SiGe pMODFETs on silicon-on-sapphire substrates with 116 GHzfmax

The dc and microwave results of Si_0.2Ge_0.8/Si_0.7Ge_0.3 pMODFETs grown on silicon-on-sapphire (SOS) substrates by ultrahigh vacuum chemical vapor deposition are reported. Devices with L_g=0.1 μm displayed high transconductance (377 mS/mm), low output conductance (25 mS/mm), and high gate-to-drain breakdown voltage (4 V). The dc current-voltage (I-V) characteristics were also nearly identical to those of control devices grown on bulk Si substrates. Microwave characterization of 0.1×50 μm² devices yielded unity current gain (f_T) and unilateral power gain (f _max) cutoff frequencies as high as 50 GHz and 116 GHz, respectively. Noise parameter characterization of 0.1×90 μm² devices revealed minimum noise figure (F_min) of 0.6 dB at 3 GHz and 2.5 dB at 20 GHz     

High-performance InGaP/InxGa1-xAs HEMT withan inverted delta-doped V-shaped channel structure

This letter reports a new and high-performance InGaP/In_xGa_1-xAs high electron mobility transistor (HEMT) with an inverted delta-doped V-shaped channel. Due to the presence of V-shaped inverted delta-doped InGaP/In_xGa_1-x As structure, good carrier confinement and a flat and wide transconductance operation regime are expected. Experimentally, the fabricated device (1×100 μm²) shows a high gate-to-drain breakdown voltage of 30 V and a high output drain saturation current density of 826 mA/mm at V_GS=2.5 V. The high transconductance expands over a very broad operation range with the maximum value of 201 mS/mm at 300 K. Meanwhile, the studied device exhibits a good microwave frequency linearity     

High reliability InGaP/GaAs HBT

Excellent long term reliability InGaP/GaAs heterojunction bipolar transistors (HBT) grown by metalorganic chemical vapor deposition (MOCVD) are demonstrated. There were no device failures (T=10000 h) in a sample lot of ten devices (L=6.4 μm ×20 μm) under moderate current densities and high-temperature testing (J_c=25 kA/cm ², V_ce=2.0 V, Junction Temp =264°C). The dc current gain for large area devices (L=75 μm ×75 μm) at 1 kA/cm² at a base sheet resistance of 240 ohms/sq (4×10 ¹⁹ cm^-3@700 Å) was over 100. The dc current gain before reliability testing (L=6.4 μm ×10 μm) at 0.8 kA/cm² was 62. The dc current gain (0.8 kA/cm²) decreased to 57 after 10000 h of reliability testing. The devices showed an f_T=61 GHz and f_max=103 GHz. The reliability results are the highest ever achieved for InGaP/GaAs HBT and these results indicate the great potential of InGaP/GaAs HBT for numerous low- and high-frequency microwave circuit applications. The reliability improvements are probably due to the initial low base current at low current densities which result from the low surface recombination of InGaP and the high valence band discontinuity between InGaP and GaAs     

High threshold uniformity, millimeter-wavep+-GaInAs/n-AlInAs/GaInAs JHEMTs

High threshold voltage uniformity p⁺-GaInAs/n-AlInAs/GaInAs millimeter-wave junction-modulated HEMT's are reported. Devices with 0.2 μm gatelength exhibit a standard deviation in threshold voltage of 13.7 mV across a 1×1.5 in² wafer. The uniformity is achieved in devices which exhibit high DC transconductance (520 mS/mm), high unity-gain cut-off frequencies: f_T (105 GHz) and f_max (exceeding 200 GHz), and low minimum noise figure (0.45 dB) with high associated gain (14.5 dB) at 12 GHz     

Very high gain millimeter-wave InAlAs/InGaAs/GaAs metamorphicHEMT's

We report the first demonstration of W-band metamorphic HEMTs/LNA MMICs using an AlGaAsSb lattice strain relief buffer layer on a GaAs substrate. 0.1×50 μm low-noise devices have shown typical extrinsic transconductance of 850 mS/mm with high maximum drain current of 700 mA/mm and gate-drain breakdown voltage of 4.5 V. Small-signal S-parameter measurements performed on the 0.1-μm devices exhibited an excellent f_T of 225 GHz and maximum stable gain (MSG) of 12.9 dB at 60 GHz and 10.4 dB at 110 GHz. The three-stage W-band LNA MMIC exhibits 4.2 dB noise figure with 18 dB gain at 82 GHz and 4.8 dB noise figure with 14 dB gain at 89 GHz, The gain and noise performance of the metamorphic HEMT technology is very close to that of the InP-based HEMT     

DC and RF performance of LP-MOCVD grownAl0.25Ga0.75As/InxGa1-xAs(x=0.15-0.28) P-HEMT's with Si-delta doped GaAs layer

Si-delta-doped Al_0.25Ga_0.75As/In_xGa_1-xAs (x=0.15-0.28) P-HEMT's, prepared by LP-MOCVD, are investigated. The large conduction band discontinuity leads to 2-DEG density as high as 2.1×10¹²/cm² with an electron mobility of 7300 cm²/V·s at 300 K. The P-HEMT's with 0.7×60 μm gate have a maximum extrinsic transconductance of 380 mS/mm, and a maximum current density of 300 mA/mm. The S-parameter measurements indicate that the current gain and power gain cutoff frequencies are 30 and 61 GHz, respectively, The RF noise characteristics exhibit a minimum noise figure of 1.2 dB with an associated gain of 10 dB at 10 GHz. Due to the efficient doping technique, the electron mobility and transconductance obtained are among the best reported for MOCVD grown P-HEMT's with the similar structure     

High performance pseudomorphic InGaP/InGaAs power HEMTs

Power transistors with a low d.c. supply voltage were demonstrated with pseudomorphic InGaP/In_0.2Ga_0.8As/GaAs heterostructure field effect transistors on GaAs substrates and 1 μm gate length technology. A current density of 200 mA mm⁻¹ and an extrinsic transconductance of 300 mS mm⁻¹ were exhibited on a 400 μm gate width process control monitor device. For a 1 cm gate width device measured at 850 MHz and V_ds = 1.3 V, state-of-the-art results, 57.4% for the PAE, 12.7 dB for the linear gain and 21.5 dBm for the output power, were obtained.     

Self-aligned SiGe NPN transistors with 285 GHz f/sub MAX/ and 207 GHz f/sub T/ in a manufacturable technology

This paper reports on SiGe NPN HBTs with unity gain cutoff frequency (f_T) of 207 GHz and an f_MAX extrapolated from Mason's unilateral gain of 285 GHz. f_MAX extrapolated from maximum available gain is 194 GHz. Transistors sized 0.12×2.5 μm² have these characteristics at a linear current of 1.0 mA/μm (8.3 mA/μm²). Smaller transistors (0.12×0.5 μm²) have an f_T of 180 GHz at 800 μA current. The devices have a pinched base sheet resistance of 2.5 kΩ/sq. and an open-base breakdown voltage BV_CEO of 1.7 V. The improved performance is a result of a new self-aligned device structure that minimizes parasitic resistance and capacitance without affecting f_T at small lateral dimensions     

High performance 0.35 μm gate-length monolithicenhancement/depletion-mode metamorphicIn0.52Al0.48As/In0.53Ga0.47As HEMTs on GaAs substrates

Monolithic integration of enhancement (E)- and depletion (D)-mode metamorphic In_0.52Al_0.48As/In_0.53Ga_0.47 As/GaAs HEMTs with 0.35 μm gate-length is presented for the first time. Epilayers are grown on 3-inch SI GaAs substrates using molecular beam epitaxy. A mobility of 9550 cm²/V-s and a sheet density of 1.12×10^{12 -2} are achieved at room temperature. Buried Pt-gate was employed for E-mode devices to achieve a positive shift in the threshold voltage. Excellent characteristics are achieved with threshold voltage, maximum drain current, and extrinsic transconductance of 100 mV, 370 mA/mm and 660 mS/mm, respectively for E-mode devices, and -550 mV, 390 mA/mm and 510 mS/mm, respectively for D-mode devices. The unity current gain cutoff frequencies of 75 GHz for E-mode and 80 GHz for D-mode are reported     

4H-SiC MESFET with 2.8 W/mm power density at 1.8 GHz

MESFET's were fabricated using 4H-SiC substrates and epitaxy. The D.C., S-parameter, and output power characteristics of the 0.7 μm gate length, 332 μm gate width MESFET's were measured. At ν_ds =25 V the current density was about 300 mA/mm and the maximum transconductance was in the range of 38-42 mS/mm. The device had 9.3 dB gain at 5 GHz and f_max=12.9 GHz. At V_ds=54 V the power density was 2.8 W/mm with a power added efficiency=12.7%     

Temperature-dependence investigation of a high-performance inverteddelta-doped V-shaped GaInP/InxGa1-xAs/GaAspseudomorphic high electron mobility transistor

A newly designed inverted delta-doped V-shaped GaInP/In_xGa_1-xAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) has been successfully fabricated and studied. For a 1×100 μm² device, a high gate-to-drain breakdown voltage over 30 V at 300 K is found. In addition, a maximum transconductance of 201 mS/mm with a broad operation regime for 3 V of gate bias (565 mA/mm of drain current density), a very high output drain saturation current density of 826 mA/mm, and a high DC gain ratio of 575 are obtained. Furthermore, good temperature-dependent performances at the operating temperature ranging from 300 to 450 K are found. The unity current gain cutoff frequency f_T and maximum oscillation frequency f_max up to 16 and 34 GHz are obtained, respectively. Meanwhile, the studied device shows the significantly wide and flat gate bias operation regime (3 V) for microwave performances     

Submicrometre gate length scaling of inversion channelheterojunction field effect transistor

The scaling to 0.5 μm of the inversion channel HFET with a single strained InGaAs quantum well is described. A unity current gain frequency of 40 GHz, g_m=205 mS/mm and V_TH=-0.34 V have been obtained for 0.5×100 μm² devices. For shorter gate lengths, threshold shifts are sizeable so that in order to scale further, modifications to the growth and processing are required     

Delta-doped AlGaN/AlN/GaN microwave HFETs grown by metalorganicchemical vapour deposition

The performance of an innovative delta-doped AlGaN/AlN/GaN heterojunction field-effect transistor (HFET) structure is reported. The epitaxial heterostructures were grown on semi-insulating SiC substrates by low-pressure metalorganic chemical vapour deposition. These structures exhibit a maximum carrier mobility of 1058 cm²/V s and a sheet carrier density of 2.35×10¹³ cm^-2 at room temperature, corresponding to a large n_s μ_n product of 2.49×10¹⁶ V s. HFET devices with 0.25 μm gate length were fabricated and exhibited a maximum current density as high as 1.5 A/mm (at V_G=+1 V) and a peak transconductance of g_m=240 mS/mm. High-frequency device measurements yielded a cutoff frequency of f_t≃50 GHz and maximum oscillation frequency f_max≃130 GHz     

Extremely high transconductance Ge/Si0.4Ge0.6p-MODFET's grown by UHV-CVD

Ge-channel modulation-doped field-effect transistors (MODFET's) with extremely high transconductance are reported. The devices were fabricated on a compressive-strained Ge/Si_0.4Ge_0.6 heterostructure with a Hall mobility of 1750 cm²/Vs (30,900 cm²/Vs) at room temperature (77 K). Self-aligned, T-gate p-MODFET's with L_g=0.1 μm displayed an average peak extrinsic transconductance (g(m_ext)) of 439 mS/mm, at a drain-to-source bias voltage (V_ds) of -0.6 V, with the best device having a value of g(m_ext)=488 mS/mm. At 77 K, values as high as g(m_ext)=687 mS/mm were obtained at a bias voltage of only V_ds=-0.2 V. These devices also displayed a unity current gain cutoff frequency (f_T) of 42 GHz and maximum frequency of oscillation (f_max) of 86 GHz at V_ds=-0.6 V and -1.0 V, respectively     

Characterization of double pulse-doped channel GaAs MESFETs

The fabrication and characterization of a double pulse-doped (DPD) GaAs MESFET grown by organometallic vapor phase epitaxy (OMVPE) are reported. The electron mobility of a DPD structure with a carrier concentration of 3×10¹⁸/cm³ was 2000 cm²/V-s, which is about 20% higher than that of a pulse-doped (PD) structure. Implementing the DPD structure instead of the conventional PD structure as a GaAs MESFET channel, the drain breakdown voltage, current gain cutoff frequency, and maximum stable gain (MSG) increase. The maximum transconductance of 265 mS/mm at a drain current density of 600 mA/mm, a current gain cutoff frequency of 40 GHz, and an MSG of 11 dB at 18 GHz were obtained for a 0.3 μm n⁺ self-aligned DPD GaAs MESFET     

Highly doped InGaP/InGaAs/GaAs pseudomorphic HEMT's with 0.35 μmgates

We fabricated 0.35-μm gate-length pseudomorphic HEMT DCFL circuits using a highly doped thin InGaP layer as the electron supply layer. The InGaP/InGaAs/GaAs pseudomorphic HEMT grown by MOVPE is suitable for short gate-length devices with a low supply voltage since it does not show short channel effects even for gate length down to 0.35 μm. We obtained a K value of 555 mS/Vmm and a transconductance g_m of 380 mS/mm for an InGaP layer 18.5 nm thick. Fabricated 51-stage ring oscillators show the basic propagation delay of 11 ps and the power-delay product of 7.3 fJ at supply voltage of V_DD of 1 V, and 13.8 ps and 3.2 fJ at V_DD of 0.6 V for gates 10 μm wide     

Short channel AlGaN/GaN MODFET's with 50-GHz fT and1.7-W/mm output-power at 10 GHz

A thin barrier-donor layer of 200 Å was used to increase the active input capacitance and improve the extrinsic current-gain cutoff frequency (f_t) of short-gate-length AlGaN/GaN MODFETs. 0.2-μm gate-length devices fabricated on such an epi-structure with sheet carrier density of ~8×10¹² cm^-2 and mobility of 1200 cm²/Vs showed a record f_t of 50 GHz for GaN based FETs. High channel saturation current and transconductance of 800 mA/mm and 240 mS/mm respectively were also achieved along with breakdown voltages of 80 V per μm gate-drain spacing. These excellent characteristics translated into a CW output power density of 1.7 W/mm at 10 GHz, exceeding previous record for a solid-state HEMT     

AlSb/InAs HEMT's for low-voltage, high-speed applications

The design, fabrication, and characterization of 0.1 μm AlSb/InAs HEMT's are reported. These devices have an In_0.4Al _0.6As/AlSb composite barrier above the InAs channel and a p ⁺ GaSb layer within the AlSb buffer layer. The HEMT's exhibit a transconductance of 600 mS/mm and an f_T of 120 GHz at V_Ds=0.6 V. An intrinsic f_T of 160 GHz is obtained after the gate bonding pad capacitance is removed from an equivalent circuit. The present HEMT's have a noise figure of 1 dB with 14 dB associated gain at 4 GHz and V_Ds=0.4 V. Noise equivalent circuit simulation indicates that this noise figure is primarily limited by gate leakage current and that a noise figure of 0.3 dB at 4 GHz is achievable with expected technological improvements. HEMT's with a 0.5 μm gate length on the same wafer exhibit a transconductance of 1 S/mm and an intrinsic f_TL_g, product of 50 GHz-μm     

An all implanted self-aligned enhancement mode n-JFET with Zn gatesfor GaAs digital applications

An all implanted self-aligned n-channel JFET fabrication process is described where Zn implantation is used to form the p⁺ gate region. A refractory metal (W) gate contact is used to allow subsequent high temperature activation of the self-aligned Si source and drain implant. 0.7 μm JFET's have a maximum transconductance of 170 mS/mm with a saturation current of 100 mA/mm at a gate bias of 0.9 V. The p⁺/n homojunction gate has a turn on voltage of 0.95 V at a current of 1 mA/mm. The drain-source breakdown voltage is 6.5 V. Microwave measurements made at a gate bias of 1 V show an f_t of 19 GHz with an f_max of 36 GHz. These devices show promise for incorporation in both DCFL and complementary logic circuits     

Current gain dependence on subcollector and etch-stop doping inInGaP/GaAs HBTs

The DC current gain dependence of InGaP/GaAs heterojunction bipolar transistors (HBTs) on subcollector and etch-stop doping is examined. Samples of InGaP/GaAs HBTs having various combinations of subcollector doping and etch-stop doping are grown, and large area 60 μm×60 (μ) HBTs are then fabricated for DC characterization. It is found that the DC current gain has a strong dependence on the doping concentration in the subcollector and the subcollector etch-stop. Maximum gain is achieved when the subcollector is doped at 6~7×10 ¹⁸ cm^-3 while the subcollector etch-stop is doped either above 6×10¹⁸ cm^-3 (current gain/sheet resistance ratio, β/R_b=0.435 at I_c=1 mA) or below 3.5×10¹⁷ cm^-3 (β/R_b=0.426~0.438 at I_c=1 mA). The data show that it is not necessary to heavily dope the subcollector etch-stop to reduce the conduction barrier and to obtain high current gain. The high current gain obtained with the low InGaP etch-stop doping concentration is attributed to the reduction of the effective energy barrier thickness due to band bending at the heterojunction between the InGaP etch-stop and the GaAs subcollector. These results show that the β/R_b of InGaP/GaAs HBTs can improve as much as 69% with the optimized doping concentration in subcollector and subcollector etch-stop