Hiroki Sugiyama

Low‐temperature metal‐organic vapor‐phase epitaxy growth of strained InGaAs channel in InP‐based high electron mobility transistors (HEMTs) is investigated using trimethylindium, triethylgallium, and arsine as precursors. Lowering the growth temperature is crucial for suppressing lattice relaxation and increasing the channel In content up to 0.9. To control the composition of In‐rich InGaAs, the nonlinear relationship between the solid and vapor composition should be taken into account. We successfully fabricate InP HEMT structures with an In _0.9 Ga _0.1 As channel where electron mobility of around 14,000 cm ² V ⁻¹ s ⁻¹ at a sheet‐carrier concentration of around 2.5 × 10 ¹² cm ⁻² is obtained.

The impact of back-end-of-line (BEOL) processing on the performance of 60 nm InP-based high electron mobility transistors (HEMTs) was investigated. After BEOL processing, a prominent kink was observed in the I _d – V _ds characteristics of some HEMTs, which correlated with the deterioration in the 3 nm thick InP recess-etching stopper around the gate regions. Prolonged electrochemical recess etching likely promoted the oxidation and thinning of the stopper, diminishing the surface-passivation effect. This damaged stopper made the HEMTs susceptible to BEOL processing, resulting in the degradation in the I _d – V _ds characteristics. To suppress this degradation, reducing the recess-etching time (or recess length) was effective in maintaining the drain current and V _th . This made the HEMTs robust against BEOL processing, resulting in kink-free I _d – V _ds curves and better f _t and f _max (281.5 and 387.0 GHz, respectively) at a V _gs = −0.1 V and V _ds = 1.1 V after monolithic microwave integrated circuit fabrication.

We demonstrated the crystal growth of group-III arsenides (III-As) on GaN via an arsenidation layer and GaN-channel electron mobility transistors (HEMTs) with a regrowth InAs/GaAs source and drain (S/D) region. By annealing under an AsH3 atmosphere, the surface of a GaN (0001) template is arsenided. We grew ⟨111⟩ oriented InAs and GaAs on arsenided GaN. Silicon-doped n-type InAs with a carrier mobility of over 1500 cm2/V s and a carrier concentration of over 1 × 1019 cm−3 was successfully obtained. The fabrication process and direct-current characteristics of GaN-channel HEMTs with the regrown Si-doped InAs/GaAs S/D region were demonstrated for the first time. A maximum transconductance estimated from transfer characteristics was as high as ∼195 mS/mm for the HEMT with a gate length of 2 μm without passivation, which is comparable to those for the HEMT without any S/D regrowth. The impact of the InAs/GaAs S/D region on the on-resistance of the fabricated HEMTs was estimated to be ∼0.9 Ω mm, which can be reduced by optimizing the device structures and process conditions. These results indicate that the process of GaN arsenidation and III-As regrowth can be used without any device performance degradation. Therefore, further lowering the ohmic contact resistivity and on-resistance of GaN-channel HEMTs is possible by maturing the manufacturing-process technology of III-As-contained GaN-channel HEMTs.

2023 International Conference on Solid State Devices and Materials ,Feasibility Study of InP-based Tera-Hertz-ICs Fabrication Process for Beyond 5G / 6G Wireless Network Systems

Herein, we present a detailed analysis of the effects of O2 plasma treatment on the AlGaN barrier volume trap states in an Al0.45Ga0.45N/GaN high-electron mobility transistor. Compared to that of the as-grown sample, the single short-pulse ${I}_{D}$ – ${V}_{\text {GS}}$ characterization of the plasma-treated sample exhibited lower charge trapping inside the AlGaN barrier. The 1/ ${f}$ low-frequency noise characterization revealed a significant reduction of approximately 67% in the volume trap density of the AlGaN barrier layer after O2 plasma treatment. This was achieved by the formation of Al–O and Ga–O bonds via the penetration of oxygen ions into the AlGaN bulk, which resulted in reduced trap state density in the AlGaN barrier. In addition, the Schottky characteristics were improved notably. Consequently, the O2 plasma-treated sample did not display current collapse and showed steady drain current output under the reverse-sweep drain-stress bias conditions. Furthermore, the plasma treatment significantly reduced the RF transconductance ( ${g}_{m}$ ) collapse in the as-grown sample, and significantly increased the ${f}_{T}/{f}_{\text {max}}$ of the plasma-treated sample from 65/70 to 120/230 GHz for ${L}_{g}$ = 80 nm devices, respectively. Last, the O2 plasma-treated sample showed substantial improvements in ${P}_{\text {out}\_\max}$ , power added efficiency (PAE), and linear gain from 1.25 W/mm, 20%, and 15 dB to 2.4 W/mm, 50%, and 19 dB, respectively.

In this work, we fabricate directly modulated membrane distributed reflector (DR) lasers on a Si waveguide by utilizing micro-transfer printing method. Micro-transfer printing enables low-loss coupling between the lasers and the silicon photonics circuit, and since it is a back-end process, we can test the lasers prior to integration. A membrane laser is as thick as the Si waveguides, which makes optical coupling between the two quite easy. In addition, membrane lasers with a lateral p-i-n diode structure have low capacitance and a large optical confinement factor, which means they can achieve a low threshold current and high-speed modulation operation with low energy consumption. The fabricated membrane DR laser integrated with a 220-nm-thick Si waveguide exhibits a low threshold current of 1.2 mA and single-mode operation at 1535 nm with a side-mode suppression ratio (SMSR) of about 40 dB at the bias current of 14 mA. It also achieves the E-O bandwidth of over 25 GHz and 50-Gbit/s non-return-to-zero (NRZ) signal modulation with an extinction ratio of 2.5 dB.

We present a fully analytical model and physical investigation on the source resistance (R_S) in In_xGa_1−xAs quantum-well high-electron mobility transistors based on a three-layer TLM system. The R_S model in this work was derived by solving the coupled quadratic differential equations for each current component with appropriate boundary conditions, requiring only six physical and geometrical parameters, including ohmic contact resistivity (ρ_c), barrier tunneling resistivity (ρ_barrier), sheet resistances of the cap and channel regions (R_{sh_cap} and R_{sh_ch}), side-recessed length (L_side) and gate-to-source length (L_gs). To extract each model parameter, we fabricated two different TLM structures, such as cap-TLM and recessed-TLM. The developed R_S model in this work was in excellent agreement with the R_S values measured from the two TLM devices and previously reported short-L_g HEMT devices. The findings in this work revealed that barrier tunneling resistivity already played a critical role in reducing the value of R_S in state-of-the-art HEMTs. Unless the barrier tunneling resistivity is reduced considerably, innovative engineering on the ohmic contact characteristics and gate-to-source spacing would only marginally improve the device performance.

In this study, we investigated the impact of intrinsic output conductance (g_oi) on the short-circuit current-gain cut-off frequency (f_T) in In_xGa_1-xAs/In_0.52Al_0.48As quantum-well (QW) high-electron-mobility transistors. At its core, we attempted to extract values of f_T using a simplified small-signal model (SSM) of the HEMTs and to derive an analytical formula for f_T in terms of extrinsic model parameters that are related with intrinsic model parameters of a general SSM. We projected how f_T was influenced by g_oi in HEMTs, emphasizing that the improvement in electrostatic integrity would also be of critical importance to fully benefit from scaling down L_g.

Conventional techniques to characterize the carrier transport properties in high-electron-mobility transistors do not account for the effect of each individual unit process and device integration, and can be challenging to use for short-channel devices. To overcome this, we have developed a new technique that consists of measurement and analysis of the transconductance scaling behavior. The proposed ${g}_{m}$ modeling technique yielded the effective mobility, $\mu _{n\_{}{\textit {eff}}}$ , and saturation velocity, ${v}_{\textit {sat}}$ for fabricated InxGa $_{{1}-{x}}$ As Quantum-Well (QW) HEMTs, correlating the carrier transport properties to the device characteristics. This helps illuminate the physics of the carrier transport properties of HEMTs from the mobility relevant to the velocity saturation regimes.