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See detailBackgating high-current and breakdown characterisation of AlGaN/GaN HEMTs on silicon substrates
Kuzmik, J.; Blaho, M.; Pogany, D. et al

in Proceedings of the ESSDERC 2003. Estoril, Portugal (2003)

Backgating effect as well as breakdown and high-current performance of AlGaN/GaN HEMTs on silicon substrates are studied. The material structure of investigated devices differ in the thickness of ... [more ▼]

Backgating effect as well as breakdown and high-current performance of AlGaN/GaN HEMTs on silicon substrates are studied. The material structure of investigated devices differ in the thickness of stressrelaxing intermediate layer sequence (~1 μm and ~2.5 μm thick). It is shown that the transistor backgating effect is reduced for the thicker sequence. Similarly, the reverse gate current is two orders of the magnitude lower and the gate-drain breakdown voltage increases substantially in devices with the thicker sequence. Increase from ~40 V to ~160 V of the HEMT blocking capability measured under electrostatic discharge-like conditions is also observed. [less ▲]

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See detailMaterial and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates
Javorka, P.; Alam, A.; Marso, Michel UL et al

in Microelectronics Journal (2003), 34

Selected material and device issues related to the performance of AlGaN/GaN HEMTs on (111) Si substrates are reported. It is shown that these devices can sustain significantly higher dc power (16 W/mm ... [more ▼]

Selected material and device issues related to the performance of AlGaN/GaN HEMTs on (111) Si substrates are reported. It is shown that these devices can sustain significantly higher dc power (16 W/mm) than those grown on sapphire. Consequently smaller degradation in the device performance at higher temperatures (up to 400 8C) is demonstrated. Photoionisation spectroscopy reveals trap level of 1.85 eV, additional to two another levels found before in GaN-based HEMTs prepared on sapphire. Thus, AlGaN/GaN HEMTs on Si substrates demonstrate the viability of this technology for commercial application of high power rf devices. [less ▲]

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See detailInfluence of doping concentration on DC and RF performance of AlGaN/GaN HEMTs on silicon substrate
Marso, Michel UL; Javorka, P.; Dikme, Y. et al

in Physica Status Solidi A. Applications and Materials Science (2003), (1), 179-182

AlGaN/GaN HEMTs with different carrier supply layers are fabricated on Si substrate, using MOVPE growth technique. The influence of the carrier supply doping concentration on the HEMT properties is ... [more ▼]

AlGaN/GaN HEMTs with different carrier supply layers are fabricated on Si substrate, using MOVPE growth technique. The influence of the carrier supply doping concentration on the HEMT properties is investigated by Hall measurements and by electrical DC and RF characterisation of transistor devices. Hall mobility is found to decrease with increasing sheet concentration, while the gate leakage current increases. The device with the highest carrier supply doping concentration of 1019 cm–3 is provided with a GaN cap layer to reduce gate leakage. The transistors based on modulation doped layer structures show much higher DC performance than the undoped device. Best RF properties are obtained for a doping level of 5 × 1018 cm–3. High frequency measurements exhibit fT and fMAX values of 35 GHz and 37 GHz, respectively, for devices with 300 nm gate length. [less ▲]

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See detailMaterial and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates
Javorka, P.; Alam, A.; Marso, Michel UL et al

in Proceedings of the MRS Fall Meeting, Boston 2002 (2003)

Results on the preparation and properties of AlGaN/GaN HEMTs on silicon substrates are presented and selected issues related to the material structure and device performance devices are discussed ... [more ▼]

Results on the preparation and properties of AlGaN/GaN HEMTs on silicon substrates are presented and selected issues related to the material structure and device performance devices are discussed. Virtually crack-free AlGaN/GaN heterostructures (xAlN ≅ 0.25), with low surface roughness (rms of 0.64 nm), ns ≅ 1×1013 cm-2 and μ ≅ 1100 cm2/V s at 300 K, were grown by LP-MOVPE on 2-inch (111)Si substrates. HEMT devices with Lg = 0.3−0.7 μm were prepared by conventional device processing steps. Photoionization spectroscopy measurements have shown that a trap level of 1.85 eV, additional to two levels of 2.9 and 3.2 eV found before on GaN-based HEMTs on sapphire, is present in the structures investigated. Self-heating effects were studied by means of temperature dependent dc measurements. The channel temperature of a HEMT on Si increases with dissipated power much slower than for similar devices on sapphire substrate (e.g. reaches 95 and 320 °C on Si and sapphire, respectively, for 6 W/mm power). Prepared AlGaN/GaN/Si HEMTs exhibit saturation currents up to 0.91 A/mm, a good pinch-off, peak extrinsic transconductances up to 150 mS/mm and static heat dissipation capability up to ~16 W/mm. Unity current gain frequencies fT up to 21 and 32 GHz were obtained on devices with gate length of 0.7 and 0.5 μm, respectively. The saturation current and fT values are comparable to those known for similar devices using sapphire and SiC substrates. Properties of AlGaN/GaN/Si HEMTs investigated show that this technology brings a prospect for commercial application of high power rf devices. [less ▲]

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See detailGrowth and characterisation of AlGaN/GaN-HEMTs on silicon substrates,
Kalisch, H.; Dikme, Y.; Gerstenbrandt, G. et al

in Physica Status Solidi A. Applications and Materials Science (2002), 194(2), 464-467

In order to analyse and to compare the properties of AlGaN/GaN HEMT on silicon and on sapphire substrates, studies on both layers and device types have been performed. Besides the substantially lower ... [more ▼]

In order to analyse and to compare the properties of AlGaN/GaN HEMT on silicon and on sapphire substrates, studies on both layers and device types have been performed. Besides the substantially lower substrate costs compared to SiC, the use of silicon as substrate provides the advantage of a higher thermal conductivity compared to sapphire allowing a more efficient heat removal from the device and thus higher RF power densities. On silicon, up to 900 nm of GaN as well as HEMT structures have been deposited and characterised regarding their structural, optical and electrical properties. HEMT devices with various gate lengths were processed and measured onwafer under continuous and pulsed operation conditions. The properties of the layers and devices on silicon substrates are developing to become comparable to those based on sapphire and silicon carbide. [less ▲]

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See detailInvestigation of AlGaN/GaN HEMTs on Si substrate using backgating
Marso, Michel UL; Wolter, M.; Javorka, P. et al

in Physica Status Solidi C. Current Topics in Solid State Physics (2002), (1), 65-68

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN HEMT on silicon (111) substrate is investigated. This effect, known as backgating, is used to study traps that are located ... [more ▼]

The influence of a substrate voltage on the dc characteristics of an AlGaN/GaN HEMT on silicon (111) substrate is investigated. This effect, known as backgating, is used to study traps that are located between substrate and 2DEG channel. The transient of the drain current after applying a negative substrate voltage is evaluated for measurements with and without illumination. Several trap contributions are resolved by measurements at different photon energies. A photocurrent is observed up to 600 nm wavelength. Up to this wavelength the backgating effect can be compensated and the drain current restored by a short light pulse. The experiments are performed on completed HEMTs, allowing investigation of the influence of device fabrication technology. [less ▲]

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See detailHigh-performance AlGaN/GaN HEMTs on silicon substrates
Javorka, P.; Alam, A.; Fox, A. et al

in Proc. 4th Intern. Conf. Advanced Semicon. Dev. & Microsystems (2002)

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See detailMaterial and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates
Javorka, P.; Alam, A.; Marso, Michel UL et al

in Mat. Res. Soc. Symp. Proc. Vol. 743 (2002), 743, L9.1.1

Results on the preparation and properties of AlGaN/GaN HEMTs on silicon substrates are presented and selected issues related to the material structure and device performance devices are discussed ... [more ▼]

Results on the preparation and properties of AlGaN/GaN HEMTs on silicon substrates are presented and selected issues related to the material structure and device performance devices are discussed. Virtually crack-free AlGaN/GaN heterostructures (xAlN ≅ 0.25), with low surface roughness (rms of 0.64 nm), ns ≅ 1×1013 cm-2 and μ ≅ 1100 cm2/V s at 300 K, were grown by LP-MOVPE on 2-inch (111)Si substrates. HEMT devices with Lg = 0.3−0.7 μm were prepared by conventional device processing steps. Photoionization spectroscopy measurements have shown that a trap level of 1.85 eV, additional to two levels of 2.9 and 3.2 eV found before on GaN-based HEMTs on sapphire, is present in the structures investigated. Self-heating effects were studied by means of temperature dependent dc measurements. The channel temperature of a HEMT on Si increases with dissipated power much slower than for similar devices on sapphire substrate (e.g. reaches 95 and 320 °C on Si and sapphire, respectively, for 6 W/mm power). Prepared AlGaN/GaN/Si HEMTs exhibit saturation currents up to 0.91 A/mm, a good pinch-off, peak extrinsic transconductances up to 150 mS/mm and static heat dissipation capability up to ~16 W/mm. Unity current gain frequencies fT up to 21 and 32 GHz were obtained on devices with gate length of 0.7 and 0.5 μm, respectively. The saturation current and fT values are comparable to those known for similar devices using sapphire and SiC substrates. Properties of AlGaN/GaN/Si HEMTs investigated show that this technology brings a prospect for commercial application of high power rf devices. [less ▲]

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See detailDetermination of channel temperature in AlGaN/GaN HEMTs grown on sapphire and silicon substrates using DC characterization method
Kuzmík, J.; Javorka, P.; Alam, A. et al

in IEEE Transactions on Electron Devices (2002), 49(8), 1496-1498

Self-heating effects and temperature rise in AlGaN/GaN HEMTs grown on silicon and sapphire substrates are studied, exploiting transistor dc characterization methods. A negative differential output ... [more ▼]

Self-heating effects and temperature rise in AlGaN/GaN HEMTs grown on silicon and sapphire substrates are studied, exploiting transistor dc characterization methods. A negative differential output resistance is observed for high dissipated power levels. An analytical formula for a source-drain current drop as a function of parasitic source resistance and threshold voltage changes is proposed to explain this behavior. The transistor source resistance and threshold voltage is determined experimentally at different elevated temperatures to construct channel temperature versus dissipated power transfer characteristic. It is found that the HEMT channel temperature increases rapidly with dissipated power and at 6 W/mm reaches values of 320 C for sapphire and 95 C for silicon substrate, respectively. [less ▲]

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See detailFabrication and performance of AlGaN/GaN HEMTs on (111) Si substrates
Javorka, P.; Alam, A.; Marso, Michel UL et al

in Physica Status Solidi A. Applications and Materials Science (2002), 194(2), 472-475

In the current work the performance of AlGaN/GaN HEMTs fabricated on silicon substrates is presented. The AlGaN/GaN material structures were grown on (111) Si by MOVPE. Static I–V characteristics with a ... [more ▼]

In the current work the performance of AlGaN/GaN HEMTs fabricated on silicon substrates is presented. The AlGaN/GaN material structures were grown on (111) Si by MOVPE. Static I–V characteristics with a saturation current of 0.91 A/mm and a peak extrinsic transconductance of 122 mS/mm were measured and show minimal thermal effects. For devices with a gate length of 0.7 um and 0.5 um, a unity gain frequency of 20 GHz and 32 GHz and a maximum frequency of oscillation of 22 GHz and 27 GHz, respectively were obtained. The unity gain frequencies are the highest values reported so far on AlGaN/GaN/Si HEMTs and fully comparable to those known for devices using sapphire and SiC substrates. However, the fmax to fT ratio is only about 1, which indicates on parasitic conduction through the Si substrate under small signal conditions. It is shown that the saturation current and the transconductance decrease much less with increased temperature than known for similar devices grown on sapphire. [less ▲]

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See detailPhotoionization spectroscopy of traps in doped and undoped AlGaN/GaN HEMTs
Wolter, M.; Javorka, P.; Marso, Michel UL et al

in Physica Status Solidi C. Current Topics in Solid State Physics (2002), (1), 82-85

Deep-level defects and surface states are supposed to be responsible for the limitation of AlGaN/GaN high electron mobility transistor (HEMT) performance. In order to investigate the influence of these ... [more ▼]

Deep-level defects and surface states are supposed to be responsible for the limitation of AlGaN/GaN high electron mobility transistor (HEMT) performance. In order to investigate the influence of these traps, photoionization spectroscopy was used to study doped and undoped HEMTs grown on sapphire in different metalorganic vapour-phase epitaxy reactors. This measurement technique is based on the optical reversion of the current collapse and it allows one to determine photoionization cross-sections of the participating traps. For doped and undoped HEMTs nearly the same two defect levels with excitation energies of 3.2 eV and 2.9 eV were determined. By varying the source–gate voltage it was found that the photoionization cross-section is reduced for positive gate bias, i.e. the virtual gate on the gate–drain access region is partially neutralized due to the removal of trapped electrons from surface states. [less ▲]

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See detailAlGaN/GaN HEMTs on (111) Silicon Substrates
Javorka, P.; Alam, A.; Wolter, M. et al

in IEEE Electron Device Letters (2002), 23(2002), 4-6

AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE ... [more ▼]

AlGaN/GaN HEMTs on silicon substrates have been fabricated and their static and small-signal RF characteristics investigated. The AlGaN/GaN material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current of 0.91 A/mm, a good pinchoff and a peak extrinsic transconductance of 122 mS/mm. A unity current gain frequency of 12.5 GHz and fmax/fT=0.83 were obtained. The highest saturation current reported so far, static output characteristics of up to 20 V and breakdown voltage at pinchoff higher than 40 V demonstrate that the devices are capable of handling 16 W/mm static heat dissipation. [less ▲]

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See detailAlGaN/GaN HEMTs on Silicon Substrates with f¬T of 32/20 GHz and fmax of 27/22 GHz for 0.5/0.7 µm gate length,
Javorka, P.; Alam, A.; Fox, A. et al

in Electronics Letters (2002), 38(2002), 288-289

AlGaN/GaN HEMTs on silicon substrates have been realised and their static and small signal characteristics investigated. The AlGaN/GaN (x=0.23) material structures were grown on (111) p-Si by LP-MOVPE ... [more ▼]

AlGaN/GaN HEMTs on silicon substrates have been realised and their static and small signal characteristics investigated. The AlGaN/GaN (x=0.23) material structures were grown on (111) p-Si by LP-MOVPE. Devices exhibit a saturation current density of 0.53 to 0.68 A/mm and a peak extrinsic transconductance of 110 mS/mm. A unity gain frequency of 20 and 32 GHz and a maximum frequency of oscillation of 22 and 27 GHz are obtained for devices with a gate length of 0.7 and 0.5 mm, respectively. These values are the highest reported so far on AlGaN=GaN=Si HEMTs and are comparable to those known for devices using sapphire and SiC substrates. [less ▲]

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See detailOptimization of AlGaN/GaN HEMT performance
Javorka, P.; Wolter, M.; Alam, A. et al

in Proc. EDMO (2001)

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See detailInvestigations on the influence of traps in AlGaN/GaN HEMTs
Wolter, M.; Javorka, P.; Marso, Michel UL et al

in EDMO (2001)

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See detailAlGaN/GaN Round-HEMTs on (111) silicon substrates
Javorka, P.; Alam, A.; Nastase, N. et al

in Electronics Letters (2001), 37(2001), 1364-1366

AlGaN/GaN Round-HEMTs on silicon substrates have been realised and their static characteristics investigated. The AlGaN/GaN (x = 0.23) material structures were grown on (111) p-Si by LP-MOVPE. Devices ... [more ▼]

AlGaN/GaN Round-HEMTs on silicon substrates have been realised and their static characteristics investigated. The AlGaN/GaN (x = 0.23) material structures were grown on (111) p-Si by LP-MOVPE. Devices with 0.3 mm gate length exhibit a saturation current of 0.82 A/mm, a good pinch-off and a peak extrinsic transconductance of 110 mS/mm. Highest saturation current reported so far and static output characteristics up to 20 V demonstrate that the devices are capable of handling 16 W/mm of static heat dissipation without any degradation of their performance. [less ▲]

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See detailAlGaN/GaN HEMT Optimization Using the RoundHEMT Technology
Marso, Michel UL; Javorka, P.; Alam, A. et al

in Physica Status Solidi A. Applied Research (2001), 188

The electrical characterization of epitaxially grown HEMT layer systems for device fabrication is commonly performed by Hall measurements. However, the ultimate characterization of a HEMT layer system is ... [more ▼]

The electrical characterization of epitaxially grown HEMT layer systems for device fabrication is commonly performed by Hall measurements. However, the ultimate characterization of a HEMT layer system is the transistor device itself. The RoundHEMT concept meets the need for a device technology with few fabrication steps that allows a fast feedback to epitaxy while providing an evaluation of important electrical and also processing data. Even though nearly identical Hall data on structures with different thickness and doping concentration of the AlGaN layers suggest similar device properties, the RoundHEMTs resolve remarkable differences in device performance. The best layer structure was used to fabricate HEMTs with IDS = 700 mA/mm, fT = 35 GHz, and fmax = 70 GHz for LG = 0.2 mm. [less ▲]

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See detailInvestigation of self-heating effects in AlGaN/GaN HEMTs
Kuzmík, J.; Javorka, P.; Alam, A. et al

in Proc. EDMO (2001)

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See detailMaterial and Device Issues of GaN-based HEMTs
Kordoš, P.; Alam, A.; Betko, J. et al

in Proceedings of the 8th International Symposium on High Performance Electron Devices for Microwave and Optoelectronic Applications (EDMO), (2000)

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