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     

Effects of neutral buried p-layer on high-frequency performance ofGaAs MESFETs

Fully ion-implanted n⁺ self-aligned GaAs MESFETs with Au/WSiN refractory metal gates have been fabricated by adopting neutral buried p-layers formed by 50-keV Be-implantation. S-parameter measurements and equivalent circuit fittings are discussed. When the Be dose is increased from 2×10¹² cm^-2 to 4×10¹² cm^-2, the maximum value of the cutoff frequency with a 0.2-μm gate falls off from 108 to 78 GHz. This is because a neutral buried player makes the intrinsic gate-source capacitance increase markedly, while its influence on gate-drain capacitance and gate-source fringing capacitance is negligible. The maximum oscillation frequency recovers, however, due primarily to the drain conductance suppression by the higher-concentration buried p-layer. An equivalent value of over 130 GHz has been obtained for both 0.2-μm-gate GaAs MESFETs     

GaAs MESFETs on InP substrates grown using chloride close-proximityreactor system

DC and microwave characteristics of GaAs metal-semiconductor field-effect transistors (MESFETs) on InP grown using the chloride close-proximity reactor (CPR) system are reported. The FETs have an extrinsic maximum transconductance of 210 mS/mm for a drain saturation current of 110 mA/mm, a cutoff frequency of unity current gain of 13 GHz, and a maximum frequency of oscillation of 21 GHz. The dislocation density in a 1.6-μm GaAs layer on InP is 10⁸ cm^-2 measured from cross-sectional transmission electron microscopy (TEM). The full width at half maximum of (400) reflection is 270" for a 3-μm-thick GaAs layer     

Effect of exponentially graded base doping on the performance ofGaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5×10¹⁹ cm^-3 at the emitter edge to 5×10¹⁸ cm^-3 at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1×10¹⁹ cm^-3 , the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%     

Molecular beam epitaxial GaAs/AlGaAs heterojunction bipolartransistors on (311)A GaAs substrates with all-silicon doping

The authors have investigated the characteristics and reproducibility of Si-doped p-type (311)A GaAs layers for application to heterojunction bipolar transistors (HBTs) grown by molecular beam epitaxy (MBE). The authors obtained p=2.2×10¹⁹ cm^-3 in a layer grown at 670°C. They have used all-Si doping to grow n-p-n transistors. These devices exhibit excellent DC characteristics with β=230 in a device with base doping of p=4×10¹⁸ cm^-3     

High-speed, high-current-gain p-n-p InP/InGaAs heterojunctionbipolar transistors

p-n-p InP/InGaAs heterojunction bipolar transistors (HBTs) are reported for the first time. The transistors, grown by metal organic molecular beam epitaxy (MOMBE), exhibited maximum DC current gain values up to 420 for a base doping level of 4×10¹⁸ cm^-3 . Small-signal measurements on self-aligned transistors with 3-μm×8-μm emitter area indicated the unity gain cutoff frequency value of 10.5 GHz and the inferred maximum frequency of oscillation of 25 GHz. The results clearly demonstrate the feasibility of complementary integrated circuits in the InP material system     

High-transconductance n-type Si/SiGe modulation-doped field-effecttransistors

The authors report on the fabrication and the resultant device characteristics of the first 0.25-μm gate-length field-effect transistor based on n-type modulation-doped Si/SiGe. Prepared using ultrahigh vacuum/chemical vapor deposition (UHV/CVD), the mobility and electron sheet charge density in the strained Si channel are 1500 (9500) cm²/V-s and 2.5×10¹² (1.5×10¹² ) cm^-2 at 300 K (77 K). At 77 K, the devices have a current and transconductance of 325 mA/mm and 600 mS/mm, respectively. These values far exceed those found in Si MESFETs and are comparable to the best results achieved in GaAs/AlGaAs modulation-doped transistors     

High-performance AlGaAs/GaAs SDHTs and ring oscillators grown byMBE on Si substrates

High-performance AlGaAs/GaAs selectively doped heterojunction transistors (SDHTs) and 19-stage oscillators fabricated on silicon substrates are discussed. Epitaxial layers of AlGaAs/GaAs were grown by MBE on Si substrates. The mobility of two-dimensional electron gas (2DEG) in the SDHTs was as high as 53000 cm²/V-s at 77 K for a sheet charge density of 10×1¹² cm^-2. For 1-μm-gate-length devices, maximum transconductances of 220 and 364 mS/mm were measured at 300 and 77 K, respectively, for the SDHTs. A minimum propagation delay time of 27 ps/stage at room temperature was obtained for a 19-stage direct-coupled FET logic ring oscillator with a power dissipation of 1.1 mW/stage. The propagation delay time was reduced to 17.6 ps/stage at 77 K. From microwave S-parameter measurements at 300 K, current gain and power gain cutoff frequencies of 15 and 22 GHz, respectively, were measured. These results are comparable to those obtained for SDHT technology on GaAs substrates     

Hot-electron InGaAs/InP heterostructure bipolar transistors withfT of 110 GHz

A hot-electron InGaAs/InP heterostructure bipolar transistor (HBT) is discussed. A unity-current-gain cutoff frequency of 110 GHz and a maximum frequency of oscillation of 58 GHz are realized in transistors with 3.2×3.2-μm² emitter size. Nonequilibrium electron transport, with an average electron velocity approaching 4×10⁷ cm/s through the thin (650 Å) heavily doped (p=5×10¹⁹ cm^-3) InGaAs base and 3000-Å-wide collector space-charge region, results in a transit delay of 0.5 ps corresponding to an intrinsic cutoff frequency of 318 GHz     

MBE-grown Si/SiGe HBTs with high β, fT,and fmax

Si/SiGe heterojunction bipolar transistors (HBTs) were fabricated by growing the complete layer structure with molecular beam epitaxy (MBE). The typical base doping of 2×10¹⁹ cm^-3 largely exceeded the emitter impurity level and led to sheet resistances of about 1 kΩ/□. The devices exhibited a 500-V Early voltage and a maximum room-temperature current gain of 550, rising to 13000 at 77 K. Devices built on buried-layer substrates had an f_max of 40 GHz. The transit frequency reached 42 GHz     

High-performance, 0.1 μm InAlAs/InGaAs high electron mobilitytransistors on GaAs

This letter describes the material characterization and device test of InAlAs/InGaAs high electron mobility transistors (HEMTs) grown on GaAs substrates with indium compositions and performance comparable to InP-based devices. This technology demonstrates the potential for lowered production cost of very high performance devices. The transistors were fabricated from material with room temperature channel electron mobilities and carrier concentrations of μ=10000 cm² /Vs, n=3.2×10¹² cm^-2 (In=53%) and μ=11800 cm²/Vs, n=2.8×10¹² cm^-2 (In=60%). A series of In=53%, 0.1×100 μm² and 0.1×50 μm² devices demonstrated extrinsic transconductance values greater than 1 S/mm with the best device reaching 1.074 S/mm. High-frequency testing of 0.1×50 μm² discrete HEMT's up to 40 GHz and fitting of a small signal equivalent circuit yielded an intrinsic transconductance (g_m,i) of 1.67 S/mm, with unity current gain frequency (f_T) of 150 GHz and a maximum frequency of oscillation (f_max) of 330 GHz. Transistors with In=60% exhibited an extrinsic g_m of 1.7 S/mm, which is the highest reported value for a GaAs based device     

Ultrahigh-frequency performance of submicrometer-gate ion-implantedGaAs MESFETs

A study of the high-frequency performance of short-gate ion-implanted GaAs MESFETs with gate lengths of 0.3 and 0.5 μm is discussed. Excellent DC and microwave performance have been achieved with an emphasis on the reduction of effective gate length during device fabrication. From f_t of 83 and 48 GHz for 0.3-0.5-μm gate devices, respectively, an electron velocity of 1.5×10⁷ cm/s is estimated. An f_t of 240 GHz is also projected for a 0.1-μm-gate GaAs MESFET. These experimental results are believed to be comparable to those of the best HEMTs (high-electron-mobility transistors) reported and higher than those generally accepted for MESFETs     

Heterostructure devices using self-aligned p-type diffused ohmiccontacts

Describes the use of a p-type refractory ohmic contact in ohmic self-aligned devices. The contacts are based on self-aligned diffusion of zinc-doped tungsten film. The diffusion is nearly isotropic in the vicinity of silicon nitride sidewalls, allowing self-alignment of ohmic contacts with emitters and gates. Low-resistance contacts (<10^-6 Ω·cm²) are formed both to GaAs and GaAlAs, and the lifetime of the diffused region is superior to that obtained from implantation. Heterostructure bipolar transistors (HBTs) showing high current gains (⩾50 at 2×10³ A·cm^-2 and ⩾200 at 1×10⁵ A·cm^-2 with micrometer-sized emitter widths) and p-channel GaAs gate heterostructure field-effect transistors (HFETs) showing high transconductances (78 mS/mm at 2.2-μm gate length) have been fabricated using this contact     

High-speed metal-semiconductor-metal photodiodes with Er-doped GaAs

Very high-speed MSM photodiodes have been fabricated on Er-doped GaAs over a doping range of 10¹⁸-10²⁰ cm^-3 . The impulse response (characterized by photoconductive sampling) of these diodes, with finger widths/spacings of 2 μm, has been found to be tunable over a range of about 3 ps-22 ps. Electro-optic sampling was used to characterize MSM diodes with finger widths/spacings of 0.5 μm and 1 μm on a sample with [Er]=10¹⁹ cm^-3, resulting in 3-dB bandwidths of 160 GHz and 140 GHz, respectively, corresponding to pulse widths of 2.7 ps and 3.3 ps. Correlation measurements were also done on the GaAs:Er samples, using an all-electronic Sampling Optical Temporal Analyzer (SOTA) structure     

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     

Ion-implanted high microwave power indium phosphide transistors

Encapsulated rapid thermal annealing (RTA) has been used in the fabrication of indium phosphide (InP) power metal-insulator-semiconductor field-effect transistors (MISFETs) with ion-implanted source, drain, and active channel regions. The MISFETs had a gate length of 1.4 μm. Six to ten gate fingers per device, with individual gate finger widths of 100 or 125 μm, were used to make MISFETs with total gate widths of 0.75, 0.8, or 1 mm. The source and drain contact regions and the channel region of the MISFETs were fabricated using silicon implants in semi-insulating InP at energies from 60 to 360 keV with doses from 1×10¹² to 5.6×10¹⁴ cm^-2. The implants were activated using RTA at 700°C for 30 s in N₂ or H₂ ambients using a silicon nitride encapsulant. The high-power, high-efficiency MISFETs were characterized at 9.7 GHz, and the output microwave power density for the RTA conditions used was as high as 2.4 W/mm. For a 1-W input at 9.7 GHz gains up to 3.7 dB were observed, with an associated power-added efficiency of 29%. The output power density was 70% greater than that reported for GaAs MESFETs     

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     

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     

Characteristics including electron velocity overshoot for0.1-μm-gate-length GaAs SAINT MESFET's

Short-channel effects, substrate leakage current, and average electron velocity are investigated for 0.1-μm-gate-length GaAs MESFETs fabricated using the SAINT (self-aligned implantation for n⁺-layer technology) process. The threshold-voltage shift was scaled by the aspect ratio of the channel thickness to the gate length ( a/L_g). The substrate leakage current in a sub-quarter-micrometer MESFET is completely suppressed by the buried p layers and shallow n⁺-layers. The average electron velocity for 0.1- to 0.2-μm-gate-length FETs is estimated to be 3×10⁶ cm/s from the analysis of intrinsic FET parameters. This high value indicates electron velocity overshoot. Moreover, a very high f_T of 93.1 GHz has been attained by the 0.1-μm SAINT MESFET     

Realisation of very high transconductance GaAs MESFETs

By using a model which considers velocity overshoot, it is shown that the performance of GaAs MESFETs in enhancement mode depends strongly on the geometrical and electrical characteristics of the access region between source and gate. The sheet resistance of the unrecessed epilayer, and the distance between the source-end of the recessed region and the gate, have to be as small as possible. 300 nm gate length MESFETs with very low values for these parameters were realised with an n-GaAs active layer (6×10¹⁷ cm^-3). These devices exhibit very high microwave transconductances (800 mS/mm) with good cutoff frequencies (up to 55 GHz). This result suggests that very high transconductance MESFETs can be fabricated from not-too-heavily doped active layers provided that the characteristics of the source-gate access region is properly optimised