New approaches for growth control of GaN-based HEMT structure

in Applied Physics A : Materials Science & Processing (2007), 87(3), 491-498

This paper reports on new approaches for growth control of GaN-based heterostructures for high frequency and high power application. First in situ methods are presented and their further development ... [more ▼]

This paper reports on new approaches for growth control of GaN-based heterostructures for high frequency and high power application. First in situ methods are presented and their further development discussed [1]. The development leads to a greatly improved observation of growth parameter influences in the MOVPE of GaN. A new growth process is introduced which enhances growth reproducibility [2]. This new growth process is then optimized with respect to the envisaged application. To this end process modeling will be employed. The application envisaged is the AlxGa1−xN/GaNhigh electron mobility transistor (HEMT). At last device results will be presented. All in all it will be shown how fundamental research can drive technology and how basic knowledge can be employed forprocess development with respect to device applications. [less ▲]

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 ▲]

Comparison of AlGaN/GaN MSM varactor diodes based on HFET and MOSHFET layer structures

in Proc. 6th Intern. Conf. Advanced Semicon. Dev. & Microsystems ASDAM’06 (2006)

In this comparative study we investigate the performance of AlGaN/GaN based MSM varactor diodes based on HFET and MOSHFET layer systems. Device fabrication uses standard HFET fabrication technology ... [more ▼]

In this comparative study we investigate the performance of AlGaN/GaN based MSM varactor diodes based on HFET and MOSHFET layer systems. Device fabrication uses standard HFET fabrication technology, allowing easy integration in MMICs. Devices with different electrode geometries are characterized by DC and by S-parameter measurements up to 50 GHz. The HFET based varactors show capacitance ratios up to 14. The MOSHFET based devices, on the other hand, exhibit lower capacitance ratios and poorer stability because of theinsulation layer between electrodes and semiconductor. [less ▲]

Technology related issues regarding fabrication of AlGaN/GaN-based MOSHFETs with GdScO3 as dielectric,

in Proceedings of 6th Intern. Conf. Advanced Semicon. Dev. & Microsystems ASDAM’06 (2006)

Starting out from our well established process for AlGaN/GaN HFETs we discuss ways to enrich the process in order to fabricate Metal-Oxide-Semiconductor HFETs (MOSHFETs) with a Gadolinium Scandate (GdScO3 ... [more ▼]

Starting out from our well established process for AlGaN/GaN HFETs we discuss ways to enrich the process in order to fabricate Metal-Oxide-Semiconductor HFETs (MOSHFETs) with a Gadolinium Scandate (GdScO3) insulation layer. In particular, adequate processing orders, various etching procedures and possible drawbacks of the GdScO3 deposition process on ohmic contacts are discussed. Making use of the gained knowledge we fabricated GdScO3-MOSHFETs for the first time. Compared to a conventional HFET the new device shows a higher saturation drain current and a lower gate leakage current. Nevertheless, the potential insulating properties of GdScO3 are not fully exploited yet and further optimization of the deposition process is needed. [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 ▲]