Recess-free enhancement-mode AlGaN/GaN RF HEMTs on Si substrate

Enhancement-mode(E-mode)GaN-on-Si radio-frequency(RF)high-electron-mobility transistors(HEMTs)were fabri-cated on an ultrathin-barrier(UTB)AlGaN(<6 nm)/GaN heterostructure featuring a naturally depleted 2-D electron gas(2DEG)channel.The fabricated E-mode HEMTs exhibit a relatively high threshold voltage(VTH)of+1.1 V with good uniformity.A maxi-mum current/power gain cut-off frequency(fT/fMAX)of 31.3/99.6 GHz with a power added efficiency(PAE)of 52.47%and an out-put power density(Pout)of 1.0 W/mm at 3.5 GHz were achieved on the fabricated E-mode HEMTs with 1-μm gate and Au-free ohmic contact.

High power-added-efficiency AlGaN/GaN HEMTs fabricated by atomic level controlled etching

An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl_(2)-only ACE and BCl^(3)/Cl_(2)ACE,respectively.The mixed radicals of BCl_(3)/Cl_(2)were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl_(3)/Cl_(2)ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode.

An X-band GaN combined solid-state power amplifier

Based on a self-developed A1GaN/GaN HEMT with 2.5 mm gate width technology on a SiC substrate, an X-band GaN combined solid-state power amplifier module is fabricated. The module consists of an AIGaN/GaN HEMT, Wilkinson power couplers, DC-bias circuit and microstrip line. For each amplifier, we use a bipolar DC power source. Special RC networks at the input and output and a resistor between the DC power source and the gate of the transistor at the input are used for cancellation of self-oscillation and crosstalk of low-frequency of each amplifier. At the same time, branches of length 3λ/4 for Wilkinson power couplers are designed for the elimination of self-oscillation of the two amplifiers. Microstrip stub lines are used for input matching and output matching. Under Vds = 27 V, Vgs = -4.0 V, CW operating conditions at 8 GHz, the amplifier module exhibits a line gain of 5.6 dB with power added efficiency of 23.4%, and output power of 41.46 dBm （14 W）, and the power gain compression is 3 dB. Between 8 and 8.5 GHz, the variation of output power is less than 1.5 dB.