GaAs MESFET device dependences on ion-implant tilt and rotationangles

Lightly Cr-doped liquid-encapsulated Czochralski (LEC) GaAs wafers were implanted with 5×10¹² 100-keV Si²⁹ ions/cm² at tilt angles between 0 and 13° and at rotation angles between 0 and 45°C. Capacitance-voltage measurements were then made to determine electron profiles. It was found that cross-wafer device uniformity can be improved using implant tilt angles greater than 9°. For microwave MESFET devices, the maximum transconductances at low I_DS are achieved using tilt angles greater than 6° and rotation angles greater than 30°     

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     

Submicron p-channel (Al,Ga)As/(In,Ga)As HIGFETs

Submicron p-channel (Al,Ga)As/(In,Ga)As HIGFETs have been optimized for application to high-performance complementary GaAs circuits. Major issues with submicron and deep submicron (L_g⩽0.5-μm) P-channel HIGFETs have been the severe short-channel effects, such as high subthreshold leakage currents and high output conductances. With optimization of the p-type self-aligned implant schedule, control of impurity contamination at the substrate/buffer interfaces and increase of the resistivity of the unintentionally-doped GaAs buffers, high-performance submicron devices have been realized. Typically, 0.5-μm P-HIGFETs yielded room temperature transconductances of 90 mS/mm, drain currents at V_gs =V_ds=-1.5 V of 63 mA/mm, and subthreshold leakage currents near 1 nA. Subthreshold slope of 90 mV/decade and output conductances under 5 mS/mm were realized     

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     

Low emitter resistance GaAs based HBT's without InGaAs caps

Low emitter resistance is demonstrated for AlGaAs/GaAs heterojunction bipolar transistors using Pd/Ge contacts on a GaAs contact layer. The contact resistivity to 2-10×10¹⁸ cm ^-3 n-type GaAs is 4-1×10^-7 Ω-cm² . These are comparable to contact resistivities obtained with non-alloyed contacts on InGaAs layers. The non-spiking Pd/Ge contact demonstrates thermal stability and area independent resistivity suitable for scaled devices. The substitution of Pd/Ge for AuGe/Ni GaAs emitter and collector contacts reduced by an order of magnitude the emitter-base offset voltage at high current densities and increased f_t by more than 15% with significantly improved uniformity for devices with 2 and 2.6 μm wide emitters having lengths two, four and six times the width     

Effects of displaced p-n junction of heterojunction bipolartransistors

Two-dimensional simulations that demonstrate the effects of displacements of the p-n junctions from the heterojunctions of symmetrical Al_0.28Ga_0.72/GaAs double-heterojunction bipolar transistors (DHBTs) are reported. When the emitter and/or collector p-n junctions do not coincide with the AlGaAs/GaAs heterojunctions, the electrical characteristics are shown to be drastically altered due to changes in the potential profiles and to changes in recombination rates both in the neutral base and in the space-charge region of the emitter. The effects of a small displacement of the p-n junction from the emitter-base or the base-collector heterojunctions are examined and results for current gain β and cutoff frequency f_T are given that demonstrate enhanced performance for DHBTs with p-n junctions that are not coincident with the heterojunctions     

DC and AC characteristics ofAL0.25Ga0.75As/GaAs quantum-well delta-dopedchannel FET grown by LP-MOCVD

Al_0.25Ga_0.75As/GaAs quantum well delta-doped channel FETs (QWDFETs) have been successfully fabricated by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The FETs with a gate dimension of 1.8 μm×100 μm had a maximum extrinsic transconductance of 190 mS/mm and a maximum current density of 425 mA/mm. The device showed extremely broad transconductances around its peak. The S-parameter measurements indicated that the current gain and power gain cutoff frequencies of the device were 7 and 15 GHz, respectively. The transconductance versus gate voltage profiles showed a plateau region through a range of 1.7 V supporting spatial confinement of the electrons. These values are among the best reported for delta-doped GaAs-based FETs with a similar device geometry     

Ga0.51In0.49P/GaAs HEMT's exhibiting goodelectrical performance at cryogenic temperatures

The DC and microwave characteristics of Ga_0.51In_0.49P/GaAs HEMTs grown by metalorganic chemical vapor deposition (MOCVD) are presented. Devices with 1-μm-long gates show transconductances of 163 and 213 mS/mm at 300 and 77 K, respectively. Their maximum cutoff frequency is 17.8 GHz. Deep traps in the doped layer are evaluated at low temperature by the threshold voltage shift and current collapse phenomena. GaInP/GaAs HEMTs show no current collapse and have almost zero threshold voltage shift compared to AlGaAs/GaAs and InAlAs/InGaAs where the corresponding values are 0.5 and 0.25 V, respectively     

Sulfide treated GaAs MISFET's with gate insulator of photo-CVDgrown P3N5 film

Sulfide passivated GaAs MISFET's with the gate insulator of photo-CVD grown P₃N₅ films have been successfully fabricated. The device shows the drain current instability less than 22% for the period of 1.0 s ~1.0×10⁴ s, due to excellent properties of sulfide treated P₃N₅/GaAs interface. The effective electron mobility and extrinsic transconductance of the device are about 1300 cm²/V·sec and 1.33 mS, respectively, at room temperature. To estimate the effects of sulfide treatment on P₃N₅/GaAs interfacial properties, GaAs-MIS diodes are also fabricated     

Gate length scaling in high performance InGaP/InGaAs/GaAs pHEMTs

The performance of InGaP-based pHEMTs as a function of gate length has been examined experimentally. The direct-current and microwave performance of pHEMTs with gate lengths ranging from 1.0-0.2 μm has been evaluated. Extrinsic transconductances from 341 mS/mm for 1.0 μm gate lengths to 456 mS/mm for 0.5 μm gate lengths were obtained. High-speed device operation has been verified, with f_t of 93 GHz and f_max of 130 GHz for 0.2 μm gate lengths. The dependence of DC and small-signal device parameters on gate length has been examined, and scaling effects in InGaP-based pHEMT's are examined and compared to those for AlGaAs/InGaAs/GaAs pHEMTs. High-field transport in InGaP/InGaAs heterostructures is found to be similar to that of AlGaAs/InGaAs heterostructures. The lower ϵ_r of InGaP relative to AlGaAs is shown to be responsible for the early onset of short-channel effects in InGaP-based devices     

Effect of heating on the structure of Au/GaAs encapsulated with SiO2

The structural effects of heating 1500 Å Au/GaAs (001) encapsulated with 2000 Å of SiO₂ were examined by scanning electron microscopy and X-ray diffraction. It was observed that SiO₂/Au/GaAs (capped) in vacuum up to 500°C remained shiny and gold in color, whereas similar heating of Au/GaAs (uncapped) caused a change of color from shiny gold to dull silver. Furthermore, mass spectroscopy showed that the amount of arsenic vapor evolved was much less for the capped sample. However, X-ray diffraction showed that Au₇Ga₂ formed abundantly in both types of samples after heating at 500°C, though the epitaxial relationship was mainly Au₇Ga₂ (001) GaAs (001) for capped and Au₇Ga₂ (100) GaAs (001) for uncapped. SEM revealed gold-rich aligned rectangular protrusions on the surfaces of SiO₂/Au/GaAs as well as Au/GaAs after heating at 500°C, though the average length of these rectangles was 1.5 μm for the capped sample and 6.7 μm for the uncapped sample. Moreover, new morphological features absent in Au/GaAs were observed in SiO₂/Au/GaAs. These features are a gold-rich maze with a line width of μm and gold-rich protruded lines with a line width of 9 μm. The gold-rich protruded lines were formed by the growth and joining together of some gold-rich aligned rectangular protrusions. The gold-rich maze was observed in SiO₂/Au/GaAs after heating in vacuum, but was not observed in SiO₂/Au/GaAs after heating in nitrogen.     

10-μm GaAs/AlGaAs multiquantum well scanned array infraredimaging camera

A long-wavelength infrared imaging camera that uses a GaAs/Al_xGa_1-xAs quantum-well infrared photodetector (QWIP) array is demonstrated. Excellent noise equivalent temperature difference sensitivity (NEΔT<0.1°C) has been achieved. The long-wavelength cutoff for the QWIP used in this camera is at λ _c=10.7 μm with the peak response being at λ_p =9.8 μm. A peak detectivity of 2×10¹⁰ cm√Hz/W has been achieved at 77 K as well as an excellent pixel-to-pixel uniformity of 2%. Since GaAs has a more mature growth and processing technology as well as higher uniformity than HgCdTe, it shows great promise for the fabrication of large two-dimensional arrays     

Super low noise InGaP gated PHEMT

Very high performance InGaP/InGaAs/GaAs PHEMTs will be demonstrated. The fabricated InGaP gated PHEMTs devices with 0.25 × 160/cm² and 0.25 × 300 μm² of gate dimensions show 304 mA/mm and 330 mA/mm of saturation drain current at V_GS = 0 V, V_DS = 2 V, and 320 mS/mm and 302 mS/mm of extrinsic transconductances, respectively. Noise figures for 160 μm and 300 μm gate-width devices at 12 GHz are measured to be 0.46 dB with a 13 dB associated gain and 0.49 dB with a 12.85 dB associated gain, respectively. With such a high gain and low noise, the drain-to-gate breakdown voltage can be larger than 11 V. Standard deviation in the threshold voltage of 22 mV for 160 μm gate-width devices across a 4-in wafer can be achieved using a highly selective wet recess etching process. Good thermal stability of these InGaP gated PHEMTs is also presented     

Reactor characterization for a process to etchSi3N4 formed on thin SiO2

A plasma etching process for patterning LPCVD (low-pressure chemical vapor deposition) Si₃N₄ which has been formed on thin thermally grown SiO₂ has been developed and characterized with an Applied Materials 8110 batch system using 100-mm-diameter silicon wafers. To fulfill the primary process objectives of minimal critical dimension (CD) loss (~0.08 μm), vertical profiles after etch, retention of some of the underlying thermal SiO₂, and batch etch uniformity, the reactor has been characterized by evaluating the effects of variation of reactor pressure (15 to 65 mTorr), O₂ concentration by flow rate (30 to 70%) of an O₂/CHF₂ mixture, and DC bias voltage (-200 to -550 V). Analysis of the resulting etch rate, etch uniformity, dimensional, and profile data suggests that satisfactory processing may be achieved at low reactor pressure (~25 mTorr), 50-60% O₂ by flow rate in O₂/CHF₃, and low DC bias (-200 to -250 V)     

DC and AC characteristics of delta-doped GaAs FET

Molecular-beam-epitaxy-grown GaAs field-effect transistors (FETs) using a delta-doped channel are discussed. FETs having gate lengths of 1.3 μm showed transconductances as high as 290 mS/mm at a current density of 200 mA/mm. The measured f_T was 14.5 GHz and the extracted f_max was 30 GHz. These results are the best reported in a FET with this material structure having a delta-doped channel     

Extremely high peak specific transconductance AlGaAs/GaAsheterojunction bipolar transistors

Self-aligned AlGaAs/GAs heterojunction bipolar transistors with peak specific transconductances as high as 25 mS/μm² of emitter area are discussed. These are the highest specific transconductances ever reported for a bipolar transistor. These devices, which contain no indium in the emitter, display specific parasitic emitter resistances of less than 1×10^-7 Ω-cm². This low parasitic resistance is attributed to an improved n-type contact technology, in which a molybdenum diffusion barrier and a plasma-enhanced chemical vapor deposition SiO₂ overlayer are used to achieve low specific contact resistivities     

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.     

Realization of n-channel and p-channel high-mobility (Al,GA)As/GaAs heterostructure insulating gate FET's on a planar wafer surface

Self-aligned gate by ion implantation n-channel and p-channel high-mobility (Al,Ga)As/GaAs heterostructure insulated-gate field-effect transistors (HIGFET's) have been fabricated on the same planar wafer surface for the first time. Enhancement-mode n-channel (Al,Ga)As/GaAs HIGFET's have demonstrated extrinsic transconductances of 218 mS/mm at room temperature and 385 mS/mm at 77 K. Enhancement-mode p-channel (Al,Ga)As/GaAs HIGFET's have demonstrated extrinsic transconductances of 28 mS/mm at room temperature and 59 mS/mm at 77 K. There are the highest transconductance values ever reported on a p-channel FET device.     

Stable gallium arsenide MIS capacitors and MIS field effecttransistors by (NH4)2Sx treatment andhydrogenation using plasma deposited silicon nitride gate insulator

The beneficial effects of sulfur passivation of gallium arsenide (GaAs) surface by (NH₄)₂S_x chemical treatment and by hydrogenation of the insulator-GaAs interface using the plasma-enhanced chemical vapor-deposited (PECVD) silicon nitride gate dielectric film as the source of hydrogen are illustrated by fabricating Al/PECVD silicon nitride/n-GaAs MIS capacitors and metal insulator semiconductor field effect transistors (MISFET). Post metallization annealing (PMA) at temperatures in the range 450-550°C is shown to be the key process for achieving midgap interface state density below 10 ¹¹/cm²/eV and maximum incremental transconductance, which is about 75% of the theoretical maximum limit. MIS capacitors are fabricated on (NH₄)₂S_x treated GaAs substrate using gate dielectrics such as PECVD SiO ₂ and silicon oxynitride to demonstrate that the PMA is less effective with these dielectrics because of their lower hydrogen content. The small signal AC transconductance, g_ms measurements on MISFETs fabricated using silicon nitride, have shown that the low-frequency degradation of g_ms is almost absent in the devices fabricated on (NH₄)₂S_x-treated GaAs substrates and subjected to PMA. The drain current stability in these devices is demonstrated to be excellent, with an initial drift of only 2% of the starting value. The dual role of silicon nitride layer, namely, protection against loss of sulfur and an excellent source of hydrogen for additional surface passivation along with sulfur is demonstrated by comparing the transconductance of MISFETs fabricated on GaAs substrates annealed without the nitride cap after the (NH₄)₂S _x treatment     

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