We report on SiO 2 / AlGaN / GaN metal-oxide-semiconductor heterostructure field-effect transistors ͑MOSHFETs͒, which exhibit a 6.7 W / mm power density at 7 GHz. Unpassivated and SiO 2-passivated heterostructure field-effect transistors ͑HFETs͒ were also investigated for comparison. Deposited 12 nm thick SiO 2 yielded an increase of the sheet carrier density from 7.6ϫ 10 12 to 9.2ϫ 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 f T of 24 GHz and a maximum frequency of oscillation f max 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.

No abstract

No abstract

Conductivity and Hall effect measurements were performed before and after Si 3 N 4 passivation of intentionally undoped and doped AlGaN/GaN heterostructures on Si and SiC substrates. An increase of the sheet carrier density ͑up to ϳ30%͒ and a slight decrease of the electron mobility ͑less than 10%͒ are found in all samples after passivation. The passivation induced sheet carrier density is 1.5-2ϫ10 12 cm Ϫ2 in undoped samples and only 0.7ϫ10 12 cm Ϫ2 in 5-10ϫ10 18 cm Ϫ3 doped samples. The decrease of the electron mobility after passivation is slightly lower in highly doped samples. The channel conductivity in both types of unpassivated samples on Si and SiC substrates increases with an increase in doping density. After passivation, a well-resolved increase of channel conductivity is observed in the undoped or lightly doped samples and nearly the same channel conductivity results in the highly doped samples.

Sheet carrier concentration and low-field drift mobility of intentionally undoped and modulation-doped AlGaN/GaN heterostructures on SiC substrate were evaluated by capacitance-voltage and channel conductivity measurements. Sheet carrier concentration and average mobility at 0 V gate bias correspond to standard Hall results. Sheet carrier density increases from 6.8×1012 cm−2 for the undoped sample up to 1×1013 cm−2 for the device with the highest doping concentration, while the mobility decreases from 1800 to 1620 cm2/V s. The local mobility, on the other hand, depends only on the actual sheet carrier density and is not influenced by the doping concentration of the carrier supply layer. It reaches a maximum value of 2100 cm2/V s at a carrier density of 3×1012 cm−2.

PACS 81.65.Rv, 85.30.De, 85.30.Tv This paper reports on properties of intentionally undoped AlGaN/GaN/sapphire-based high electron mobility transistors (HEMTs) before and after passivation with SiO 2 and Si 3 N 4 . Our results indicate that the DC performance of the AlGaN/GaN HEMTs improved significantly as the stress in the passivation layer increased from compressive to tensile. It corresponded to changes in the sheet carrier concentration. Unlike the DC properties, RF properties of the HEMTs were less sensitive to the stress.

We report on a correlation between the gate leakage currents and the drain current collapse of GaN∕AlGaN∕GaN high electron mobility transistors. Unpassivated devices on intentionally undoped and doped (Si, 5×1018cm−3) heterostructures were investigated. We observed in the devices that the larger the gate leakage current, the smaller the drain current collapse measured at 50ns gate-voltage pulse turn on, and this correlation is independent of the doping of the structure. The correlation holds for two orders of magnitude in the gate-leakage current and up to 15% in drain current collapse. We believe that the leakage current can modulate trapped surface charge so that the time constant of the current collapse becomes much faster and dependent on the amount of leakage current itself.

No abstract