Improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistor

Abstract

The authors report on improved transport properties of Al2O3∕AlGaN∕GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). It is found that the drift mobility in the MOSHFET structures with 4nm thick Al2O3 gate oxide is significantly higher than that in HFETs. The zero-bias mobilities are 1950 and 1630cm2∕Vs for the MOSHFET and HFET, respectively. An ∼40% increase of the saturation drain current in the MOSHFETs compared to the HFETs seems to be larger than expected from the passivation effects. The MOSHFET devices show a higher transconductance (with peak values of ∼115mS∕mm) than the HFETs (∼70mS∕mm). Analysis of the device performance indicates a decrease of the parasitic series resistance together with an enhancement of the effective velocity of the channel electrons in the MOSHFET devices.

Enhancement of effective carrier velocity in AlGaN/GaN MOSHFETs with Al2O3 gate oxide

“…The saturation drain current I Ds at the gate voltage V G = 1 V of devices with 2.5 µm gate length increased from ~430 mA/mm for the HFETs to ~600 mA/mm for the MOSHFETs with 4 nm SO-oxide. Nearly identical saturation currents, 410 mA/mm and 570 mA/mm, we reported on HFETs and MOSHFETs with 4 nm MO-oxide, respectively [6]. Figure 1 shows typical characteristics of the extrinsic transconductance vs gate voltage for the MOSHFET (4 nm Al 2 O 3 SO-oxide) and the HFET counterpart.…”

“…Conventional FET fabrication steps (mesaetching isolation, alloyed Ti/Al/Ni/Au ohmic contacts and Ni/Au Schottky metallization) were used for the device preparation with 2.5 µm gate length (for details see Refs. [6] and [7]). Sputtered 3 nm thick Al layer that was subsequently oxidized in dry oxygen was used to prepare Al 2 O 3 gate insulator (called SO-oxide in the next).…”

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

“…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.…”

“…[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. 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.…”

Oxygen defects in amorphous Al2O3: A hybrid functional study

“…[1][2][3][4][5] For this reason, native defects in Al 2 O 3 have been the subject of extensive experimental and theoretical investigations aiming at verifying the presence of deep-level traps in the dielectric. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] The vast majority of theoretical studies performed so far have focused on crystalline phases of Al 2 O 3 .…”