Investigations of HfO2∕AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors

Abstract

We report the studies of AlGaN∕GaN metal-oxide-semiconductor high electron mobility transistors (MOS-HEMTs) using reactive-sputtered HfO2 as the gate dielectric and the surface passivation layer. X-ray photoemission method reveals a conduction-band offset of 1.71eV for the HfO2∕GaN heterostructure. The dielectric constant of HfO2 is estimated to be 21 by capacitance-voltage measurements. MOS-HEMTs with a 1.5-μm-long gate exhibit a maximum drain current of 830mA∕mm and a peak transconductance of 115mS∕mm, while the gate leakage current is at least five orders of magnitude lower than that of the reference HEMTs. Good surface passivation effects of HfO2 have also been confirmed by pulsed gate measurements, with MOS-HEMTs showing a significant drain current recovery from current collapse observed in HEMTs.

Investigation of the interface between silicon nitride passivations and AlGaN/AlN/GaN heterostructures by C(V) characterization of metal-insulator-semiconductor-heterostructure capacitors

“…V 2A is correlated with the pinch-off voltage of a MISHFET device. 7,19 At gate biases higher than the barrier accumulation voltage ͑V BA ͒ electrons will start to transfer into the barrier of the heterostructure. V BA is arbitrarily chosen where there is a substantial increase in the slope of the capacitance curve.…”

“…The situation can be approximated with a parallel plate capacitor using the 2DEG and the gate metal for conductive surfaces, with a dielectric containing both the barrier and the passivation. 7 The voltage where the capacitance is half of C tot is arbitrarily chosen as the 2DEG accumulation voltage ͑V 2A ͒. V 2A is correlated with the pinch-off voltage of a MISHFET device.…”

“…Chen et al 6 investigate GaN-based MIS and MISH structures deposited with a SiO 2 passivation. Liu et al 7 measure C͑V͒ characteristics of a HfO 2 passivated AlGaN/GaN heterostructure. In a more recent report Miczek et al 8 investigate MISH capacitors passivated with silicon nitride and Al 2 O 3 dielectrics.…”

Effects of interface states and temperature on the C-V behavior of metal/insulator/AlGaN/GaN heterostructure capacitors

“…15,18 Although the standard high frequency capacitancevoltage ͑C-V͒ measurement at room temperature ͑RT͒ is usually done on metal/insulator/semiconductor heterostructure ͑MISH͒ capacitors and/or metal/semiconductor heterostructure ͑MSH͒ Schottky diodes before the fabrication and characterization of the MISHFET devices, the C-V data are often used only to estimate the thicknesses of the insulator film and/or the AlGaN layer 1,4,12,16,19 or to calculate the 2DEG density. 1,20 Although some authors have claimed that the slope of the MISH C-V curve can be used as a measure of the electronic quality of the insulator/AlGaN interface, 4,11,13 this claim should be considered very carefully because the C-V slope in a metal/AlGaN/GaN structure depends on the quality of the AlGaN/GaN interface and other factors, 21 and there is no well known and tested procedure for the analysis of C-V curves from a metal/insulator/AlGaN/GaN structure to extract the state density at the insulator/AlGaN and AlGaN/GaN interfaces. Some other authors have stated that the shifts of the C-V curve and of the threshold voltage ͑V th ͒ with respect to theoretical values are related to the charge in the insulator and at the insulator/AlGaN interface.…”

“…While keeping the merits of conventional Schottky-gate-based HFETs, i.e., a high density of two-dimensional electron gas ͑2DEG͒ at the AlGaN/GaN interface, high cutoff and maximum frequencies, and the thermal and chemical stability of AlGaN and GaN, MISHFETs offer many advantages over HFETs, such as lower gate leakage current, higher breakdown voltage, better thermal stability of the gate, mitigation of current collapse, a wider range of gate voltage sweep, and higher maximum drain current and output power. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] These features are crucial for applications in high-power, high-temperature electronics, 7,17 particularly to realize low on-resistance and normally off highpower FETs. 15,18 Although the standard high frequency capacitancevoltage ͑C-V͒ measurement at room temperature ͑RT͒ is usually done on metal/insulator/semiconductor heterostructure ͑MISH͒ capacitors and/or metal/semiconductor heterostructure ͑MSH͒ Schottky diodes before the fabrication and characterization of the MISHFET devices, the C-V data are often used only to estimate the thicknesses of the insulator film and/or the AlGaN layer 1,4,12,16,19 or to calculate the 2DEG density.…”