state breakdown voltage (BV GD ) of 194 V. The highest ever reported figure-of-merit BV 2 CD /R DS(ON) = 1.79 × 10 8 V 2 Ω -1 cm -2 has been achieved in the ohmic-recess-etched AlGaN/AlN/GaN HEMTs on silicon. Ohmic recess is useful for undoped AlGaN/AlN/GaN HEMTs to achieve low R DS(ON) with high figure-of-merit.