Shiping Guo

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.

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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

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.

300-GHz InAlN/GaN HEMTs With InGaN Back Barrier

This letter studies the effect of AlGaN back barriers in the dc and RF performance of In0.17Al0.83N/GaN high-electron mobility transistors grown on SiC substrates. When compared to conventional structures without a back barrier, the back barrier effectively prevents the degradation of drain-induced barrier lowering and significantly improves the output resistance in sub-100-nm-gate-length devices. The reduction in short-channel effects helps to increase the frequency performance of AlGaN back-barrier devices. For a 65-nm gate length, the current gain cutoff frequency (fT) of a transistor with an AlGaN back barrier is 210 GHz, which is higher than that of the standard device with the same gate length (fT = 195 GHz).

245-GHz InAlN/GaN HEMTs With Oxygen Plasma Treatment

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.

InAlN/GaN HEMTs With AlGaN Back Barriers

We report the first CW Ka-band radio-frequency (RF) power measurements at 35 GHz from a passivated Al_0.82In_0.18N/GaN high-electron mobility transistor on SiC with 9.8-nm-thin barrier. This device delivered a maximum of 5.8 W/mm with a power-added efficiency of 43.6% biased at V_DS = 20 V and 10% I_DSS when matched for power at CW. The device was grown by metal-organic chemical vapor deposition with 2.8-¿m source-drain spacing and a gate length of 160 nm. An excellent ohmic contact was obtained with an R_c of 0.62 ¿·mm. The maximum extrinsic transconductance was 354 mS/mm with an I_DSS of 1197 mA/mm at a V_GS of 0 V, an ft of 79 GHz, and an f_max of 113.8 GHz.

Gate-Recessed Enhancement-Mode InAlN/AlN/GaN HEMTs With 1.9-A/mm Drain Current Density and 800-mS/mm Transconductance

We studied submicrometer (L_G = 0.15-0.25 ¿m) gate-recessed InAlN/AlN/GaN high-electron mobility transistors (HEMTs) on SiC substrates with 25-nm Al₂O₃ passivation. The combination of a low-damage gate-recess technology and the low sheet resistance of the InAlN/AlN/GaN structure resulted in HEMTs with a maximum dc output current density of I_DS,max = 1.5 A/mm and a record peak extrinsic transconductance of g_m,ext = 675 mS/mm. The thin Al₂O₃ passivation improved the sheet resistance and the transconductance of these devices by 15% and 25%, respectively, at the same time that it effectively suppressed current collapse.

High-Power Ka-Band Performance of AlInN/GaN HEMT With 9.8-nm-Thin Barrier

Nonalloyed ohmic contacts regrown by molecular beam epitaxy were made on InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs). Transmission-line-method measurements were carried out from 4 K to 350 K. Although the total contact resistance is dominated by the metal/ n+-GaN resistance ( ~ 0.16 Ω·mm), the resistance induced by the interface between the regrown n+ GaN and HEMT channel is found to be 0.05-0.075 Ω·mm over the entire temperature window, indicating a minimal barrier for electron flow at the as-regrown interface. The quantum contact resistance theory suggests that the interface resistance can be further reduced to be <; 0.02 Ω·mm in GaN HEMTs.

Gate-Recessed InAlN/GaN HEMTs on SiC Substrate With

We report 1000-transistor-level monolithic circuit integration of sub-30-nm gate-recessed E/D GaN high-electron-mobility transistors with <i>fT</i> and <i>f</i>_max above 300 GHz. Simultaneous <i>fT</i>/<i>f</i>_max of 348/340 and 302/301 GHz for E- and D-mode devices, respectively, was measured, representing a 58% increase in <i>fT</i> compared with our previous report, due to improved management of RC parasitic delay. Three-terminal E- and D-mode breakdown voltage of 10.7 and 11.8 V, respectively, is limited by gate-drain breakdown.

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This letter reports the fabrication of InAlN/GaN high-electron mobility transistors (HEMTs) with a three-terminal off-state breakdown voltage (BV) of 3000 V and a low specific on-resistance of 4.25 mΩ·cm². To reduce the drain-to-source leakage current in these devices, an AlGaN back barrier has been used. The gate leakage current in these devices is in the ~10^-10 A/mm range owing to the use of a SiO₂ gate dielectric. This current level is more than six orders of magnitude lower than in Schottky-barrier HEMTs. The combination of an AlGaN back barrier, the high charge sheet density of InAlN/GaN HEMTs, and the low leakage due to the gate-dielectric layer allows for a figure-of-merit BV²/<i>R</i>_ON,SP of ~2.1 × 10⁹ V²·Ω^-1·cm^-2.