A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3μm AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating（SI） 4H-SiC substrate by MOCVD. Over the 12-14 GHz frequency range,the single chip amplifier demonstrates a maximum power of 38 dBm（6.3 W）, a peak power added efficiency（PAE） of 24.2%and linear gain of 6.4 to 7.5 dB under a 10%duty pulse condition when operated at V_（ds） = 25 V and V_（gs） = -4 V.At these power levels,the amplifier exhibits a power density in excess of 5 W/mm.
The impacts of varying layout geometries on the channel temperature of multi-finger AIGaN/GaN HEMTs are investigated by three-dimensional （3-D） thermal simulations. Micro-Raman thermography is selected to obtain a detailed and accurate temperature distribution of the sample for the verification of the 3-D thermal models. Thermal boundary resistance （TBR） plays an important role in the temperature distribution and is taken into account in the thermal model in order to improve the accuracy of the simulated results. The influence from the number of fingers, finger width and gate pitch on the gate temperature are systematically analysed using 3-D thermal simulations with validated model parameters. Furthermore, a robust method that could efficiently reduce the thermal crosstalk of multi-finger AlGaN/GaN HEMTs is proposed to optimize the thermal design of the device.
The current voltage （IV） characteristics are greatly influenced by the dispersion effects in A1GaN/CaN high electron mobility transistors. The direct current （DC） IV and pulsed IV measurements are performed to give a deep investigation into the dispersion effects, which are mainly related to the trap and self-heating mechanisms. The results show that traps play an important role in the kink effects, and high stress can introduce more traps and defects in the device. With the help of the pulsed IV measurements, the trapping effects and self-heating effects can be separated. The impact of time constants on the dispersion effects is also discussed. In order to achieve an accurate static DC IV measurement, the steady state of the bias points must be considered carefully to avoid the dispersion effects.
We report a high power Ku band internally matched power amplifier （IMPA） with high power added efficiency （PAE） using 0.3 μm A1GaN/GaN high electron mobility transistors （HEMTs） on 6H-SiC substrate. The intemal matching circuit is designed to achieve high power output for the developed devices with a gate width of 4 mm. To improve the bandwidth of the amplifier, a T type pre-matching network is used at the input and output circuits, respectively. After optimization by a three-dimensional electromagnetic （3D-EM） simulator, the amplifier demonstrates a maximum output power of 42.5 dBm （17.8 W）, PAE of 30% to 36.4% and linear gain of 7 to 9.3 dB over 13.8-14.3 GHz under a 10% duty cycle pulse condition when operated at Vas = 30 V and Vgs = -4 V. At such a power level and PAE, the amplifier exhibits a power density of 4.45 W/mm.
Yellow and blue luminescence in undoped GaN layers with different resistivities are studied by cathodoluminescence.Intense yellow and blue luminescence bands are observed in semi-insulating GaN,while in n-GaN the yellow luminescence and blue luminescence bands are very weak.The stronger yellow and blue luminescences in semi-insulating GaN are correlated to the higher edge-type dislocation density.The scanning cathodoluminescence image reveals strong defect-related luminescence at the grain boundaries where the dislocations accumulate.It is found that the relative intensity of the blue luminescence band to the yellow luminescence band increases with the cathodoluminescence beam energies and is larger in n-GaN with a lower density of edge-type dislocations.An approximately 3.35eV shoulder next to the near-band-edge peak is observed in n-GaN but not in semi-insulating GaN.A redshift of the near-band-edge peak with cathodoluminescence beam energy is observed in both samples and is explained by internal absorption.
The method of multi-bias capacitance voltage measurement is presented. The physical meaning of gate-source and gate-drain capacitances in AlGaN/GaN HEMT and the variations in them with different bias conditions are discussed. A capacitance model is proposed to reflect the behaviors of the gate-source and gate-drain capacitances, which shows a good agreement with the measured capacitances, and the power performance obtains good results compared with the measured data from the capacitance model.
