An AlGaN/GaN two-color photodetector based on AlGaN/GaN/SiC HEMT layer structure

in Physica Status Solidi C. Current Topics in Solid State Physics (2006), 3(6), 2261-2264

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a ... [more ▼]

The optoelectronic properties of MSM diodes that are based on an AlGaN/GaN HEMT layer system are investigated as function of the applied bias. For low voltages, the two-dimensional electron gas acts as a barrier for the depletion layer. Therefore, only the upper AlGaN barrier layer contributes to the photocurrent. In the high voltage regime the depletion region penetrates the GaN buffer that adds the spectral responsivity of GaN to the pure AlGaN behaviour in the low voltage regime. The ratio of the responsivities at 350 nm and 300 nm wavelength can be switched from 0.01 at 2.5 V to 0.8 at 4 V bias. This property makes the MSM-2DEG a candidate for use as two-color photodetector. Device fabrication uses standard HEMT processing steps, allowing integration in HEMT circuits without the need of sophisticated growth or etching techniques. [less ▲]

Comparative study on unpassivated and passivated AlGaN/GaN HFETs and MOSHFETs

in Physica Status Solidi A. Applications and Materials Science (2006), 203(7), 1876-1881

In this comparative study we investigate AlGaN/GaN-based unpassivated and passivated HFETs and MOSHFETs with regards to DC-, RF-, and power-performance. For optimal comparability, all devices emanate from ... [more ▼]

In this comparative study we investigate AlGaN/GaN-based unpassivated and passivated HFETs and MOSHFETs with regards to DC-, RF-, and power-performance. For optimal comparability, all devices emanate from the same wafer consisting of a SiC-substrate, a 3 μm GaN- and a 30 nm Al0.28Ga0.72N-layer. Devices are processed simultaneously to a large extend. Passivated devices are coated with a 10 nm thick SiO2-layer between the electrodes, MOSHFETs contain a 10 nm thick SiO2-layer serving as gate-insulator underneath the gate and as conventional passivation-layer between the electrodes. Unpassivated devices serve as reference. We present empirical evidence that MOSHFETs outperform both the conventional and the passivated HFETs with respect to DC-, RF-, and power-performance, and we point out the different mechanisms responsible for the behaviour of the devices. [less ▲]

Comparison of AlGaN/GaN MSM Varactor Diodes Based on HFET and MOSHFET Layer Structures

in IEEE Electron Device Letters (2006), 27

In this letter, the performance of AlGaN/GaN-based metal–semiconductor–metal (MSM) varactor diodes based on HFET and MOSHFET layer systems is investigated. Passivated HFET MSM devices are coated with a 10 ... [more ▼]

In this letter, the performance of AlGaN/GaN-based metal–semiconductor–metal (MSM) varactor diodes based on HFET and MOSHFET layer systems is investigated. Passivated HFET MSM devices are coated with a 10-nm-thick SiO2 layer between the electrodes; in MOSHFET-based diodes, this layer is also used as an insulator underneath the gate. Device fabrication uses standard HFET fabrication technology, allowing easy integration in monolithic microwave integrated circuits. Devices with different electrode geometry are characterized by direct current and by S-parameter measurements up to 50 GHz. The HFET-based varactors show capacitance ratios up to 14 and cutoff frequencies up to 74 GHz. The MOSHFET-based devices, on the other hand, show lower capacitance ratios and poorer stability because of the insulation layer between electrodes and semiconductor. [less ▲]

High-power SiO2/AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors

in Applied Physics Letters (2005), 87(14), 143501-143504

We report on SiO2 /AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors MOSHFETs , which exhibit a 6.7 W/mm power density at 7 GHz. Unpassivated and SiO2-passivated heterostructure ... [more ▼]

We report on SiO2 /AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors MOSHFETs , which exhibit a 6.7 W/mm power density at 7 GHz. Unpassivated and SiO2-passivated heterostructure field-effect transistors HFETs were also investigated for comparison. Deposited 12 nm thick SiO2 yielded an increase of the sheet carrier density from 7.6 .10^12 to 9.2 .10^12 cm−2 and a subsequent increase of the static drain saturation current from 0.75 to 1.09 A/mm. The small-signal rf characterization of the MOSHFETs showed an extrinsic current gain cutoff frequency fT of 24 GHz and a maximum frequency of oscillation fmax of 40 GHz. The output power of 6.7 W/mm of the MOSHFETs measured at 7 GHz is about two times larger than that of HFETs. The results obtained demonstrate the suitability of GaN-based MOSHFETs for high-power electronics. [less ▲]

SiO2 /AlGaN/GaN MOSHFET with 0.7 µm gate-length and fmax / fT of 40/24 GHz

in Electronics Letters (2005), 41(11), 667-668

The performance of SiO2/AlGaN/GaN MOSHFETs is described. The C–V measurements showed slight increase in sheet carrier density after applying 12 nm-thick PECVD SiO2. The devices exhibited gate leakage ... [more ▼]

The performance of SiO2/AlGaN/GaN MOSHFETs is described. The C–V measurements showed slight increase in sheet carrier density after applying 12 nm-thick PECVD SiO2. The devices exhibited gate leakage current of 5 .10 ^-10 A/mm. Small-signal RF characterisation of 0.7 mm gate length devices yielded an fT of 24 GHz and an fmax of 40 GHz, which are comparable to those typical for state-of-the-art AlGaN/GaN HFETs. [less ▲]

Performance of unpassivated AlGaN/GaN/SiC HEMTs after short-term electrical bias stress

in Solid-State Electronics (2004), 48((2004)), 1825-1828

Performance of unpassivated MOVPE grown AlGaN/GaN/SiC HEMTs under short-term electrical bias stress isreported. Insignificant degradation in DC and RF behaviour of prepared devices after 16 h stress at VD ... [more ▼]

Performance of unpassivated MOVPE grown AlGaN/GaN/SiC HEMTs under short-term electrical bias stress isreported. Insignificant degradation in DC and RF behaviour of prepared devices after 16 h stress at VD ¼ 21 V and VG ¼ 2:5 V is observed. This can be demonstrated by a maximum drain current of 1.03 and 1.01 A/mm and a peak extrinsic transconductance of 233 and 225 mS/mm before and after bias stress, respectively. Consecutive drain voltage sweeps indicates on low current collapse in samples investigated. The RF characteristics show a decrease of the fmax-tof T ratio from 2.23 to 2.15 and the saturated output power density measured at 2 GHz from 3.60 to 3.53 W/mm after the devices were stressed. This result indicates that reliable AlGaN/GaN/SiC HEMTs without passivation can be prepared. However, additional studies are needed to understand if the material structure and/or the device processing is responsible for low current collapse and RF dispersion in these devices. [less ▲]

DC and Pulsed Behaviour of Undoped and Doped AlGaN/GaN/SiC HEMTs before and after Si3N4 passivation

in Proc. 5th Intern. Conf. Advanced Semicon. Dev. & Microsystems ASDAM’04 (2004)

Influence of layer structure on performance of AlGaN/GaN High Electron Mobility Transistors before and after passivation

in Journal of Electronic Materials (2004), 33((2004)), 436-439

Effect of surface passivation on performance of AlGaN/GaN/Si HEMTs

in Solid-State Electronics (2003), 47((2003)), 2097-2103

Performance of intentionally undoped and doped AlGaN/GaN/Si high electron mobility transistors (HEMTs) before and after passivation with SiO2 and Si3N4 is investigated. Hall effect measurements show ... [more ▼]

Performance of intentionally undoped and doped AlGaN/GaN/Si high electron mobility transistors (HEMTs) before and after passivation with SiO2 and Si3N4 is investigated. Hall effect measurements show higher impact of Si3N4 than SiO2 passivation on the carrier concentration increase in the channel. Improvements in DC performance of HEMTs after passivation with SiO2 and Si3N4 correspond to the changes in sheet carrier concentration. Small signal microwave characterisation shows a decrease (from 18.6 to 9 GHz) and an increase (from 18.4 to 28.8 GHz) of the current gain cut off frequency after SiO2 and Si3N4 passivation, respectively. Similar effect of passivation is found in microwave power changes––only about a half of the power is obtained after SiO2 passivation but more than doubled power results from Si3N4 passivation, measured at 2 GHz. Higher density of interface states for SiO2 than Si3N4 passivation is supposed to be responsible for these effects. However, for an optimal design of GaN-based power devices additional studies related to the interface between a passivation layer and GaN are needed. [less ▲]

Influence of doping concentration on DC and RF performance of AlGaN/GaN HEMTs on silicon substrate

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 ▲]