High-transconductance p-channel modulation-doped AlGaAs/GaAs heterostructure FET's

p-channel modulation-doped AlGaAs-GaAs heterostructure FET's (p-HFET's) employing two-dimensional hole gas (2DHG) were fabricated under various geometrical device parameter conditions. The p-HFET characteristics were measured at 300 and 77 K for the following three device-parameter ranges: the gate length Lg(1-320 µm), the gate-source distance Lgs(0.5-5 µm), and the layer thickness dt(35-58 nm) of AlGaAs beneath the gate. Based on the obtained results, a high-performance enhancement-mode p-HFET was fabricated with the following parameters:L_{g} = 1µm,L_{gs} = 0.5µm, andd_{t} = 35nm. The achieved extrinsic transconductance gmwas 75 mS . mm^-1at 77 K. This experimental result indicates that a gmgreater than 200 mS . mm^-1at 77 K Can be obtained in 1-µm gate p-HFET devices.     

p-Channel MODFET's using GaAlAs/GaAs two-dimensional hole gas

p-channel MODFET's were fabricated in the GaAlAs/GaAs system and the properties of the hole gas system tested to ascertain its suitability for complementary logic. The Hall mobilities on a Ga.5Al.5As/GaAs modulation-doped hole gas structure were measured to be 3650 cm²V^-1s^-1and 54000 cm²V^-1s^-1with sheet carrier concentration of 1 × 10¹²cm^-2and 7.76 × 10¹¹cm^-2at 77 and 4.2 K, respectively. The measured transconductances of 1.5-µm gate-length MODFET's on this structure were measured to lie in the range of 28-35 mS.mm^-1at 77 K. The field mobility measured on long gate-length MODFET's was approximately 3200 cm²V^-1s^-1at 77 K. Using test structures for measuring current voltage characteristic in the hole-gas system, low field drift mobility was measured to be 3000 cm²V^-1s^-1and velocities of 3 5 × 10⁶cm.s^-1were measured at electric fields of 3-4 kV.cm^-1at 77 K. The Schottky barriers showed low leakage and a barrier height of 0.7 to 0.8 eV. Calculations indicate that transconductances of approximately 100 mS.mm^-1should be achievable in this system for similar gate lengths.     

Normally-off InGaAs junction field-effect transistor with InGaAs buffer layer

InGaAs junction field-effect transistors (JFET's) with 1-µm gate length were successfully fabricated with an n⁺-InGaAs active layer (8 × 10¹⁶cm^-3) and an undoped InGaAs buffer layer grown on semi-insulating InP:Fe substrate by liquid-phase epitaxy. The device showed good pinch-off behavior with a threshold voltage of 0.25 V, a low drain current of 1 µA at zero gate-source voltage, and a very high transconductance of 553 mS/mm at room temperature. This is one of the highest transconductance values ever reported for a 1-µm gate-length FET.     

Leakage current characteristics of offset-gate-structure polycrystalline-Silicon MOSFET's

Leakage current characteristics of offset-gate-structure polycrystalline-silicon (poly-Si) MOSFET's are studied as a function of dopant concentration Noffin offset-gate regions. Leakage current markedly decreases from 1 × 10^-9to 2 × 10^-11A at VD= 10 V as Noffis varied from 1 × 10¹⁸to 1 × 10¹⁷cm^-3. A maximum ON/OFF current ratio of 10⁸is obtained at 1 × 10¹⁷cm^-3. Calculations based on a quasi-two-dimensional model indicate that the reduction of leakage current is attributable to a decrease of the maximum lateral electric field strength in the drain depletion region. An analysis of the leakage current characteristics in terms of carrier emission from grain-boundary traps implies that thermonic emission accompanied by thermally assisted tunneling could be the dominant mechanism in determining leakage current.     

An investigation of i-AlGaAs/n-GaAs doped-channel MIS-like FET's (DMT's)—Properties and performance potentialities

Doped-channel MIS-like FET's (DMT's) based upon an i-AlGaAs/n-GaAs structure have been investigated in detail for the purpose of clarifying their properties and performance potentialities. The DMT is unique in having two operation modes, a depletion-layer modulation mode and an electron accumulation mode, both of which are experimentally demonstrated through capacitance-voltage characteristics. Analytical and experimental results shows that the maximum drain current IDSmaxis more than 2.5 times that for a conventional n-AlGaAs/GaAs 2DEGFET. gmmaxand IDsmaxvalues obtained for 0.5- µm gate DMT's are very high, 310 mS/mm (410 mS/mm) and 650 mA/mm (800 mA,/mm) at 300 K (77 K), respectively, fmaxis 48 GHz. fTis as large as 45 GHz, which is the best data ever reported in 0.5-µm gate FET's. Moreover, the estimated electron saturation velocity is outstandingly large, 1.5 × 10⁷cm/s (2 × 10⁷cm/s) at 300 K (77 K), even for a thin GaAs channel layer with a 3 × 10¹⁸cm^-3doping level, while Hall electron mobility is not reasonably so high, being typically 1850 cm²/V . s (1650 cm²/V . S). Preliminary power performances are also studied at 28.5 GHz. An 18-dBm (225-mW/mm) saturation output power, 6.4-dB linear gain, and 15-percent power added efficiency are achieved. A further performance improvement may be easily accomplished by gate length reduction, structure optimization, and so on. Consequently, it has been proved that DMT's have great feasibility for high-speed and high-frequency high-power device applications.     

Electronic properties of the silicon-thermally grown tantalum oxide interface

MOS capacitance measurements showed that the Si-Ta2O5interface prepared by thermal oxidation at ∼530°C of vacuum deposited Ta film followed by a heat treatment at 350°C in N2-H2is characterized by a negative "oxide" charge (6 × 10¹¹e/cm^-2at flat-band) and by an interface state density of ∼ 1 × 10¹²cm^-2(eV)^-1. The room temperature instability is small. The breakdown strength is >8 × 10⁶V/cm.     

A stable indium-phosphide diffused junction field-effect transistorwith high gain and low leakage

The fabrication and performance of a JFET which is made by diffusing zinc into an epitaxial channel of indium phosphide grown by MOCVD on a semi-insulating InP(Fe) substrate are presented. The total gate length is 2.4 μm. At 0-V gate bias the transconductance is 140 mS/mm, the gate-source capacitance is 3.0 pF/mm, and the output conductance is less than 0.5 mS/mm. At -2-V gate bias the leakage from gate to source is 4 nA/mm. The drift in drain-source current is less than ±1% after 10⁶ s under continual DC bias     

Fully implanted InP JFET with an abrupt p+-n junction

We report the first fully implanted InP junction field-effect transistor (JFET) with an abrupt p⁺-n junction. The device was made on a semi-insulating InP substrate with Si⁺⁺implant for the n-channel and Be/P co-implant for the p⁺-region. A novel self-aligned process was used to reduce the gate-source spacing and thus minimize the series resistance. Good pinch-off characteristics and very low gate leakage current were obtained. The extrinsic transconductance is approximately 40 mS/mm for a gate length of 5 µm and a channel doping of 6 × 10¹⁶/cm³.     

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.     

Properties of ion-implanted junctions in mercury—cadmium—telluride

The formation of n-p junctions by ion-implantation in Hg0.71Cd0.29Te is shown to be a result of implantation damage. n-p photodiodes have been made by implantation of Ar, B, Al, and P in a p-type substrate with acceptor concentration of 4 × 10¹⁶cm^-3. The implanted n-type layer is characterized by sheet electron concentration of 10¹⁴to 10¹⁵cm^-2and electron mobility higher than 10³cm². V^-1. s^-1, for ion doses in the range 10¹³-5 × 10¹⁴cm^-2. The photodiodes have a spectral cutoff of 5.2 µm, quantum efficiency higher than 80 percent, and differential resistance by area product above 2000 Ω . cm²at 77 K. The temperature dependence of the differential resistance is discussed. The junction capacitance dependence on reverse voltage fits a linearly graded junction model. Reverse current characteristics at 77 K have been investigated using gate-controlled diodes. The results suggest that reverse breakdown is dominated by interband tunneling in field-induced junctions at the surface, for both polarities of surface potential.     

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.     

Modulation-doped MBE GaAs/n-AlxGa1-xAs MESFETs

Modulation-doped GaAs/n-Al0.3Ga0.7As MESFETs have been fabricated. At 77 K, DC transconductance of 160 mS mm^-1was observed, which is the highest transconductance value ever reported in this type of structure. The intrinsic transconductance was calculated to be 350 mSmm^-1, and the corresponding average electron drift velocity is 1.8 × 10⁷cm s^-1, which demonstrates the real advantage of this type of device in high-speed applications.     

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.     

Silicon Oxide enhanced Schottky gate In0.53Ga0.47As FET's with a self-aligned recessed gate structure

We present the fabrication and characterization of an In0.53Ga0.47As enhanced Schottky gate FET with a self-aligned recessed gate structure. A thin layer of e-beam evaporated silicon oxide was used to reduce the gate leakage current. For a n-channel doping of 8 × 10¹⁶cm^-3and a gate length of 1.5 µm, these devices showed good pinchoff characteristics with transconductances of 150 mS/mm. The effective velocity of electrons at current saturation is deduced to be 2.4 × 10⁷cm/s at the drain end of the gate. At 3 GHz these devices have a maximum available gain of 10 dB, decreasing to 6 dB at 6 GHz.     

Double heterostructure Ga0.47In0.53As MESFETs by MBE

Ga0.47In0.53As MESFETs have been fabricated on InP substrates. The low barrier height of Ga0.47In0.53As (0.20 eV) which makes simple GaInAs MESFETs at this composition impractical, has been overcome by using thin Al0.48In0.52As layers between gate metal and GaInAs active layers. Al0.48In0.52As has also been exploited in the form of buffer layers. The double heterostructure FET wafers with single crystal Al gate metal were grown by molecular beam epitaxy (MBE). The 2.75 µm gate length MESFETs showed d.c. transconductance gm= 57 mS mm^-1in spite of nonoptimized dimensions.     

High-transconductance InAs/AlSb heterojunction field-effecttransistors with δ-doped AlSb upper barriers

The authors report the fabrication and temperature-dependent characterization of InAs/AlSb quantum-well heterojunction field-effect transistors (HFETs). Devices with electron sheet concentrations of 3.8×10¹² cm^-2 and low-field electron mobilities of 21000 cm²/V-s have been realized through the use of Te δ-doping sheets in the upper AlSb barrier. One device with a 2.0-μm gate length showed a peak extrinsic transconductance of 473 mS/mm at room temperature. Gate leakage current, operating current density, and extrinsic transconductance were found to decrease with decreasing temperature     

Gate noise in field effect transistors at moderately high frequencies

At higher frequencies the gate noise of a field effect transistor increases rapidly with increasing frequency. This effect is here attributed to the thermal noise of the conducting channel and is caused by the capacitive coupling between the channel and the gate. The noise is represented by gate and drain noise current generators igand id, respectively; an approximation method is developed that allows calculation of ig², id²and ig× idfor moderately high frequencies. The correlation coefficient of igand idis imaginary and amounts to about 0.40j under saturated conditions, ig²can be expressed in terms of the noise resistance Rn, and the gate-source capacitance Cgs.It is shown that the correlation has only a slight influence on the noise figure F and that (Fmin- 1) varies as ωCgsRnover a wide frequency range.     

Quantum-well p-channel AlGaAs/InGaAs/GaAs heterostructureinsulated-gate field-effect transistors with very high transconductance

Quantum-well p-channel pseudomorphic AlGaAs/InGaAs/GaAs heterostructure insulated-gate field-effect transistors with enhanced hole mobility are described. The devices exhibit room-temperature transconductance, transconductance parameter, and maximum drain current as high as 113 mS/mm, 305 mS/V/mm, and 94 mA/mm, respectively, in 0.8-μm-gate devices. Transconductance, transconductance parameter, and maximum drain current as high as 175 mS/mm, 800 mS/V/mm, and 180 mA/mm, respectively were obtained in 1-μm p-channel devices at 77 K. From the device data hole field-effect mobilities of 860 cm²/V-s at 300 K and 2815 cm²/V-s at 77 K have been deduced. The gate current causes the transconductance to drop (and even to change sign) at large voltage swings. Further improvement of the device characteristics may be obtained by minimizing the gate current. To this end, a type of device structure called the dipole heterostructure insulated-gate field-effect transistor is proposed     

SiGe pMOSFET's with gate oxide fabricated by microwave electroncyclotron resonance plasma processing

A new process, electron cyclotron resonance (ECR) microwave plasma oxidation, has been developed to produce a gate-quality oxide directly on SiGe alloys. One μm Al gate Si_0.86Ge_0.15 p-metal-oxide-semiconductor field-effect-transistors (pMOSFET's) with ECR-grown gate oxide have been fabricated. It is found that saturation transconductance increases from 48 mS/mm at 300 K to 60 mS/mm at 77 K. Low field hole mobilities of 167 cm²/V-s at 300 K and 530 cm ²/V-s at 77 K have been obtained     

AlGaAs/GaAs 2-DEG FET's fabricated from MO-CVD Wafers

A transconductance (gm) of as high as 330 mS/mm is obtained from wafers grown by MO-CVD in which triethyl gallium and triethyl aluminum are used as organometallic compounds. A comparison between the experimental and theoretical results is made for the dependence of gmon the thickness of the AlGaAs layer. The saturation of velocity of 2-DEG determined from the drain I-V characteristics is found to be as high as 2 × 10⁷cm/s regardless of the absence of the undoped spacer layer.