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     

Single- and double-heterojunction pseudomorphic In0.5(Al0.3Ga0.7)0.5P/In0.2Ga0.8As high electron mobility transistors grown by gas sourcemolecular beam epitaxy

In_0.5(Al_0.3Ga_0.7)_0.5 P/In_0.2Ga_0.8As single- and double-heterojunction pseudomorphic high electron mobility transistors (SH-PHEMTs and DH-PHEMTs) on GaAs grown by gas-source molecular beam epitaxy (GSMBE) were demonstrated for the first time. SH-PHEMTs with a 1-μm gate-length showed a peak extrinsic transconductance g_m of 293 mS/mm and a full channel current density I_max of 350 mA/mm. The corresponding values of g_m and I_max were 320 mS/mm and 550 mA/mm, respectively, for the DH-PHEMTs. A short-circuit current gain (H₂₁) cutoff frequency f_T of 21 GHz and a maximum oscillation frequency f_max of 64 GHz were obtained from a 1 μm DH device. The improved device performance is attributed to the large ΔE_c provided by the In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As heterojunctions. These results demonstrated that In_0.5(Al_0.3Ga_0.7)_0.5P/In _0.2Ga_0.8As PHEMT's are promising candidates for microwave power applications     

Short pulse transfer characteristics of AlxGa1-xAs/GaAs andAlxGa1-xAs/InyGa1-yAsmodulation-doped heterojunction FET's

Short-pulse drain current versus gate voltage transfer characteristics measured for modulation-doped HFETs (MODFETs) with four donor-layer-channel-layer combinations-(1) Al_0.3Ga_0.7 As-GaAs, (2) Al_0.2Ga_0.8As-GaAs, (3) Al_0.3Ga_0.7As-In_0.2Ga_0.8As, and (4) Al_0.2Ga_0.8As-In_0.2 a_0.8 As-are compared with the DC transfer characteristics. The measurements are relevant to high-speed switching in HFET circuits. Significant shifts in threshold voltage are observed between the DC and short-pulse characteristics for the structures with n⁺-Al_0.3Ga_0.7As donor layers, while the corresponding shifts for structures with n⁺-Al_0.2Ga_0.8As donor layers are relatively small or virtually nonexistent     

High-Performance Inversion-Type Enhancement-Mode InGaAs MOSFET With Maximum Drain Current Exceeding 1 A/mm

High-performance inversion-type enhancement- mode (E-mode) n-channel In_0.65Ga_0.35As MOSFETs with atomic-layer-deposited Al₂O₃ as gate dielectric are demonstrated. A 0.4-mum gate-length MOSFET with an Al₂O₃ gate oxide thickness of 10 nm shows a gate leakage current that is less than 5 times 10^-6 A/cm² at 4.0-V gate bias, a threshold voltage of 0.4 V, a maximum drain current of 1.05 A/mm, and a transconductance of 350 mS/mm at drain voltage of 2.0 V. The maximum drain current and transconductance scale linearly from 40 mum to 0.7 mum. The peak effective mobility is ~1550 cm²/V ldr s at 0.3 MV/cm and decreases to ~650 cm²/V ldr s at 0.9 MV/cm. The obtained maximum drain current and transconductance are all record-high values in 40 years of E-mode III-V MOSFET research.     

$hbox{In}_{0.53}hbox{Ga}_{0.47}hbox{As}$ Channel MOSFETs With Self-Aligned InAs Source/Drain Formed by MEE Regrowth

Abstract-We report Al₂O₃Zln_0.53Ga_0.47As MOSFETs having both self-aligned in situ Mo source/drain ohmic contacts and self-aligned InAs source/drain n⁺ regions formed by MBE regrowth. The device epitaxial dimensions are small, as is required for 22-nm gate length MOSFETs; a 5-nm In_0.53Ga_0.47As channel with an In_0.4sAl_0.52As back confinement layer and the n⁺⁺ source/drain junctions do not extend below the 5-nm channel. A device with 200-nm gate length showed I_D = 0.95 mA/mum current density at V_GS = 4.0 V and g_m = 0.45 mS/mum peak transconductance at V_DS = 2.0 V.     

Double-dopedIn0.35Al0.65As/In0.35Ga0.65As power heterojunction FET on GaAs substrate with 1 W outputpower

A double-doped metamorphic In_0.35Al_0.65As/In _0.35Ga_0.65As power heterojunction FET (HJFET) on GaAs substrate is demonstrated. The HJFET exhibits good dc characteristics, with gate forward turn on voltage of 1.0 V, breakdown voltage of 20 V, and maximum drain current of 490 mA/mm. Under RF operation at a frequency of 950 MHz, a power added efficiency of 63% with associated output power of 31.7 dBm is obtained at a gate width of 12.8 mm. This large gate width and state-of-the-art power performance in metamorphic HJFETS were enabled by a selective etching, sputtered WSi gate process and low surface roughness due to an Al_0.60Ga_0.40As_0.69Sb_0.31 strain relief buffer     

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     

Submicrometer Inversion-Type Enhancement-Mode InGaAs MOSFET With Atomic-Layer-Deposited Al2O3 as Gate Dielectric

High-performance inversion-type enhancement-mode n-channel In_0.53Ga_0.47As MOSFETs with atomic-layer-deposited (ALD) Al₂O₃ as gate dielectric are demonstrated. The ALD process on III-V compound semiconductors enables the formation of high-quality gate oxides and unpinning of Fermi level on compound semiconductors in general. A 0.5-mum gate-length MOSFET with an Al₂O₃ gate oxide thickness of 8 nm shows a gate leakage current less than 10^-4 A/cm² at 3-V gate bias, a threshold voltage of 0.25 V, a maximum drain current of 367 mA/mm, and a transconductance of 130 mS/mm at drain voltage of 2 V. The midgap interface trap density of regrown Al₂O₃ on In_0.53Ga_0.47As is ~1.4 x 10¹²/cm² ldr eV which is determined by low-and high-frequency capacitance-voltage method. The peak effective mobility is ~1100 cm² / V ldr s from dc measurement, ~2200 cm²/ V ldr s after interface trap correction, and with about a factor of two to three higher than Si universal mobility in the range of 0.5-1.0-MV/cm effective electric field.     

High temperature performance and operation of HFETs

The high temperature performance of Al_0.75Ga_0.25 As/In_0.25Ga_0.75As/GaAs Complementary Heterojunction FETs (CHFETs) is reported between 25 and 500°C. Both experimental and modeled devices have shown acceptable digital characteristics to 400°C. Digital logic circuits have also been shown to operate at temperatures of over 400°C. This strongly suggests that GaAs based devices are capable of satisfying high temperature electronics requirements in the 125-400°C range. Two dimensional physically based modeling has been used to understand the high temperature operation of the HFETs. This work has shown that the devices suffer from gate limited drain leakage currents at elevated ambient temperatures. This off-state leakage current is higher than anticipated. Simulation has shown that, although forward gate leakage currents are reduced with the heterostructure device design, the reverse current is not     

Metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with a novelcomposite channels design

We report on fabrication and performance of novel 0.13 μm T-gate metamorphic InAlAs/InGaAs HEMTs on GaAs substrates with composite InGaAs channels, combining the superior transport properties of In_0.52Ga_0.48As with low-impact ionization in the In_0.32Ga_0.68As subchannel. These devices exhibit excellent DC characteristics, high drain currents of 750 mA/mm, extrinsic transconductances of 600 mS/mm, combined with still very low output conductance values of 20 mS/mm, and high channel and gate breakdown voltages. The use of a composite InGaAs channels leads to excellent cut-off frequencies: f_max of 350 GHz and an f_T 160 GHz at V_DS=1.5 V. These are the best microwave frequency results ever reported for any FET on GaAs substrate     

Logic Suitability of 50-nm In0.7 Ga0.3As HEMTs for Beyond-CMOS Applications

We have experimentally studied the suitability of nanometer-scale In_0.7Ga_0.3As high-electron mobility transistors (HEMTs) as an n-channel device for a future high-speed and low-power logic technology for beyond-CMOS applications. To this end, we have fabricated 50- to 150-nm gate-length In_0.7Ga_0.3As HEMTs with different gate stack designs. This has allowed us to investigate the role of Schottky barrier height (Phi_B) and insulator thickness (t_ins) on the logic characteristics of In_0.7Ga_0.3As HEMTs. The best 50-nm HEMTs with the highest Phi_B and the smallest t_ins exhibit an I_ON/I_OFF ratio in excess of 10⁴ and a subthreshold slope (S) below 86 mV/dec. These nonoptimized 50-nm In_0.7Ga_0.3As HEMTs also show a logic gate delay (CV/I) of around 1 ps at a supply voltage of 0.5 V, while maintaining an I_ON/I_OFF ratio above 10⁴, which is comparable to state-of-the-art Si MOSFETs. As one of the alternatives for beyond-CMOS technologies, we believe that InAs-rich InGaAs HEMTs hold a considerable promise.     

Modeling of short-pulse threshold voltage shifts due to DX centersin AlxGa1-xAs/GaAs and AlxGa1-xAs/InyGa1-yAs MODFET's

The DX-center-related short-pulse threshold voltage shifts (SPTVS) in Al_xGa_1-xAs-based MODFETs is modeled using CBAND, a simulator that solves Poisson equations self-consistently with Schrodinger equations and donor statistics. Using values given in the literature for the DX energy level in Al_xGa_1-xAs this technique gives good agreement between measured and simulated SPTVS for Al_0.3Ga_0.7As/GaAs and Al_0.3Ga_0.7As/In_0.2Ga_0.8As MODFETs. Both simulation and experiment show that the use of Al_0.2 Ga_0.8As in the donor layer reduces the SPTVS relative to the structures using Al_0.3Ga_0.7As. However, the measured shifts at this composition are considerably lower than the simulated values, indicating a DX energy level that may be higher than the value extrapolated from the literature, possibly due to the existence of multiple trap levels. Despite this discrepancy, these results support the use of strained-channel layers and lower Al_x Ga_1-xAs compositions in MODFETs for digital and other large-signal applications requiring good threshold stability     

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     

InAlAs/InGaAs metamorphic HEMT with high current density and highbreakdown voltage

An In_0.3Al_0.7As/In_0.3Ga_0.7 As metamorphic power high electron mobility transistor (HEMT) grown on GaAs has been developed. This structure with 30% indium content presents several advantages over P-HEMT on GaAs and LM-HEMT on InP. A 0.15-μm gate length device with a single δ doping exhibits a state-of-the-art current gain cut-off frequency F_t value of 125 GHz at V_ds=1.5 V, an extrinsic transconductance of 650 mS/mm and a current density of 750 mA/mm associated to a high breakdown voltage of -13 V, power measurements performed at 60 GHz demonstrate a maximum output power of 240 mW/mm with 6.4-dB power gain and a power added efficiency (PAE) of 25%. These are the first power results ever reported for any metamorphic HEMT     

High-breakdown AlGaAs/InGaAs/GaAs PHEMT with tellurium doping

The authors report the fabrication and characterisation of an Al _0.43Ga_0.57As/In_0.2Ga_0.8 As/GaAs pseudomorphic HEMT (PHEMT) with high channel conductivity grown by solid source MBE. The high conductivity of the channel is a direct consequence of the high sheet charge and high mobility that has recently been obtained by using tellurium as the n-type dopant in 43% AlGaAs. The device characteristics reflect the resulting reduction in the parasitic resistances of the high channel conductivity. Microwave measurements yield a short-circuit current gain cutoff frequency f_T of 11 GHz and maximum oscillation frequency f_max of 25 GHz. A high gate-drain breakdown voltage of 26 V along with a maximum drain current density of 400 mA/mm obtained in the device illustrate the applicability of this technology in microwave power field effect transistors     

DC and microwave characteristics of InAlAs/InGaAssingle-quantum-well MODFETs with GaAs gate barriers

The design and performance of In_0.53Ga_0.47As/In_0.52Al_0.48 As modulation-doped field-effect transistors (MODFETs) have been optimized by incorporating a single In_0.53Ga_0.47As quantum-well channel and a thin strained GaAs gate barrier layer. These help to lower the output conductance and gate leakage current of the device, respectively. The DC performance of 1-μm-gate devices is characterized by extrinsic transconductances of 320 mS/mm at 300 K and 450 mS/mm at 77 K and a best value of f_T=35 GHz is derived from S-parameter measurements     

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     

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     

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