Millimeter-wave high-power 0.25-/spl mu/m gate-length AlGaN/GaN HEMTs on SiC substrates

Reports on the CW power performance at 20 and 30 GHz of 0.25 /spl mu/m /spl times/ 100 /spl mu/m AlGaN/GaN high electron mobility transistors (HEMTs) grown by MOCVD on semi-insulating SiC substrates. The devices exhibited current density of 1300 mA/mm, peak dc extrinsic transconductance of 275 mS/mm, unity current gain cutoff (f/sub T/) of 65 GHz, and maximum frequency of oscillation (f/sub max/) of 110 GHz. Saturated output power at 20 GHz was 6.4 W/mm with 16% power added efficiency (PAE), and output power at 1-dB compression at 30 GHz was 4.0 W/mm with 20% PAE. This is the highest power reported for 0.25-/spl mu/m gate-length devices at 20 GHz, and the 30 GHz results represent the highest frequency power data published to date on GaN-based devices.     

High performance 0.14 /spl mu/m gate-length AlGaN/GaN power HEMTs on SiC

High electron mobility transistors (HEMTs) were fabricated from AlGaN/GaN on semi-insulating SiC substrates with excellent performance and high yield. The devices had 0.14 /spl mu/m T-gates with a total width of 300 /spl mu/m. Extrinsic, unpassivated peak performance values for these HEMTs include transconductance of 338 mS/mm, maximum drain current of 1481 mA/mm, unity current gain cutoff frequency of 91 GHz, and maximum frequency of oscillation of 122 GHz. Saturated CW power measurements of these devices at 10 GHz result in 4.6 W/mm with PAE at 46% when optimized for power and 3.0 W/mm with PAE at 65% when optimized for efficiency.     

RF noise in 0.18-/spl mu/m and 0.13-/spl mu/m MOSFETs

Studied the gate finger number and gate length dependence on minimum noise figure (NF/sub min/) in deep submicrometer MOSFETs. A lowest NF/sub min/ of 0.93 dB is measured in 0.18-/spl mu/m MOSFET at 5.8 GHz as increasing finger number to 50 fingers, but increases abnormally when above 50. The scaling gate length to 0.13 /spl mu/m shows larger NFmin than the 0.18-/spl mu/m case at the same finger number. From the analysis of a well-calibrated device model, the abnormal finger number dependence is due to the combined effect of reducing gate resistance and increasing substrate loss as increasing finger number. The scaling to 0.13-/spl mu/m MOSFET gives higher NF/sub min/ due to the higher gate resistance and a modified T-gate structure proposed to optimize the NF/sub min/ for further scaling down of the MOSFET.     

Low-noise metamorphic HEMTs with reflowed 0.1-/spl mu/m T-gate

A 0.1-/spl mu/m T-gate fabricated using e-beam lithography and thermally reflow process was developed and applied to the manufacture of the low-noise metamorphic high electron-mobility transistors (MHEMTs). The T-gate developed using the thermally reflowed e-beam resist technique had a gate length of 0.1 /spl mu/m and compatible with the MHEMT fabrication process. The MHEMT manufactured demonstrates a cutoff frequency f/sub T/ of 154 GHz and a maximum frequency f/sub max/ of 300 GHz. The noise figure for the 160 /spl mu/m gate-width device is less than 1 dB and the associated gain is up to 14 dB at 18 GHz. This is the first report of a 0.1 /spl mu/m MHEMT device manufactured using the reflowed e-beam resist process for T-gate formation.     

High switching performance 0.1-/spl mu/m metamorphic HEMTs for low conversion loss 94-GHz resistive mixers

We report high switching performance of 0.1-/spl mu/m metamorphic high-electron mobility transistors (HEMTs) for microwave/millimeter-wave monolithic integrated circuit (MMIC) resistive mixer applications. Very low source/drain resistances and gate capacitances, which are 56 and 31% lower than those of conventional pseudomorphic HEMTs, are due to the optimized epitaxial and device structure. Based on these high-performance metamorphic HEMTs, a 94-GHz MMIC resistive mixer was designed and fabricated, and a very low conversion loss of 8.2 dB at a local oscillator power of 7 dBm was obtained. This is the best performing W-band resistive field-effect transistor mixer in terms of conversion loss utilizing GaAs-based HEMTs reported to date.     

High performance quantum dot lasers on GaAs substrates operating in 1.5 /spl mu/m range

Stacked InAs/InGaAs quantum dots are used as an active media of metamorphic InGaAs-InGaAlAs lasers grown on GaAs substrates by molecular beam epitaxy. High quantum efficiency (/spl eta//sub i/>60%) and low internal losses (/spl alpha/<3-4 cm/sup -1/) are realised. The transparency current density per single QD layer is estimated as /spl sim/70 A/cm/sup 2/ and the characteristic temperature is 60 K (20-85/spl deg/C). The emission wavelength exceeds 1.51 /spl mu/m at temperatures above 60/spl deg/C.     

Stress-related hydrogen degradation of 0.1-/spl mu/m InP HEMTs and GaAs PHEMTs

Hydrogen degradation of III-V field-effect transistors (FETs) is a serious reliability concern. Previous work has shown that threshold-voltage shifts induced by H/sub 2/ exposure in 1-/spl mu/m-channel InP high-electron mobility transitors (HEMTs) can be attributed to compressive stress in the gate due to the formation of TiH/sub x/ in Ti/Pt/Au gates. The compressive stress affects the device characteristics through the piezoelectric effect. This paper examined the H/sub 2/ sensitivity of 0.1-/spl mu/m strained-channel InP HEMTs and GaAs pseudomorphic HEMTs. After exposure to H/sub 2/, the threshold voltage V/sub T/ of both types of devices shifted positive. This positive shift in V/sub T/ is predicted by a model for hydrogen-induced piezoelectric effect. In situ V/sub T/ measurements reveal distinct time dependences of the V/sub T/ shifts, which are also consistent with stress-related phenomena.     

High performance 1.28 /spl mu/m GaInNAs double quantum well lasers

The use of multiple quantum wells and GaAs barriers favours the temperature stability and modulation bandwidth of GaInNAs lasers. It is shown that a very low threshold current density and a high characteristic temperature can be achieved for GaInNAs/GaAs double quantum well lasers, emitting at 1.28 /spl mu/m, when grown by molecular beam epitaxy under favourable conditions.     

Microwave noise performance of AlGaN-GaN HEMTs with small DC power dissipation

We report low microwave noise performance of discrete AlGaN-GaN HEMTs at DC power dissipation comparable to that of GaAs-based low-noise FETs. At 1-V source-drain (SD) bias and DC power dissipation of 97 mW/mm, minimum noise figures (NF/sub min/) of 0.75 dB at 10 GHz and 1.5 dB at 20 GHz were achieved, respectively. A device breakdown voltage of 40 V was observed. Both the low microwave noise performance at small DC power level and high breakdown voltage was obtained with a shorter SD spacing of 1.5 /spl mu/m in 0.15-/spl mu/m gate length GaN HEMTs. By comparison, NF/sub min/ with 2 /spl mu/m SD spacing was 0.2 dB greater at 10 GHz.     

Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 /spl mu/m

A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-/spl mu/m light by Er/sup 3+/ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10/sup -3/ can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 /spl mu/m.     

Strongly sub-Poissonian electrical noise in 1.55-/spl mu/m DBR tunable laser diodes

We report terminal electrical noise measurements on 1.55-/spl mu/m DBR tunable laser diodes in the 1 Hz-1 MHz frequency range, performed using an electrical correlation method. These measurements are compared with a comprehensive electrical model based on rate equation formalism. Taking into account diffusion phenomenon and structural parameters, we obtain a complete agreement between the model and the measurements above threshold and a quite similar tendency below threshold. The influence of Bragg section bias is also discussed.     

1.27 /spl mu/m metamorphic InGaAs quantum well lasers on GaAs substrates

Pulsed operation at a wavelength of 1.27 /spl mu/m from metamorphic ridge-waveguide (RWG) InGaAs quantum well lasers on GaAs substrates using an alloy graded buffer, grown by molecular beam epitaxy, is demonstrated. Laser performance is anisotropic along the two orthogonal <1/spl plusmn/10> directions with lower threshold currents along the <1-10> direction. Post-growth rapid thermal annealing further reduces threshold currents. For 4 /spl mu/m-wide RWG lasers, minimum threshold current densities are 1-2.5 kA/cm/sup 2/ for cavity lengths 0.6-1.5 mm.     

Electroabsorption waveguide modulators at 1.3 /spl mu/m fabricated on GaAs substrates

An InGaAs-InAlAs multiple-quantum-well (MQW) electroabsorption (EA) waveguide modulator fabricated on a GaAs substrate has been designed and characterized at 1.3-/spl mu/m wavelength for microwave signal transmission on an analog fibre-optic link. The modulator structure with a lattice constant 2.5% larger than that of GaAs is grown upon a 0.7-/spl mu/m-thick three-stage compositionally step-graded In/sub z/Al/sub 1-z/As relaxed buffer. The waveguide modulator exhibits a high-electrooptic slope efficiency of 0.56 V/sup -1/, a 3-dB electrical bandwidth of 20 GHz, and a large optical saturation intensity in excess of 17 mW. These high-speed optoelectronic modulators could potentially be integrated with on-chip GaAs electronic driver circuits.     

A miniature Q-band low noise amplifier using 0.13-/spl mu/m CMOS technology

A miniature Q-band low noise amplifier (LNA) using 0.13-/spl mu/m standard mixed signal/radio frequency complementary metal-oxide-semiconductor (CMOS) technology is presented in this letter. This three-stage common source thin-film microstrip LNA achieves a peak gain of 20dB at 43GHz with a compact chip size of 0.525mm/sup 2/. The 3-dB frequency bandwidth ranges from 34 to 44GHz and the minimum noise figure is 6.3dB at 41GHz. The LNA outperforms all the reported commercial standard CMOS Q-band LNAs, with the highest gain, highest output IP3, and smallest chip size.     

1.31-1.55-/spl mu/m phased-array demultiplexer on InP

The first demultiplexers on InP at 1.31-1.55 /spl mu/m based on low-order waveguide arrays have been fabricated and characterized. We show the calculated and measured spectral responses of two devices with 6 and 10 waveguides in the grating. The on-chip loss of the devices is 4.5 dB and the crosstalks are down to -25 dB. Thanks to their large bandwidth, the devices are polarization insensitive and no strong influence of the temperature is seen.     

12 W/mm AlGaN-GaN HFETs on silicon substrates

Al/sub 0.26/Ga/sub 0.74/N-GaN heterojunction field-effect transistors were grown by metal-organic chemical vapor deposition on high-resistivity 100-mm Si (111) substrates. Van der Pauw sheet resistance of the two-dimensional electron gas was 300 /spl Omega//square with a standard deviation of 10 /spl Omega//square. Maximum drain current density of /spl sim/1 A/mm was achieved with a three-terminal breakdown voltage of /spl sim/200 V. The cutoff frequency and maximum frequency of oscillation were 18 and 31 GHz, respectively, for 0.7-/spl mu/m gate-length devices. When biased at 50 V, a 2.14-GHz continuous wave power density of 12 W/mm was achieved with associated large-signal gain of 15.3 dB and a power-added efficiency of 52.7%. This is the highest power density ever reported from a GaN-based device grown on a silicon substrate, and is competitive with the best results obtained from conventional device designs on any substrate.     

Enhanced-performance of AlGaN-GaN HEMTs grown on grooved sapphire substrates

We report significantly improved dc characteristics and RF performance of AlGaN-GaN HEMTs grown on grooved sapphire substrates. Grooves 60 nm deep with 2-/spl mu/m-wide ridges and 4-/spl mu/m-wide trenches were created along the <101~0> orientation of the substrate by inductively coupled-plasma reactive ion etching. Device mesas were defined over the trench regions where superior crystalline quality was observed by other characterization techniques. Compared to conventional HEMTs grown on the planar area, the devices on the grooved substrate show increased drain saturation current and peak transconductance. Their reverse gate leakage current is over three orders of magnitude lower. These devices also show increased off-state breakdown voltage with hard breakdown characteristics. For nominal 1-/spl mu/m-gate-length HEMTs, the best current gain and power gain cutoff frequencies were 15 and 54 GHz, respectively. The on-wafer output power, gain, and power-added efficiency of an unpassivated device measured at 4 GHz were 3.26 W/mm, 25.7 dB, and 55.6%. The enhanced performance is attributed to low-density mixed dislocations and high crystalline quality over the trench regions.     

Photonic-crystal surface-emitting laser near 1.55 /spl mu/m on gold-coated silicon wafer

An InP/InGaAs-based photonic band-edge laser bonded on silicon operating near 1.55 mum is presented. A gold reflector positioned below the slab containing the active layer reduces the optical losses of the Bloch-mode resonator. As a result, a quality factor exceeding 8000 is obtained at transparency leading to a laser threshold as low as 3.4 muJ/cm²     

Improved high-temperature performance of 1.3-1.5-/spl mu/m InNAsP-InGaAsP quantum-well microdisk lasers

We report for the first time lasing action in the InNAsP-InGaAsP material system. Dramatic improvement in lasing action in a microdisk cavity was observed at elevated temperature up to 70/spl deg/C, which is about 120/spl deg/C higher than that of InGaAs-InGaAsP microdisk. This resulted in the first optically pumped InNAsP-InGaAsP microdisk lasers capable of above room-temperature lasing. The improvement of lasing temperature can be attributed to a large conduction band offset between the quantum well and barriers in the InNAsP-InGaAsP material system.     

9.4-W/mm power density AlGaN-GaN HEMTs on free-standing GaN substrates

High power microwave AlGaN-GaN high electron-mobility transistors (HEMTs) on free-standing GaN substrates are demonstrated for the first time. Measured gate leakage was -2.2 /spl mu/A/mm at -20 V and -10 /spl mu/A/mm at -45 V gate bias. When operated at a drain bias of 50 V, devices showed a record continuous-wave output power density of 9.4 W/mm at 10 GHz with an associated power-added efficiency of 40%. Long-term stability of device RF operation was also examined. Under room conditions, devices driven at 25 V and 3-dB gain compression remained stable in 200 h, degrading only by 0.18 dB in output power. Such results illustrate the potential of GaN substrate technology in supporting reliable, high performance AlGaN-GaN HEMTs for microwave power applications.