Millimeter-wave ion-implanted gradedInxGa1-xAs MESFETs grown by MOCVD

The authors present the fabrication and characterization of ion-implanted graded In_xGa_1-xAs/GaAs MESFETs. The In_xGa_1-xAs layers are grown on GaAs substrates by MOCVD (metal-organic chemical vapor deposition) with InAs concentration graded from 15% at the substrate to 0% at the surface. 0.5-μm gate MESFETs are fabricated on these wafers using silicon ion implantation. In addition to improved Schottky contact, the graded In_xGa _1-xAs MESFET achieves maximum extrinsic transconductance of 460 mS/mm and a current-gain cutoff frequency f_t of 61 GHz, which is the highest ever reported for a 0.5-μm gate MESFET. In comparison, In_0.1Ga_0.9As MESFETs fabricated with the same processing technique show an f_t of 55 GHz     

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     

W-band low-noise InAlAs/InGaAs lattice-matched HEMTs

Very low-noise 0.15-μm gate-length W-band In_0.52 Al_0.48As/In_0.53Ga_0.47As/In _0.52Al_0.48As/InP lattice-matched HEMTs are discussed. A maximum extrinsic transconductance of 1300 mS/mm has been measured for the device. At 18 GHz, a noise figure of 0.3 dB with an associated gain of 17.2 dB was measured. The device also exhibited a minimum noise figure of 1.4 dB with 6.6-dB associated gain at 93 GHz. A maximum available gain of 12.6 dB at 95 GHz, corresponding to a maximum frequency of oscillation, f_max, of 405 GHz (-6-dB/octave extrapolation) in the device was measured. These are the best device results yet reported. These results clearly demonstrate the potential of the InP-based HEMTs for low-noise applications, at least up to 100 GHz     

Wide-band transimpedance amplifiers using AlGaAs/InxGa1-xAs pseudomorphic 2-DEG FET's

Monolithic wide-band amplifiers have been demonstrated using AlGaAs/In_xGa_1-xAs/GaAs pseudomorphic two-dimensional electron-gas field-effect transistors. The amplifiers have yielded an 18.0 GHz bandwidth and a 41.8 dBΩ transimpedance gain with a feedback resistance of 100 Ω. In addition, the dependence of In mole fraction for an In_xGa_1-xAs channel layer on device and amplifier performance has been also investigated. The g_m and the f_T in a device, along with the bandwidth, the gain, and the noise performance in an amplifier, have improved as the In mole fraction is varied from 0 to 0.25     

Metamorphic InP/InGaAs heterojunction bipolar transistors on GaAssubstrate: DC and microwave performances

High-performance InP/In_0.53Ga_0.47As metamorphic heterojunction bipolar transistors (MHBTs) on GaAs substrate have been fabricated using In_xGa_1-xP strain relief buffer layer grown by solid-source molecular beam epitaxy (SSMBE). The MHBTs exhibited a dc current gain over 100, a unity current gain cutoff frequency (f_T) of 48 GHz and a maximum oscillation frequency (f_MAX) of 42 GHz with low junction leakage current and high breakdown voltages. It has also been shown that the MHBTs have achieved a minimum noise figure of 2 dB at 2 GHz (devices with 5×5 μm ² emitter) and a maximum output power of 18 dBm at 2.5 GHz (devices with 5×20 μm² emitter), which are comparable to the values reported on the lattice-matched HBTs (LHBTs). The dc and microwave characteristics show the great potential of the InP/InGaAs MHBTs on GaAs substrate for high-frequency and high-speed applications     

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     

Molecular beam epitaxy growth and characterization of InGaP/InGaAspseudomorphic high electron mobility transistors (HEMTs) having achannel layer over critical layer thickness

In_0.5Ga_0.5P/In_xGa_1-xAs (x=0.33 and 0.40), pseudomorphic high electron mobility transistors (p-HEMTs) having a channel layer over the critical layer thickness were grown on patterned and nonpatterned GaAs substrates by using a compound-source molecular beam epitaxy (MBE). Characteristics of the highly strained InGaP/In_xGa_1-xAs (x=0.33 and 0.40) p-HEMTs grown on patterned substrates were compared with those of conventional InGaP/In_0.22Ga_0.78As p-HEMTs grown on a nonpatterned substrate. The highly strained InGaP/In_0.33Ga _0.67As p-HEMT showed substantial improvements in device performances including DC (drain saturation current and transconductance), microwave (f_T and f_max), low-frequency noise (Hooge parameter), and high-frequency noise (minimum noise figure and associated gain) characteristics compared with those of the conventional InGaP/In_0.22Ga_0.78As p-HEMT. The improvements in device performances of the highly strained InGaP/In_0.33Ga_0.67As p-HEMT are attributed to the improved transport property of the high-quality highly strained In_0.33Ga_0.67As channel layer achieved by the use of the patterned substrate growth. The results indicate the potential of highly strained InGaP/In_xGa_1-xAs p-HEMTs having a channel layer in excess of the critical layer thickness grown on patterned GaAs substrates for use in high-performance microwave device applications     

Improved performance of submicrometer-gate GaAs MESFETs with an Al0.3Ga0.7As buffer layer grown by metal organicvapor phase epitaxy

Submicrometer-gate MESFETs were fabricated with a GaAs active layer and an Al_xGa_1-xAs buffer layer grown by metalorganic vapor-phase epitaxy. To investigate the effect of buffer layer composition on device performance, microwave FETs with GaAs and Al _0.3Ga_0.7As buffer layers were compared. Electron Hall mobility in the n-GaAs active layer was found to be unaffected by the Al content or carrier concentration in the buffer layer. However, a considerable improvement in the maximum available gain to as much as 5.2 dB was obtained at 26.5 GHz for FETs with a p-Al_0.3Ga_0.7 As buffer layer; this was 1.5 dB higher than the gain obtained with a p-GaAs buffer layer. The improvement is due to a 20-30% reduction in both drain conductance and drain-gate capacitance     

A 2-18 GHz low-noise/high-gain amplifier module

The effectiveness of the two-tier matrix amplifier as a very-low-noise device with very high associated gains across multioctave frequency bands is theoretically and experimentally demonstrated. Experimental modules whose topology is based on a computer-optimized design exhibit an average noise figure of F=3.5 dB with an associated average gain of G=17.8 dB across the 2-18 GHz frequency band. These state-of-the-art results were achieved with GaAs MESFETs whose minimum noise figure is F=2.2 dB at 18 GHz and whose gate dimensions are 0.25×200 μm. The design considerations and the test results are discussed in detail     

Integration of InAlGaAs/InGaAs MODFETs on MQW modulators on GaAssubstrates

An In_xAl_yGa_1-x-y device layer structure that enables the monolithic integration of In_0.25Al _0.75As/In_0.15Ga_0.85As MODFETs and In _0.25Al_0.35Ga_0.40As/In_0.25Ga _0.75As MQW modulators is reported. Current gain cutoff frequencies of 10 GHz are measured for 1 μm gate length MODFETs. MQW modulators operating at 1.05 μm demonstrate 20% transmission modulation for an applied 8 V     

8-element linear array monolithic p-i-n MODFET photoreceivers usingmolecular beam epitaxial regrowth

An 8-element linear array of single-stage integrating front-end photoreceivers using molecular beam epitaxial (MBE) regrowth was investigated. Each element consisted of a p-i-n In_0.53Ga_0.47As photodiode integrated with a selectively regrown pseudomorphic In_0.65Ga_0.35As/In_0.52Al_0.48 As MODFET. Cutoff frequencies of 1.0-μm discrete regrown MODFETs were f_t=24 GHz and f_max=50 GHz. Transconductance of the regrown MODFETs was as high as 495 mS/mm with a current density (I_ds) of 250 mA/mm. The 3-dB bandwidth of the photoreceiver was measured to be 1 GHz. The bit rate sensitivity at 1 Gb/s was -31.8 dBm for BER 10^-9 using 1.55 μm excitation for a photoreceiver with an anti-reflection coating. The single-stage amplifier exhibited up to 25 dB flatband gain of the photocurrent, and a two-stage amplifier was up to 31 dB of gain. Good uniformity between each photoreceiver element in the array was achieved. Electrical crosstalk between photoreceiver elements was estimated to be ~-34 dB     

Half-micrometer gate-length ion-implanted GaAs MESFET with 0.8-dBnoise figure at 16 GHz

Ion-implanted GaAs MESFETs with half-micrometer gate length have been fabricated on 3-in-diameter GaAs substrates. At 16 GHz, a minimum noise figure of 0.8 dB with an associated gain of 6.3 dB has been measured. This noise figure is believed to be the lowest ever reported for 0.5- and 0.25-μm ion-implanted MESFETs, and is comparable to that for 0.25-μm HEMTs at this frequency. By using the Fukui equation and the fitted equivalent circuit model, a K_f factor of 1.4 has been obtained. These results clearly demonstrate the potential of ion-implanted MESFET technology for K-band low-noise integrated circuit applications     

Ion-implanted In(x)Ga(1-x)As MESFET's on GaAssubstrate for low-cost millimeter-wave IC application

Ion-implanted In_(x)Ga_(1-x) As MESFETs on GaAs substrate are very attractive devices for ultra-high-frequency and ultra-high-speed integrated circuit applications due to the simplicity of material structure and manufacturability of ion implantation technology. The advances in ion-implanted In_(x)Ga_(1-x) As/GaAs MESFET technology are reviewed, focusing on material structures, device fabrications, manufacturability, current gain cutoff frequency, and maximum power oscillation frequency performance, as well as low noise, power, and oscillator performance in the millimeter-wave frequency range     

High microwave and ultra-low noise performance of fullyion-implanted GaAs MESFETs with Au/WSiN T-shaped gate

Fully ion-implanted n⁺ self-aligned GaAs MESFETs with high microwave and ultra-low-noise performance have been fabricated. T-shaped gate structures composed of Au/WSiN are employed to reduce gate resistance effectively. A very thin and high-quality channel with high carrier concentration can be formed by adopting the optimum annealing temperature for the channel, and the channel surface suffers almost no damage by using ECR plasma RIE for gate formation. GaAs MESFETs with a gate length as short as 0.35 μm demonstrated a maximum oscillation frequency of 76 GHz. At an operating frequency of 18 GHz, a minimum noise figure of 0.81 dB with an associated gain of 7.7 dB is obtained. A K_f factor of 1.4 estimated by Fukui's noise figure equation, which is comparable to those of AlGaAs/GaAs HEMTs with the same geometry, reveals that the quality of the channel is very high     

Characterization of surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobilitytransistors

High-performance 0.3-μm-gate-length surface-undoped In_0.52 Al_0.48As/In_0.53Ga_0.47As/InP high-electron-mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) have been characterized and compared with a surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMTs is obtained due to the improved g_m/g₀ ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3-×150-μm-gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. It is demonstrated that the surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance. Several millimeter-wave coplanar waveguide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. A high gain per stage distributed amplifier with 170-dB±1-dB small-signal gain across a frequency band of 24-40 GHz, a W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and a broad bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures     

Demonstration of aluminum-free metamorphic InP/In0.53Ga0.47As/InP double heterojunction bipolar transistors on GaAssubstrates

We report, for the first time, the successful fabrication of aluminum-free metamorphic (MM) InP/In_0.53 Ga_0.47 As/InP double heterojunction bipolar transistors (DHBTs) on GaAs substrates with a linearly graded In_xGa_1-xP buffer grown by solid-source molecular beam epitaxy (SSMBE). Devices with 5×5 μm² emitters display a peak current gain of 40 and a common-emitter breakdown voltage (BV_CE0) higher than 9 V, a current gain cut-off frequency (f_T) of 48 GHz and a maximum oscillation frequency (f_max) of 42 GHz. A minimum noise figure of 2.9 dB and associated gain of 19.5 dB were measured at a collector current level of 2.6 mA at 2 GHz. Detailed analysis suggests that the degradation of the base-emitter heterojunction interface and the increase of bulk recombination are the most probable causes for the poorer device performance of current metamorphic HBTs compared with lattice-matched HBTs     

Low-temperature microwave characteristics of pseudomorphic InxGa1-xAs/In0.52Al0.48Asmodulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In_xGa_1-xAs/In_0.48As (x=0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency ( f_T) for the In_xGa_1-xAs/In_0.52Al_0.48As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x=0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31% increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures     

InGaP/InGaAs HFET with high current density and high cut-offfrequencies

Doped channel pseudomorphic In_0.49Ga_0.51P/In _0.20Ga_0.80As/GaAs heterostructure field effect transistors have been fabricated on GaAs substrate with 0.25 μm T-gates and self-aligned ohmic contact enhancement. By introducing the channel doping and reducing the series resistances, a high current density of 500 mA/mm is obtained in combination with cut off frequencies of f_T=68 GHz and f_max=160 GHz. The channel doping did not affect the RF-performance of the device essentially, which is additionally reflected in noise figures below 1.0 dB with an associated gain of 14.5 dB at 12 GHz     

110-120-GHz monolithic low-noise amplifiers

The authors discuss the development of 110-120-GHz monolithic low-noise amplifiers (LNAs) using 0.1-mm pseudomorphic AlGaAs/InGaAs/GaAs low-noise HEMT technology. Two 2-stage LNAs have been designed, fabricated, and tested. The first amplifier demonstrates a gain of 12 dB at 112 to 115 GHz with a noise figure of 6.3 dB when biased for high gain, and a noise figure of 5.5 dB is achieved with an associated gain of 10 dB at 113 GHz when biased for low-noise figure. The other amplifier has a measured small-signal gain of 19.6 dB at 110 GHz with a noise figure of 3.9 dB. A noise figure of 3.4 dB with 15.6-dB associated gain was obtained at 113 GHz. The authors state that the small-signal gain and noise figure performance for the second LNA are the best results ever achieved for a two-stage HEMT amplifier at this frequency band     

Direct ion-implanted 0.12 μm GaAs MESFET with ft of121 GHz and fmax of 160 GHz

An 0.12 μm gate length direct ion-implanted GaAs MESFET exhibiting excellent DC and microwave characteristics has been developed. By using a shallow implant schedule to form a highly-doped channel and an AsH₃ overpressure annealing system to optimize the shallow dopant profile, the GaAs MESFET performance was further improved. Peak transconductance of 500 mS/mm was obtained at I_ds =380 mA/mm. A noise figure of 0.9 dB with associated gain of 8.9 dB were achieved at 18 GHz. The current gain cutoff frequency f_max of 160 GHz indicates the suitability of this 0.12 μm T-gate device for millimeter-wave IC applications