Wet low-temperature gate oxidation for nanoscale vertical field-effect transistors,

in Physica E: Low-Dimensional Systems and Nanostructures (2003), 19(2003), 18-22

In this work, we present an approach towards improving a vertical eld-e ect transistor based on a narrow mesa that is capable of showing complete channel inversion. Contrary to similar concepts it does ... [more ▼]

In this work, we present an approach towards improving a vertical eld-e ect transistor based on a narrow mesa that is capable of showing complete channel inversion. Contrary to similar concepts it does not necessarily require the use of an SOI substrate due to the chosen vertical layer sequence. An important issue during process flow is the limited thermal budget in order to preserve the desired channel length. Here a low-temperature wet oxidation process is investigated to prevent dopant di ffusion in early process steps. Results on the thickness homogeneity and electrical properties of this gate oxide will be presented and discussed. [less ▲]

Fabrication and performance of AlGaN/GaN HEMTs on (111) Si substrates

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 ▲]

Determination of channel temperature in AlGaN/GaN HEMTs grown on sapphire and silicon substrates using DC characterization method

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 ▲]

Thin low-temperature gate oxides for vertical field-effect transistor, ,

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

RF small-signal and power characterization of AlGaN/GaN HEMTs

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

Annealing of Schottky contacts deposited on dry etched AlGaN/GaN,

in Semiconductor Science and Technology (2002), 17((2002).), 76-78

The influence of annealing on properties of Pt Schottky contacts deposited on the electron cyclotron resonance plasma etched surface of an AlGaN/GaN heterostructure has been investigated. It is found that ... [more ▼]

The influence of annealing on properties of Pt Schottky contacts deposited on the electron cyclotron resonance plasma etched surface of an AlGaN/GaN heterostructure has been investigated. It is found that rapid thermal annealing (450 ◦C and 40 s in nitrogen gas), performed after metal deposition, allows for the preparation of Schottky contacts with similar or better properties than those obtained on a non-etched surface. This procedure is suitable for the realization of recessed high-quality Schottky contacts of AlGaN/GaN HEMTs. [less ▲]

Material and Device Issues of AlGaN/GaN HEMTs on Silicon Substrates

in Materials Research Society Symposia Proceedings (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 ▲]

AlGaN/GaN HEMTs on (111) Silicon Substrates

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 ▲]

Investigation of AlGaN/GaN HEMTs on Si substrate using backgating

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 ▲]

Photoionization spectroscopy of traps in AlGaN/GaN HEMTs

in Journal of Electronic Materials (2002), 31(12), 1321-1324