0.2-μm gate-length atomic-planar doped pseudomorphic Al0.3Ga0.7As/In0.25Ga0.75As MODFETswith fT over 120 GHz

The authors report the DC and RF performance of nominally 0.2-μm-gate length atomic-planar doped pseudomorphic Al_0.3Ga_0.7As/In_0.25Ga_0.75As modulation-doped field-effect transistors (MODFETs) with f_T over 120 GHz. The devices exhibit a maximum two-dimensional electron gas (2 DEG) sheet density of 2.4×10¹² cm^-2, peak transconductance g _m of 530-570 mS/mm. maximum current density of 500-550 mA/mm, and peak current-gain cutoff frequency f_T of 110-122 GHz. These results are claimed to be among the best ever reported for pseudomorphic AlGaAs/InGaAs MODFETs and are attributed to the high 2 DEG sheet density, rather than an enhanced saturation velocity, in the In_0.25Ga_0.75As channel     

In0.5(AlxGa1-x)0.5HEMTs for high-efficiency low-voltage power amplifiers: design,fabrication, and device results

In_0.5(Al_xGa_1-x)_0.5 high electron-mobility transistors (HEMTs) are expected to have higher two-dimensional electron gas density and larger current drive capability than both Al_0.23Ga_0.77As and In_0.5Ga _0.5P HEMTs due to the improved conduction-band offsets. In this paper, we performed a systematic investigation of the electrical properties of In_0.5(Al_xGa_1-x)_0.5 P (0⩽x⩽1) material system lattice matched to GaAs. By considering the conduction-band offset, direct-to-indirect-band electron transfer, donor-related deep levels, and Schottky barrier height, a relatively narrow range of the Al content 0.2⩽x⩽0.3 was found to be the optimum for the design of In_0.5(Al_xGa_1-x)_0.5 HEMTs. Under 1.2-V operation, power transistors with the optimum aluminum composition show high drain current density, high transconductance, and excellent power-added efficiency (65.2% at 850 MHz). These results demonstrate that InAlGaP HEMTs are promising candidates for high-efficiency low-voltage power applications     

Ga0.51In0.49P/In0.15Ga0.85As/GaAs pseudomorphic doped-channel FET with high-current densityand high-breakdown voltage

Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs pseudomorphic doped-channel FETs exhibiting excellent DC and microwave characteristics were successfully fabricated. A high peak transconductance of 350 mS/mm, a high gate-drain breakdown voltage of 31 V and a high maximum current density (575 mA/mm) were achieved. These results demonstrate that high transconductance and high breakdown voltage could be attained by using In_0.15Ga_0.85As and Ga_0.51In_0.49P as the channel and insulator materials, respectively. We also measured a high-current gain cut-off frequency f_t of 23.3 GHz and a high maximum oscillation frequency f_max of 50.8 GHz for a 1-μm gate length device at 300 K. RF values where higher than those of other works of InGaAs channel pseudomorphic doped-channel FETs (DCFETs), high electron mobility transistors (HEMTs), and heterostructure FETs (HFETs) with the same gate length and were mainly attributed to higher transconductance due to higher mobility, while the DC values were comparable with the other works. The above results suggested that Ga_0.51In_0.49P/In_0.15Ga_0.85 As/GaAs doped channel FET's were were very suitable for microwave high power device application     

Metamorphic In0.4Al0.6As/In0.4Ga0.6As HEMTs on GaAs substrate

New In_0.4Al_0.6As/In_0.4Ga_0.6 As metamorphic (MM) high electron mobility transistors (HEMTs) have been successfully fabricated on GaAs substrate with T-shaped gate lengths varying from 0.1 to 0.25 μm. The Schottky characteristics are a forward turn-on voltage of 0.7 V and a gate breakdown voltage of -10.5 V. These new MM-HEMTs exhibit typical drain currents of 600 mA/mm and extrinsic transconductance superior to 720 mS/mm. An extrinsic current cutoff frequency f_T of 195 GHz is achieved with the 0.1-μm gate length device. These results are the first reported for In_0.4 Al_0.6As/In_0.4Ga_0.6As MM-HEMTs on GaAs substrate     

Device linearity improvement byAl0.3Ga0.7As/In0.2Ga0.8Asheterostructure doped-channel FETs

The linearities of pseudomorphic heterostructure Al_0.3Ga_0.7As/In_0.2Ga_0.8As doped-channel FETs (DCFETs) and HEMTs were evaluated by DC and RF testings. Due to the absence of parallel conduction in the doped-channel approach, as compared to the modulation-doped structure, a wide and flat device performance together with a high current density was achieved. This improvement of device linearity suggests that doped-channel designs are suitable for high frequency power device application     

Enhancement-mode power heterojunction FET utilizingAl0.5Ga0.5As barrier layer with negligibleoperation gate current for digital cellular phones

We have developed a novel enhancement-mode double-doped AlGaAs/InGaAs/AlGaAs heterojunction FET (HJFET) with a 5 nm thick Al_0.5Ga_0.5As barrier layer inserted between an In _0.2Ga_0.8As channel layer and an upper Al_0.2 Ga_0.8As electron supply layer. The Al_0.5Ga _0.5As barrier layer reduces gate current under high forward gate bias voltage, resulting in a high forward gate turn-on voltage (V _F) of 0.87 V, which is 170 mV higher than that of an HJFET without the barrier layer. Suppression of gate current assisted by a parallel conduction path in the upper electron supply layer was found to be also important for achieving the high V_F. The developed device exhibited a high maximum drain current of 300 mA/mm with a threshold voltage of 0.17 V. A 950 MHz PDC power performance was evaluated under single 3.5 V operation. An HJFET with a 0.5 μm long gate exhibited 0.92 W output power and 63.6% power-added efficiency with 0.08 mA gate current (I_g) at -48 dBc adjacent channel leakage power at 50 kHz off-center frequency. This I_g is one-thirteenth to that of the HJFET without the barrier layer. These results indicate that the developed enhancement-mode HJFET is suitable for single low voltage operation power applications     

Characteristics of a In0.52(AlxGa1-x)0.48As/In0.53Ga0.47As(0⩽x⩽1) heterojunction and its application onHEMT's

The quaternary In_0.52(Al_xGa_1-x) _0.48As compound on InP substrates is an important material for use in optoelectronic and microwave devices. We systematically investigated the electrical properties of quaternary In_0.52(Al_xGa_1-x)_0.48As layers, and found a 10% addition of Ga atoms into the InAlAs layer improves the Schottky diode performance. The energy bandgap (E_g ) for the In_0.52(Al_xGa_1-x)_0.48As layer was (0.806+0.711x) eV, and the associated conduction-band discontinuity (ΔE_c), in the InAlGaAs/In_0.53Ga_0.47 As heterojunction, was around (0.68±0.01)ΔE_g . Using this high quality In_0.52(Al_0.9Ga_0.1)_0.48As layer in the Schottky and buffer layers, we obtained quaternary In_0.52(Al_0.9Ga_0.1)_0.48As/In _0.53Ga_0.47As HEMTs. This quaternary HEMT revealed excellent dc and microwave characteristics. In comparison with the conventional InAlAs/InGaAs HEMT's, quaternary HEMT's demonstrated improved sidegating and device reliability     

0.12 μm transferred-substrateIn0.52Al0.48As/In0.53Ga0.47As HEMTs on silicon wafer

New In_0.52Al_0.48As/In_0.53Ga_0.47 As transferred-substrate high electron mobility transistors (TS-HEMTs) have been successfully fabricated on 2-in Silicon substrate with 0.12 μm T-shaped gate length. These new TS-HEMTs exhibit typical drain currents of 450 mA/mm and extrinsic transconductance up to 770 mS/mm. An extrinsic current gain cutoff frequency f_T of 185 GHz is obtained. That result is the first reported for In_0.52Al_0.48As/In_0.53Ga_0.47 As TS-HEMTs on Silicon substrate     

RIE gate-recessed(Al0.3Ga0.7)0.5In0.5P/InGaAsdouble doped-channel FETs using CHF3+BCl3 mixingplasma

BCl₃+CHF₃ gas mixtures for the reactive ion etching process were applied to the gate-recess for fabricating (Al_0.3Ga_0.7)_0.5In_0.5P quaternary heterostructure double doped-channel FET's (D-DCFET), where a high uniformity of Vth was achieved. With the merits of this wide bandgap (Al_0.3Ga_0.7)_0.5In_0.5P layer, microwave power performance of this heterostructure D-DCFET demonstrates a compatible performance for devices fabricated on AlGaAs/InGaAs heterostructures     

High-performance In0.08Ga0.92As MESFETs onGaAs(100) substrates

In_0.08Ga_0.92As MESFETs were grown in GaAs (100) substrates by molecular beam epitaxy (MBE). The structure comprised an undoped compositionally graded In_xGa_1-x As buffer layer, an In_0.08Ga_0.92As active layer, and an n⁺-In_0.08Ga_0.92As cap layer. FETs with 50-μm width and 0.4-μm gate length were fabricated using the standard processing technique. The best device showed a maximum current density of 700 mA/mm and a transconductance of 400 mS/mm. The transconductance is extremely high for the doping level used and is comparable to that of a 0.25-μm gate GaAs MESFET with an active layer doped to 10¹⁸ cm^-3. The current-gain cutoff frequency was 36 GHz and the power-gain cutoff frequency was 65 GHz. The current gain cutoff frequency is comparable to that of a 0.25-μm gate GaAs MESFET     

Characteristics of strained In0.65Ga0.35As/In0.52Al0.48As HEMT withoptimized transport parameters

The DC and microwave performance of a strained In₀.₆₅Ga₀.₃₅As/In₀ .₅₂A1₀.₄₈As HEMT (high-electron-mobility transistors) is reported. Its design is based on theoretical and experimental studies including low- and high-field transport characterization of heterostructures with different strains. The intrinsic DC transconductance and cutoff frequence of 1.4-μm-long gate HEMTs are 574 mS/mm and 38.6 GHz, respectively. The increased indium (In) composition in the channel enhances the drift velocity from 1.35×10⁷ to 1.55×10⁷ cm/s at 300 K     

Fabrication of 0.15-μm Γ-Shaped Gate In0.52Al0.48As/In0.6Ga0.4As Metamorphic HEMTs Using DUV Lithography and Tilt Dry-Etching Technique

An In_0.52Al_0.48As/In_0.6Ga_0.4 As metamorphic high-electron mobility transistor (MHEMT) with 0.15-mum Gamma-shaped gate using deep ultraviolet lithography and tilt dry-etching technique is demonstrated. The developed submicrometer gate technology is simple and of low cost as compared to the conventional E-beam lithography or other hybrid techniques. The gate length is controllable by adjusting the tilt angle during the dry-etching process. The fabricated 0.15-mum In_0.52Al_0.48As/In_0.6Ga_0.4As MHEMT using this novel technique shows a saturated drain-source current of 680 mA/mm and a transconductance of 728 mS/mm. The f_T and f_max of the MHEMT are 130 and 180 GHz, respectively. The developed technique is a promising low-cost alternative to the conventional submicrometer E-beam gate technology used for the fabrication for GaAs MHEMTs and monolithic microwave integrated circuits     

Unstrained, modulation-doped, In0.3Ga0.7As/In0.29Al0.71As field-effect transistor grown on GaAssubstrate

The fabrication, structure, and properties of unstrained modulation-doped, 1-μm-long and 10-μm-wide gate, field effect transistors made of In_0.3Ga_0.7As/In_0.29As_0.71As heterojunctions grown on GaAs substrates using compositionally step-graded buffer layers are described. These devices have a transconductance of 335 mS/mm, f_max of 56 GHz, and a gate breakdown voltage of 23.5 V     

Insulator passivation of In0.2Ga0.8As-GaAssurface quantum wells

The electronic passivation of (100) In_0.2Ga_0.8 As-GaAs surface quantum wells (QWs) using in situ deposition of an amorphous, insulating Ga₂O₃ film has been investigated and compared to standard Al_0.45Ga_0.55As passivation. Nonradiative lifetimes τ_r=1.1±0.2 and 1.2±0.2 ns have been inferred from the dependence of the internal quantum efficiency η on optical excitation density P₀' for the Ga₂O₃ and Al_0.45Ga_0.55As passivated In_0.02 Ga_0.8As-GaAs surface QW, respectively. Beyond identical internal quantum efficiency, the amorphous Ga₂O₃ insulator passivation simplifies device processing, eludes problems arising from lattice-mismatched interfaces, and virtually eliminates band bending in electronic and optoelectronic devices based on a low dimensional system such as quantum wells, wires, and dots     

Al0.25In0.75P/Al0.48In0.52As/Ga0.35In 0.65As graded channelpseudomorphic HEMT's with high channel-breakdown voltage

A new Al_0.25In_0.75P/Al_0.48In_0.52 As/Ga_0.35In 0_.65As pseudomorphic HEMT where the InAs mole fraction of the Ga_1-xIn_xAs channel was graded (x=0.53→0.65→0.53) is described. The modification of the quantum well channel significantly improved breakdown characteristics. In addition, use of an Al_0.25In_0.75P Schottky layer increased the Schottky barrier height. Devices having 0.5 μm gate-length showed g_m of 520 mS/mm and I_max of 700 mA/mm. The gate-drain (BV_g-d) and source-drain (BV_d-s ) breakdown voltages were as high as -14 and 13 V, respectively. An f_T of 70 GHz and f_max of 90 GHz were obtained     

Device linearity comparisons between doped-channel andmodulation-doped designs in pseudomorphic Al0.3Ga0.7As/In0.2Ga0.8As heterostructures

The linearities of pseudomorphic Al_0.3Ga_0.7As/In_0.2Ga_0.8As doped-channel FET's were characterized by comparing the characteristics of modulation-doped field-effect transistors (FET's) based on dc and microwave evaluations. By using an undoped high-bandgap layer beneath the gate, the so-called parasitic MESFET-type conduction, which is common in HEMT's, can therefore be eliminated in doped-channel designs. Therefore, a wide and flat device performance together with a high current driving capability can be achieved in DCFET's. This linearity improvement in device performance suggests that doped-channel designs are more suitable for application in microwave power devices     

The effect of gate recess profile on device performance ofGa0.51In0.49P/In0.2Ga0.8Asdoped-channel FET's

The effect of gate recess profile on device performance of Ga_0.51In_0.49P/In_0.2Ga_0.8As doped-channel FETs was studied. In the experiment, Ga_0.51In _0.49P/In_0.2Ga_0.8As doped-channel FETs (DCFET's) using triple-recessed gate structure were compared with devices using single-recessed and double-recessed gate structures. It is found that triple-recessed gate approach provides higher breakdown voltage (35 V) than single-recessed (16 V) and double-recessed gate (28 V) approaches. This is attributed to the larger aspect ratio in the triple-recessed gate structure. A unified method to calculate the breakdown voltages of MESFETs, HEMTs and DCFETs (or MISFETs) of any given arbitrary recessed gate profile was proposed and used to explain the experimental results     

In0.52Al0.48As/In0.53Ga0.47As MSM photodetectors and HEMT's grown by MOCVD on GaAs substrates

The authors report the first demonstration of In_0.52Al _0.48As/In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors and high-electron-mobility transistors (HEMTs) grown on GaAs substrates by organometallic chemical vapor deposition. Both photodetectors and transistors showed no degradation in performance compared to devices simultaneously grown on InP substrates. The photodetectors exhibited a responsivity of 0.45 A/W and leakage current of 10 to 50 nA. The HEMTs with a gate length of 1.0 μm showed a transconductance as high as 250 mS/mm, and f_T and f_max of 25 and 70 GHz, respectively     

Gate-length dependence of DC and microwave properties ofsubmicrometer In0.53Ga0.47As HIGFETs

In_0.52Al_0.48As/In_0.53Ga_0.47 As/InP heterostructure insulated-gate field-effect transistors (HIGFETs) with gate lengths from 1.1 and 0.3 μm have been fabricated, and their electrical performance is characterized at DC and microwave frequencies. The refractory-gate self-aligned process, applied to devices with In_0.53Ga_0.47As channels, yields an unprecedented combination of very-high speed and excellent uniformity. HIGFETs with L_g=0.6 μm showed average peak transconductance g_m of 528 mS/mm and unity-current-gain cutoff frequency f_t of 50 GHz. The uniformity of g_m was better than 1%, and the voltage of the g_m peak was uniform to ±30 mV. HIGFETs with L_g=0.3 μm showed f₁ up to 63 GHz, but suffered from serious short-channel effect, due to excessive thickness of the InGaAs channel layer. A self-aligned technique for gate resistance reduction is shown to substantially improve microwave power gain     

A Novel Dilute Antimony Channel In0.2Ga0.8AsSb/GaAs HEMT

This letter reports, for the first time, a high-electron mobility transistor (HEMT) using a dilute antimony In_0.2Ga_0.8 AsSb channel, which is grown by a molecular-beam epitaxy system. The interfacial quality within the InGaAsSb/GaAs quantum well of the HEMT device was effectively improved by introducing the surfactantlike Sb atoms during the growth of the InGaAs layer. The improved heterostructural quality and electron transport properties have also been verified by various surface characterization techniques. In comparison, the proposed HEMT with (without) the incorporation of Sb atoms has demonstrated the maximum extrinsic transconductance g_m,max of 227 (180) mS/mm, a drain saturation current density I_DSS of 218 (170) mA/mm, a gate-voltage swing of 1.215 (1.15) V, a cutoff frequency f_T of 25 (20.6) GHz, and the maximum oscillation frequency f_max of 28.3 (25.6) GHz at 300 K with gate dimensions of 1.2times200 mum²