Lee Mohnkern

Gate-Length Scaling of Ultrashort Metamorphic High-Electron Mobility Transistors With Asymmetrically Recessed Gate Contacts for Millimeter- and Submillimeter-Wave Applications

We have fabricated and characterized ultrashort gate-length metamorphic high-electron mobility transistors (HEMTs) optimized for high gain performance for millimeter- and submillimeter-wave applications. In this paper, we have systematically evaluated the impact of gate length in the range of 25-50 nm on the device performance by exploring epitaxial layer designs, gate-to-channel distances, and recess widths. The study shows the 25-nm devices underperform their 50-nm counterparts in most of the key figures of merit including output conductance, voltage gain, off-state breakdown, on-state breakdown, and, most importantly, the maximum stable gain. This observation is actually in good agreement with the state-of-the-art results published so far, which indicate that the best overall performance of HEMTs for millimeter- and submillimeter-wave applications comes from devices with gate lengths ranging from 35 to 50 nm. The 25-nm devices, on the other hand, appear to have difficulty in achieving the proper vertical scaling for optimum gain, which is limited by the minimum gate layer thickness necessary to retain good Schottky characteristics. This limitation may eventually be overcome with the adoption of new materials used as the gate layer that can be integrated into the HEMT fabrication process.

50-nm Metamorphic High-Electron-Mobility Transistors With High Gain and High Breakdown Voltages

We report the design, fabrication, and characterization of ultrahigh-gain metamorphic high-electron-mobility transistors (MHEMTs) with significantly enhanced breakdown performance. In this letter, an asymmetrically recessed 50-nm Gamma-gate process has been successfully applied to epitaxial designs with double-sided-doped InAs-layer-inserted channels grown on GaAs substrates. The critical gate recess width has been optimized for device performance, including transconductance, breakdown voltage, and gain. The employment of a device passivation process greatly minimizes the adverse impacts that the aggressive vertical and lateral scaling would have introduced for pursuing enhanced performance. As a result, we have achieved 1.9-S/mm transconductance and 800-mA/mm maximum drain current at a drain bias of 1 V, 9-V off-state breakdown voltage, approximately 3.5-V on-state breakdown voltage, and 14.2-dB maximum stable gain at 110 GHz. To our knowledge, this is a record combination of gain and breakdown performance reported for microwave and millimeter-wave HEMTs, making these devices excellent candidates for ultrahigh-frequency power applications.

Asymmetrically Recessed 50-nm Gate-Length Metamorphic High Electron-Mobility Transistor With Enhanced Gain Performance

We report the design, fabrication and characterization of ultrahigh gain metamorphic high electron-mobility transistors. In this letter, a high-yield 50-nm T-gate process was successfully developed and applied to epitaxial layers containing high indium mole fraction InGaAs channels grown on GaAs substrates. A unique gate recess process was adopted to significantly increase device gain by effectively suppressing output conductance and feedback capacitance. Coupled with extremely small 10 mum times 25 mum via holes on substrates thinned to 1 mil, we achieved a 13.5 dB maximum stable gain (MSG) at 110 GHz for a 30-mum gate-width device. To our knowledge, this is the highest gain performance reported for microwave high electron-mobility transistor devices of similar gate periphery at this frequency, and equivalent circuit modeling indicates that this device will operate at frequencies beyond 300 GHz.

Second-harmonic generation of a tunable continuous-wave CO 2 laser in orientation-patterned GaAs

Tunable, mid-infrared radiation was obtained by frequency doubling of a continuous-wave CO(2) laser in orientation-patterned GaAs crystal. Active cooling of the crystal minimized pump-induced thermal effects, allowing generation of output powers exceeding 300 mW across the wavelength range of 4.63-4.78 μm.

Recent advances in all-epitaxial growth and properties of orientation-patterned gallium arsenide (OP-GaAs)

We report on all-epitaxial growth of large diameter (3-inch), large aperture (≫1.5mm thick), low-loss (≪0.005cm⁻¹) QPM GaAs. 2-µm-laser-pumped OPO performance was comparable to that of ZnGeP<inf>2</inf>.

50-nm Asymmetrically Recessed Metamorphic High-Electron Mobility Transistors With Reduced Source–Drain Spacing: Performance Enhancement and Tradeoffs

Whereas gate-length reduction has served as the major driving force to enhance the performance of GaAs- and InP-based high-electron mobility transistors (HEMTs) over the past three decades, the limitation of this approach begins to emerge. In this paper, we present a systematic evaluation of the impact of greatly reduced source-drain spacing on the performance of 50-nm asymmetrically recessed metamorphic HEMTs (MHEMTs). Extremely high extrinsic transconductance has been achieved over a wide drain bias range starting from as low as 0.1 V by reducing source-drain spacing to 0.5 μm with a self-aligned (SAL) ohmic process. The measured maximum extrinsic transconductance of 3 S/mm is a new record for all HEMT devices on a GaAs substrate and is equal to the best results reported for InP-based HEMTs. With the use of an asymmetric recess, SAL MHEMTs also demonstrate remarkable improvement in other major figures of merit, including off-state breakdown, on-state breakdown, subthreshold characteristics, ION/IOFF ratio, and the voltage gain over the other SAL HEMTs reported so far. However, they still, in a few respects, under perform the conventional devices typically with 2-μm source-drain spacing. In particular, the on-state breakdown of the SAL devices has been capped at approximately 2 V, even with a very wide asymmetric recess. It appears that the uniqueness of the SAL technology would best fit applications that require low voltage and/or low DC power consumption, which can be fully tapped only when the parasitic capacitance is also properly controlled with, e.g., a high stem gate process.

2.05-/spl mu/m-laser-pumped orientation-patterned gallium arsenide (OPGaAs) OPO

We achieved the highest average power (0.45 W) and efficiency (20% slope) to date from an OPGaAs OPO. QPM structures >1 mm thick were grown by HVPE on 3-inch diameter multi-grating templates produced by MBE.

Frequency doubling of a CO2 laser using orientation patterned GaAs

High efficiency second harmonic generation of a pulsed TEA CO2 laser operating at 9.569 μm was demonstrated in a quasi-phase-matched GaAs structure, 1.48 mm thick, 39.7 mm long and 8.3 mm wide, and having a grating period of 219.6 μm. The structure was grown by hydride vapor phase epitaxy and was dual-band anti-reflection coated on both entrance and exit surfaces. Energy of 1.2 mJ was obtained at 4.78 μm from single pass conversion with incident energy of 2.56 mJ.

50-NM SELF-ALIGNED HIGH ELECTRON-MOBILITY TRANSISTORS ON GaAs SUBSTRATES WITH EXTREMELY HIGH EXTRINSIC TRANSCONDUCTANCE AND HIGH GAIN

We report the design, fabrication and characterization of metamorphic high electron-mobility transistors (MHEMTs) with self-aligned ohmic electrodes. In this work, asymmetrically recessed 50-nm Γ-gates have been successfully used as the shadow mask for ohmic metal deposition. Extremely high extrinsic transconductance over a wide drain bias from 0.1 to 1.25 V can be made possible by fabricating devices with small gate-source spacing, small source-drain spacing, and the non-alloyed ohmic. Measured maximum extrinsic transconductance of 3 S/mm is a new record for all HEMT devices on GaAs and equals the best results from InP-based HEMTs. The same devices also show a voltage gain of 22, maximum stable gain of 10.8 dB at 110 GHz, and breakdown voltage of 4.3 V, which all are the highest among any self-aligned HEMTs based on InGaAs channel. The outstanding performance is the result of the seamless integration of the asymmetric gate recess and Γ-gate-based self-aligned ohmic process.

HIGH-PERFORMANCE 50-NM METAMORPHIC HIGH ELECTRON-MOBILITY TRANSISTORS WITH HIGH BREAKDOWN VOLTAGES

This paper reports a successful improvement of the low breakdown voltages in short gate-length metamorphic high electron-mobility transistors. The technical approach includes both the optimization of the epitaxial layer design and the selection of the proper gate recess scheme. By employing a novel epitaxial design (including a high indium composite channel and the double-sided doping) and an asymmetric gate recess, both the off-state and on-state breakdown voltages have been improved for 50-nm high-performance metamorphic high electron-mobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.