Issei Watanabe

547-GHz f/sub t/ In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As HEMTs with reduced source and drain resistance

We fabricated 30-nm gate pseudomorphic channel In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n/sup +/-InGaAs and n/sup +/-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g/sub m/) reached 1.5 S/mm, and the off-state breakdown voltage (BV/sub gd/) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f/sub t/) of 547 GHz and a simultaneous maximum oscillation frequency (f/sub max/) of 400 GHz were achieved: the best performance yet reported for any transistor.

Optimized channel thickness for high electron mobility in pseudomorphic In0.74Ga0.26As/In0.52Al0.48As quantum-well HEMT structures with (411)A super-flat interfaces grown by MBE

We have investigated channel thickness (L w ) dependence of transport properties of two-dimensional-electron gas (2DEG) in pseudomorphic In 0.74 Ga 0.26 As/In 0.52 Al 0.48 As quantum well high electron mobility transistor (QW-HEMT) structures with extremely flat heterointerfaces [(411)A super-flat interfaces] grown on (411)A InP substrates by molecular beam epitaxy (MBE). The highest electron mobility of 90,500 cm 2 /Vs (77 K) with a sheet carrier concentration (N s ) of 3.1 × 10 12 cm - was observed for the (411)A QW-HEMT structure with L w = 8 nm. which is about 1.5 times larger than the best value (μ = 61.000 cm 2 /Vs at 77 K) of ever reported electron mobility with a similar N s of 3.0 x 10 12 cm 2 for the InGaAs/InAlAs QW-HEMT structure grown on a ( 100) InP substrate. This enhancement of the electron mobility of the (4 11)A QW-HEMT structure is mainly due to much improved flatness of the (411)A InGaAs InAlAs heterointerfaces compared with those of conventional (100) interfaces, which results in a large reduction of interface roughness scattering of 2DEG.

Low-Profile Terahertz Radar Based on Broadband Leaky-Wave Beam Steering

We demonstrate short-range terahertz radar based on a leaky-wave antenna with a beam steering capability. As a proof of concept, we develop a microstrip-based periodic leaky-wave antenna driven by a vector network analyzer. By sweeping the frequency from 235 to 325 GHz, beam steering from -23° to +15° across the broadside can be achieved with a nearly constant beam width of 4°. Small target detection is demonstrated by locating a metal cylinder with a diameter of 12 mm placed 46-86 mm in front of the antenna with a mean error of 2.4 mm. The use of a leaky-wave antenna can pave the way for developing a low-loss, low-profile, and wide-aperture terahertz radar. Importantly, it can be integrated with a solid-state source and a detector. The proposed approach is particularly promising for use with emerging small devices such as drones or wearable devices, where millimeter-wave radar is not suitable in terms of the resolution and system footprint.

Velocity Enhancement in Cryogenically Cooled InP-Based HEMTs on (411)A-Oriented Substrates

An extremely high maximum transconductance g_mmax of 2.25 S/mm and a cutoff frequency f_T of 310 GHz was achieved at a cryogenic temperature (16 K) in a 195-nm-gate In_0.75Ga _0.25As/In_0.52Al_0.48As high electron mobility transistor (HEMT) fabricated on a (411)A-oriented InP substrate by molecular beam epitaxy, compared with room temperature values (g_mmax=1.78 S/mm and f_T=245 GHz). These significantly enhanced g_mmax and f_T values are attributed to a high electron velocity of up to 4.9times10⁷ cm/s due to suppressing phonon scattering in the In_0.75Ga_0.25As/In_0.52Al_0.48As HEMT with (411) A super-flat InGaAs/InAlAs interfaces (effectively atomically flat heterointerfaces over a wafer-size area)

Nanogate InP-HEMT technology for ultrahigh-speed performance

We succeeded in fabricating decananometer-gate InGaAs/InAlAs high electron mobility transistors (HEMTs) with extremely high current gain cutoff frequencies (f/sub T/s) of up to 562 GHz. The superior high-speed performance was obtained through laterally scaling the gate length (L/sub g/) and the gate-recess length, introducing a double recessed cap structure, and vertically scaling the gate-channel distance. We investigated the effect of these structures on the high-frequency performance, and clarified their advantages for the ultrahigh-speed operation from the view point of enhanced electron overshoot velocity, reduced parasitic source and drain resistances, and suppressed short channel effect.

Characterization of interface roughness scattering of electrons in an In0.53Ga0.47As/In0.52Al0.48As QW-HEMT structure with (4 1 1)A super-flat interfaces

In order to characterize interface roughness scattering, two-dimensional electron gas (2DEG) mobility in (411)A and (100) selectively-doped In 0.53 Ga 0.47 As/In0 .52 Al 0.48 As quantum well (QW) HEMT structures, which were grown on InP substrates by molecular beam epitaxy, with a gate contact was measured at 20K as a function of sheet electron concentration (Ns) by changing gate bias. Thickness of the QW was designed to be rather small (6 nm) for enhancing the interface roughness scattering for both samples. 2 DEG mobilities of the (411)A sample were 21,000-51,400 cm 2 /Vs in the range of Ns = 0.7-1.7 x10 12 cm -2 , which are about more than 2 times higher than the mobilities (8,700-25, 400cm 2 / Vs) of the conventional (100) sample. 2DEG mobility was calculated by taking into account interface roughness scattering and ionized remote impurity scattering. By fitting the calculated results to the observed ones, lateral size (A) and height (A) of the interface roughness of the (411)A sample were determined to be 3.5 and 0.23 nm, respectively, which are 30% and 50% smaller than the corresponding values (Λ = 5.0 nm and Δ = 0.43 nm) of the (100) sample.

Mobility enhancement by reduced remote impurity scattering in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor structure with (411)A super-flat interfaces grown by molecular-beam epitaxy

We have carried out a Shubnikov–de Haas (SdH) measurement at 4 K and investigated the electronic properties and scattering mechanisms in a pseudomorphic In0.7Ga0.3As/In0.52Al0.48As quantum well high electron mobility transistor (QW-HEMT) structure with a thin spacer thickness of 3 nm grown on a (411)A-oriented InP substrate by molecular-beam epitaxy (MBE). Electrons occupied the zeroth and first subbands in the 12-nm-thick In0.7Ga0.3As channel layer at two-dimensional electron gas (2DEG) densities of 3.10×1012 and 0.99×1012 cm−2, respectively. 2DEG mobilities of the (411)A sample for the zeroth and first subbands were μ0=52 000 and μ1=66 000 cm2/V s, which were much higher than those of the (100) QW-HEMT structure (μ0=22 000 and μ1=26 000 cm2/V s). The result indicates that the electron mobility of the (411)A sample is enhanced by reduction of remote impurity scattering because the spacer thickness (Lsp=3 nm) and distribution of sheet doped impurities are laterally uniform in the (411)A In0.7Ga0.3As/In0.5...

Demonstration of 20-Gbps wireless data transmission at 300 GHz for KIOSK instant data downloading applications with InP MMICs

We present 20-Gbps wireless ASK data transmission at 300 GHz with an all-electronic transmitter and receiver for KIOSK instant data downloading applications. The transmitter and receiver MMICs are based on 70-nm indium-phosphide-based high electron mobility transistor technologies of which the cut-off frequency (fmax) is approximately 700 GHz. For an experiment, the transmitter and receiver were packaged in a split-block waveguide and dedicated metallic housing, respectively. With 30-dBi and 25-dBi horn antennas for the transmitter and receiver, error free data transmission (bit error rate <; 1 × 10-9) was achieved up to 80-cm link distance.

Effects of Heterointerface Flatness on Device Performance of InP-Based High Electron Mobility Transistor

We achieved a current gain cutoff frequency ( fT) of 310 GHz at a cryogenic temperature (16 K) in a 195-nm-long gate In0.75Ga0.25As/In0.52Al0.48As high-electron-mobility transistor (HEMT) fabricated on a (411)A-oriented InP substrate. This is 27% higher than that at room temperature (245 GHz). For a corresponding HEMT fabricated on a (100) InP substrate, fT of 268 GHz was also obtained at 16 K, which is 15% higher than that obtained at 300 K (233 GHz). For both (411)A and (100) HEMTs, this significant enhancement in low-temperature fTs was caused by the increased average electron velocity under the gate (vave), which was mainly due to the suppression of phonon scattering. Furthermore, fT as high as 310 GHz was attributed to vave of up to 4.9×107 cm/s at 16 K for the (411)A HEMTs. This is higher than that of the (100) HEMTs (4.5×107 cm/s) and is due to the reduced interface roughness scattering of electrons caused by (411)A super-flat InGaAs/InAlAs interfaces (effectively atomically flat heterointerfaces over a wafer-size area).

Ultra-High-Speed Low-Noise InP-HEMT Technology

InP-based high electron mobility transistors (InP-HEMTs) with an ultra-high current gain cutoff frequency (fT) of over 550 GHz and a maximum oscillation frequency (fmax) of 500 GHz are realized. The excellent performance is achieved through lateral and/or vertical device scaling in combination with a reduction of parasitic resistances and capacitances. Key device technologies for ultra-high-speed, low-noise performance are described