High transconductance InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

Pseudomorphic In0.15Ga0.85As/Al0.15Ga0.85As modulation-doped field effect transistors (MODFET's) exhibiting extremely good dc characteristics have been successfully fabricated, dc transconductance in these strained-layer structures of 270 mS/mm were measured for 1-µm gate, normally-on devices at 300 K. Maximum drain current levels are 290 mA/mm, with excellent pinch-off and saturation characteristics. The transconductance increased to 360 mS/mm at 77 K while no persistent photoconductivity or drain collapse was observed. Preliminary microwave results indicate a 300-K current gain cutoff frequency of about 20 GHz. These results are equivalent to the best GaAs/AlGaAs MODFET results and are due in part to the improved transport properties and carrier confinement in the InGaAs quantum well.     

A self-aligned In0.53Ga0.47As junction field-effect transistor grown by molecular beam epitaxy

An In0.53Ga0.47As field-effect transistor has been fabricated on MBE-grown material, using a novel self-alignment technique. This device has a dc transconductance of 60 mS/mm for a 3-µm gate length, one of the highest reported figures for such a length, and a very low gate leakage of 100 nA at -3-V gate bias.     

Characterization of InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors

High-performance pseudomorphic InyGa1-yAs/Al0.15- Ga0.85As (0.05 le y le 0.2) MODFET's grown by MBE have been characterized at dc (300 and 77 K) and RF frequencies. Transconductances as high as 310 and 380 mS/mm and drain currents as high as 290 and 310 mA/mm were obtained at 300 and 77 K, respectively, for 1-µm gate lengths and 3-µm source-drain spacing devices. Lack of persistent trapping effects,I-Vcollapse, and threshold voltage shifts observed with these devices are attributed to the use of low mole fraction AlxGa1-xAs while still maintaining 2DEG concentrations of about 1.3 × 10¹²cm^-2. Detailed microwave S-parameter measurements indicate a current gain cut-off frequency Of 24.5 GHz Wheny = 0.20, which is as much as 100 percent better than similar GaAs/AlGaAs MODFET structures, and a maximum frequency of oscillation of 40 GHz. These superior results are in part due to the higher electron velocity of InGaAs as compared with GaAs. Velocity field measurement performed up to 3 kV/cm using the magnetoresistance method indicates an electron saturation velocity of greater than 1.7 × 10⁷cm/s at 77 K fory = 0.15, which is 20 percent higher than GaAs/AlGaAs MODFET's of similar structure.     

An In0.53Ga0.47As p-channel MOSFET with plasma-grown native oxide insulated gate

We describe the operation of an In0.53Ga0.47As p-channel inversion mode MOSFET with plasma grown native oxide insulated gate. This device exhibits a transconductance of 4 mS/mm and an effective channel mobility of more than 50% of the bulk hole mobility. This device is the first demonstration of a native oxide insulated gate MOSFET in the In1-xGaxAsyP1-ymaterial system.     

In0.53Ga0.47As FET's with insulator-assisted Schottky gates

Schottky-gate FET's have been fabricated on n-type In0.53Ga0.47As using a thin interfacial silicon nitride layer between the metal and the epitaxial layer to reduce the gate leakage current. In0.53Ga0.47As was grown by molecular beam epitaxy on semi-insulating InP substrates and silicon nitride was grown by plasma-enhanced chemical vapor deposition. Devices with 1.2µm gate length and net donor doping in the mid 10¹⁶cm^-3range show dc transconductance of up to 130mS/mm. Both depletion and enhancement mode operation were observed. The effective saturation velocity of electrons in the channel is deduced to be 2.0 ± 0.5 × 10⁷cm/sec, a value 60 to 70% higher than that in GaAs MESFET's. The insulator-assisted gate technology has many advantages in fabrication flexibility and control compared with other approaches to realizing high-speed microwave and logic in FET's in In0.53Ga0.47As.     

A low-noise microwave HEMT using MOCVD

Low-noise high-electron-mobility Transistors (HEMT's) with AlGaAs/GaAs heterostructures have been successfully fabricated using normal pressure metal-organic chemical vapor deposition (MOCVD). Hall mobilities of the two-dimensional electron gas at the interface are 8030 and 14 8000 cm²/V . s at 300 and 77 K, respectively, with an undoped Al0.3Ga0.7As spacer layer of 100 Å. The HEMT's with 0.65-µm-long and 200-µm-wide gates have exhibited a noise figure of 1.13 dB with 10.8 dB of associated gain at 12 GHz, and a dc transconductance of 280 mS/mm. These values are comparable to other reported HEMT devices using molecular-beam epitaxy (MBE).     

Semiconductor-gated InGaAs/InAlAs heterostructure transistors (SISFET's)

We have successfully fabricated FET's with In0.53Ga0.47As channels, lattice-matched In0.52Al0.48As gate barriers, and n+ In0.53- Ga0.47As gates. For a barrier thickness of 600 Å and a gate length of 1.7 µm, the maximum transconductance is 250 mS/mm at T = 300 K. From gate capacitance measurements, the cutoff frequency is inferred to be ft= 15 GHz for this gate length. Self-aligned source and drain implants have been used to permit nonalloyed ohmic contacts with a characteristic resistance of 0.1 Ω.mm. The transconductance remains above 210 mS/mm for forward gate bias up to +1.0 V, confirming the usefulness of this gate structure for enhancement-mode devices.     

Multiple-channel GaAs/AlGaAs high electron mobility transistors

Multiple-channel high electron mobility transistors (HEMT's) have been designed and fabricated on GaAs/AlGaAs heterostructural material grown by molecular beam epitaxy (MBE). The sheet carrier density of the two-dimensional electron gas (2-DEG) measured at 77 K was linearly proportional to the number of high mobility electron channels, and reached 5.3 × 10¹²cm^-2for six-channel HEMT structures. Depletion-mode devices of the double-heterojunction HEMT were operated between negative pinchoff voltage and forward-biased gate voltage without any transconductance degradation. A peak extrinsic transconductance of 360 mS/mm at 300 K and 550 mS/mm at 77 K has been measured for a 1-µm gate-length double-heterojunction enhancement-mode device. An extremely high drain current of 800 mA/mm with a gate-to-drain avalanche breakdown voltage of 9 V was measured on six-channel devices.     

A study of high-speed normally off and normally on Al0.5Ga0.5As heterojunction gate GaAs FET's (HJFET)

The dc, small-signal microwave, and large-signal switching performance of normally off and normally on Al0.5Ga0.5As gate heterojunction GaAs field-effect transistors (HJFET) with submicrometer gate lengths are reported. The structure of both types of devices comprises an n-type 10¹⁷-cm^-3Sn-doped active layer on a Cr-doped GaAs substrate, a p-type 10¹⁸-cm^-3Ge-doped Al0.5Ga0.5As gate layer and a p⁺-type 5 × 10¹⁸-cm^-3Ge-doped GaAs "contact and cap" layer on the top of the gate. The gate structure is obtained by selectively etching the p⁺-type GaAs and Al0.5Ga0.5As. Undercutting of the Al0.5Ga0.5As layer results in submicrometer gate lengths, and the resulting p⁺-GaAs overhang is used to self-align the source and the drain with respect to the gate. Normally off GaAs FET's with 0.5- to 0.7-µm long heterojunction gates exhibit maximum available power gains (MAG) of about 9 dB at 2 GHz. Large-signal pulse measurements indicate an intrinsic propagation delay of 40 ps with an arbitrarily chosen 100-Ω drain load resistance in a 50-Ω microstrip circuit. Normally on FET's with submicrometer gate lengths (∼0.6 µm) having a total gate periphery of 300 µm and a corresponding dc transconductance of 20-30 mmhos exhibit a MAG of 9.5 dB at 8 GHz. The internal propagation delay time measured under the same conditions as above is about 20 ps.     

Microwave performance of a quarter-micrometer gate low-noise pseudomorphic InGaAs/AlGaAs modulation-doped field effect transistor

We report excellent dc and millimeter-wave performance in In0.15Ga0.85As/Al0.15Ga0.85As pseudomorphic modulation-doped field effect transistors (MODFET's) with 0.25-µm-length gates. Extrinsic transconductances as high as 495 mS/mm at 300 K and unprecedented power performance in the 60-GHz range were observed. Although not yet optimized, excellent low noise characteristics, 0.9 dB, with an associated gain of 10.4 dB at 18 GHz, and a noise figure of 2.4 dB with an associated gain of 4.4 dB at 62 GHz were obtained. This is the best noise performance ever reported for a MODFET in this frequency range. These results clearly demonstrate the superiority of pseudomorphic MODFET structures in high-frequency applications.     

An In0.52Al0.48As/n+-In0.53Ga0.47As MISFET with a heavily doped channel

An In0.52Al0.48As/n⁺-In0.53Ga0.47As MIS-type field-effect transistor (FET) with a channel doped at a 7 × 10¹⁷cm^-3level has been fabricated on an InP substrate. A device with a 2-µm channel length has yielded a maximum transconductance of 152 mS/mm,f_{T} = 12.4GHz, andf_{max} = 50GHz. At 10 GHz, the maximum available gain is 17.4 dB. The performance of this device shows that heavily doped channel FET's are very promising for high-frequency operation.     

Schottky barriers and ohmic contacts on n-type InP based compound semiconductors for microwave FET's

InP, and In0.73Ga0.27As0.6P0.4, and In0.53Ga0.47As lattice matched to InP are of special importance as active FET channel materials because of the high electron velocity and/or high electron mobility they offer. Using a AuGe/Ni/Au metallization system, specific contact resistances of 5 × 10^-7Ω . cm², 8 × 10^-7Ω . cm², and 5.8 × 10^-6Ω cm²were obtained for ohmic contacts on In0.53Ga0.47As, InP, and In0.89Ga0.11As0.24P0.76, respectively. Leakage currents of 10 µA at 7-V reverse bias were observed for 1 × 200-µm gates on InP. and In0.89Ga0.11As0.24P0.76FET's having a SiO2film about 50 Å thick under the gate. A thin SiO2layer underneath the gate improved the Schottky-gate I-V characteristics, but thick oxides severely degraded the microwave performance of the FET's. These excellent ohmic contacts and Schottky barriers resulted in a maximum insertion gain of 15 dB at 8 GHz and a noise figure of 2.5 dB with 8-dB gain at 7 GHz for the InP deviees. For 1.15-eV InxGa1-xAsyP1-yFET's, the resulting gain was 9 dB at 8 GHz.     

Junction field-effect transistors using In0.53Ga0.47As material grown by molecular beam epitaxy

In this article we discusss the fabrication of junction field-effect transistors (JFETs) using In0.53Ga0.47As grown p-n junction material prepared by molecular beam epitaxy (MBE). For an n-channel doping of 2 × 10¹⁶cm^-3and a gate length of 2.0µm, these devices are shown to have a transconductance of 50 mS/mm with a corresponding internal transconductance of 67 mS/mm.     

A new Ga0.47In0.53As field-effect transistor with a lattice-mismatched GaAs gate for high-speed circuits

A novel thin GaAs lattice-mismatched gate Ga0.47In0.53As field-effect transistor (LMG-FET) is reported. The device shows an extrinsic dc transconductance of 108 mS/mm for a 1.4-µm gate length and 240-µm gate width. Despite a 3.7-percent, lattice mismatch between GaAs and Ga0.47In0.53As, the LMG-FET shows stable operation even at 80°C (with a 13-percent increase in transconductances), exhibits negligible current drift, and suffers very little change in threshold voltages (<0.05 V) under illumination, This technology may find applications in high-speed lightwave transmission as well as high-speed digital circuits.     

A new Al0.3Ga0.7As/GaAs modulation-doped FET

A new Al0.3Ga0.7As/GaAs modulation-doped FET fabricated like a MESFET but operating like a JFET was successfully fabricated and tested. This new device replaces the Schottky gate of the MESFET with an n+/p+ camel diode structure, thereby allowing problems associated with the former to be overcome. The devices, which were fabricated from structures grown by molecular beam epitaxy (MBE), had a 1µm gate length, a 290µm gate width, and a 4µm channel length. The room temperature transconductance normalized to the gate width was about 95 mS/mm, which is comparable to that obtained in similar modulation-doped Schottky barrier FET's. Unlike modulation-doped Schottky barrier FET's, fabrication of this new device does not require any critical etching steps or formation of a rectifying metal contact to the rapidly oxidizing Al0.3Ga0.7As. Relatively simple fabrication procedures combined with good device performance make this camel gate FET suitable for LSI applications.     

An In0.53Ga0.47As/Si3N4n-channel inversion mode MISFET

We describe the operation of an n-channel inversion-mode In0.53Ga0.47As MISFET with a Si3N4insulating layer. This device exhibits a transconductance of 2 mS/mm, which represents an order of magnitude improvement over previously reported In0.53Ga0.47As MISFET results.     

Characteristics of submicron gate GaAs FET's with Al0.3Ga0.7As buffers: Effects of interface quality

GaAs field effect transistors (FET's) having submicron gate lengths (0.7 µm) and Al0.3Ga0.7As buffer layers were fabricated. The saturation, and particularly the pinch-off characteristics, showed a considerable dependence on the growth conditions used during preparation by molecular beam epitaxy (MBE). The structures grown at high substrate temperatures exhibited an excellent pinch-off characteristic, while those grown at low temperatures showed an inferior pinch-off characteristic. A transconductance of 160 mS/mm was obtained in all structures, regardless of the growth temperature.     

Efficient 1.06-µm emission from InxGa1-xAs electroluminescent diodes

Vapor-grown p-n junctions of InxGa1-xAs have been prepared that emit near-bandgap infrared radiation at 1.06 µm with an external quantum efficiency in excess of 1 percent at room temperature. These diodes have an electroluminescence response time of 20 ns. In addition, InxGa1-xAs injection lasers have been fabricated with threshold current densities between 2000 and 3000 A/cm²at 80 K. The importance of internal absorption losses in determining the spectral distribution and the electroluminescence efficiency at room temperature is described.     

Monolithically integrated n0.53Ga0.47As/InP direct-coupled junction field-effect transistor amplifier

Monolithic integrated In0.53Ga0.47As/InP dc-coupled amplifiers have been built using self-aligned gate junction field-effect transistors (JFET's) grown by molecular beam epitaxy (MBE). The amplifier consists of a common-source inverter stage and a source-follower buffer with diode level shifters. Using a 1-µm gate length, amplifiers with a gain of 12 dB have been fabricated.     

Self-aligned In0.53Ga0.47As/semi-insulating/n+InP junction field-effect transistors

Depletion-mode junction field-effect transistors (JFET's) with InGaAs p-n junctions grown on compensated Fe:InP or highly resistive In0.52Al0.48As isolation layers grown on n⁺-InP substrates have been fabricated using a combination of molecular-beam epitaxy and metalorganic chemical vapor deposition growth techniques. Using a self-aligned gate technology with a 1-µm gate length, devices with high transconductance (80 mS/mm), low leakage current (<100 nA), and a gate-to-source capacitance of 0.4 pF have been fabricated. This is apparently the first report where InP-based alloy FET's have been fabricated on an isolated n⁺-substrate. This structure has application to monolithically integrated photoreceivers.