Patrick Fay

InAlN/AlN/GaN HEMTs With Regrown Ohmic Contacts and

We report 30-nm-gate-length InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs) with a record current gain cutoff frequency (fT) of 370 GHz. The HEMT without back barrier exhibits an extrinsic transconductance (gm.ext) of 650 mS/mm and an on/off current ratio of 106 owing to the incorporation of dielectric-free passivation and regrown ohmic contacts with a contact resistance of 0.16 Ω·mm. Delay analysis suggests that the high fT is a result of low gate-drain parasitics associated with the rectangular gate. Although it appears possible to reach 500-GHz fT by further reducing the gate length, it is imperative to investigate alternative structures that offer higher mobility/velocity while keeping the best possible electrostatic control in ultrascaled geometry.

f_{T}

This letter reports lattice-matched In_0.17Al_0.83N/GaN high-electron-mobility transistors on a SiC substrate with a record current gain cutoff frequency (f_T) of 300 GHz. To suppress the short-channel effects (SCEs), an In0.15Ga_0.85N back barrier is applied in an InAlN/GaN heterostructure for the first time. The GaN channel thickness is also scaled to 26 nm, which allows a good immunity to SCEs for gate lengths down to 70 nm even with a relatively thick top barrier (9.4-10.4 nm). In a 30-nm-gate-length device with an on-resistance (R_on) of 1.2 Ω · mm and an extrinsic transconductance (g_m.ext) of 530 mS/mm, a peak fa of 300 GHz is achieved. An electron velocity of 1.37-1.45 × 10⁷ cm/s is extracted by two different delay analysis methods.

of 370 GHz

High-electron mobility transistors (HEMTs) based on ultrathin AIN/GaN heterostructures with a 3.5-nm AlN barrier and a 3-nm Al₂O₃ gate dielectric have been investigated. Owing to the optimized AIN/GaN interface, very high carrier mobility (~1400 cm²/V ldr s) and high 2-D electron-gas density (~2.7times10¹³/cm²) resulted in a record low sheet resistance (~165 Omega/sq). The resultant HEMTs showed a maximum dc output current density of ~2.3 A/mm and a peak extrinsic transconductance g_m,ext~480 mS/mm (corresponding to g_m,int~1 S/mm). An f_T/f_max of 52/60 GHz was measured on 0.25times60 mum² gate HEMTs. With further improvements of the ohmic contacts, the gate dielectric, and the lowering of the buffer leakage, the presented results suggest that, by using AIN/GaN heterojunctions, it may be possible to push the performance of nitride HEMTs to current, power, and speed levels that are currently unachievable in AlGaN/GaN technology.

300-GHz InAlN/GaN HEMTs With InGaN Back Barrier

We report lattice-matched In_0.17Al_0.83N/GaN high-electron mobility transistors on a SiC substrate with a record current gain cutoff frequency (<i>fT</i>). The key to this performance is the use of an oxygen plasma treatment to form a thin oxide layer on the InAlN barrier and to reduce the gate leakage current by more than two orders of magnitude. In addition, the RF transconductance (<i>g</i>_m) collapse is reduced in the O₂-treated devices, which results in a significant improvement in the <i>f</i>_T . In a transistor with a gate length of 30 nm, an <i>f</i>_T of 245 GHz is achieved, the highest value ever reported in GaN-based field-effect transistors.

AlN/GaN Insulated-Gate HEMTs With 2.3 A/mm Output Current and 480 mS/mm Transconductance

Record high on-current of 78 μA/ μm in a tunnel field-effect transistor (TFET) is achieved at 0.5 V at room temperature. The TFET employs a staggered AlGaSb/InAs heterojunction with the tunneling direction oriented in-line with the gate field. The measured results are consistent with numerical simulation of the device structure. Simulations of optimized structures suggest that switching speed comparable to that of the MOSFET should be achievable with improvements in the source and drain resistances.

245-GHz InAlN/GaN HEMTs With Oxygen Plasma Treatment

The current-voltage characteristics of AlGaSb/InAs staggered-gap n-channel tunnel field-effect transistors are simulated in a geometry in which the gate electric field is oriented to be in the same direction as the tunnel junction internal field. It is shown that this geometry can also support low-voltage operation and low subthreshold swing. In the absence of a simple analytic theory for this transistor to allow direct analytic comparisons, two-dimensional numerical simulations are used to explore the electrostatic and geometrical design considerations including dependence on gate length, gate underlap, gate undercut, and equivalent oxide thickness.

AlGaSb/InAs Tunnel Field-Effect Transistor With On-Current of 78

This work focuses on dipole antenna-coupled metal-oxide-metal diodes, which can be used for the detection of long wave infrared radiation. These detectors are defined using electron beam lithography and fabricated with shadow evaporation metal deposition. Along with offering complementary metal oxide semiconductor compatible fabrication, these detectors promise high speed and frequency selective detection without biasing, a small pixel footprint, and full functionality at room temperature without cooling. Direct current current-voltage characteristics are presented along with detector response to 10.6μm radiation. The detection characteristics can be tailored to provide for multispectral imaging in specific applications by modifying device geometries.

\mu\hbox{A}/\mu\hbox{m}

Having a drain current density of 1.9 A/mm, a peak extrinsic transconductance of 800 mS/mm (the highest reported in III-nitride transistors), ft/fmax of 70/105 GHz, and Vbr of 29 V, 150-nm-gate enhancement-mode InAlN/AlN/GaN high-electron-mobility transistors are demonstrated on SiC substrates using plasma-based gate-recess etch. The possible plasma-induced damage in the gate region was investigated using interface-trap states extracted from temperature-dependent subthreshold slopes.

at 0.5 V

InAs/AlSb/AlGaSb heterojunction backward diodes are promising detectors for millimeter-wave imaging applications due to their high sensitivity, low noise, and high cutoff frequency. By using a device heterostructure with a thin (11 Å) barrier layer, δ-doped cathode, and optimized Al_xGa_1-xSb anode composition (x=12%), in conjunction with submicron (0.4×0.4 μm²) active area, fabricated detectors have demonstrated DC curvatures of -47 V^-1 and record unmatched sensitivities of 4600 V/W at 94 GHz. Impedance-matched sensitivities of 49,700 V/W at 94 GHz are projected from on-wafer S-parameter and sensitivity measurements. These detectors have measured junction resistances of 814 Ω·μm² and capacitances of 15 fF/μm². A record low NEP_min of 0.18 pW/Hz^1/2 has been projected under conjugate matching conditions. This study demonstrates the potential of Sb-heterostructure backward diodes as ultra-low-noise millimeter-wave direct detectors.

Performance of AlGaSb/InAs TFETs With Gate Electric Field and Tunneling Direction Aligned

InAs/AlSb/GaSb backward diodes are used for millimeter-wave square-law power detection. A new heterostructure design with low capacitance, low resistance, and high curvature coefficient as compared to previous designs is presented. Voltage sensitivity, which is directly proportional to curvature coefficient, is improved by 31% as compared to prior reports of devices with similar barrier thicknesses. The junction capacitance is also reduced by 24% to 13 . The improved sensitivity and decreased junction capacitance originate from the incorporation of a p-type-doping plane with sheet concentration of in the n-InAs cathode layer. The combination of low resistance (and thus Johnson noise) and high sensitivity results in an estimated noise equivalent power of 0.24 at 94 GHz for a conjugately matched source, whereas the reduced capacitance facilitates wideband matching and increases the detector cutoff frequency. These modified Sb-based detectors have promise for improving the performance of passive millimeter-wave and submillimeter-wave imaging systems.