Fabrication of AlGaN/GaN MIS‐HFET using an Al ₂ O ₃ high k dielectric

Abstract

We report on a metal-insulator-semiconductor AlGaN/GaN heterostructure field-effect transistor (MIS-HFET) using Al 2 O 3 simultaneously for channel passivation layer and as a gate insulator which was deposited by plasma enhanced atomic layer deposition(PE-ALD). Capacitance-voltage measurements show successful surface passivation by the Al 2 O 3 dielectric layer. For a gate length 1.2 µm with 15 µm sourceto-drain spacing the maximum drain current was 1.22 A/mm, the maximum transconductance was 166 mS/mm and the gate leakage current was 4 nA/mm at V gs = -20 V which is at least three orders of magnitude lower than that of conventional AlGaN/GaN HFETs. IntroductionThe AlGaN/GaN heterostructure field effect transistor (HFET) has a great potential for high voltage, current, and power device applications due to its inherent wide bandgaps, high electron saturation velocity, and piezoelectric field-induced high 2-DEG the density at hetero-interface [1][2][3]. Many research works have been carried out to improve the power and high frequency characteristics of the nitride-based HFETs [4]. However, it has been observed that the Schottky gate of HFET tends to degrade with large gate leakage current and cause an occasional current collapse when the HFETs are operating under high power and high frequency conditions [5]. The degradation of the gate leads to premature breakdown and, hence, an adverse effect on device performances such as output power, rf efficiency, and noise figure. Such a premature breakdown is caused by the gate-drain diode breakdown as a result of the thermionic emission, crystal defects due to lattice mismatch, or the thermal effect as a consequence of the surface hopping conduction of the gate leakage current.Various gate insulation layers, such as SiO 2 , Si 3 N 4 , Ga 2 O 3 , and AlN have been employed as one of the possible solutions to solve the gate leakage problem by passivating the surface [6]. Other groups showed that a thin SiO 2 or Si 3 N 4 layer under the gate is effectively reducing the gate leakage current by several orders. Another advantage of using the insulating layer was thought that it reduces the electrical field in the underlying nitride semiconductor and, therefore, increase the gate breakdown voltage [7].

Gate leakage and electrical performance of AlGaN/GaN MIS-type HFET with evaporated silicon oxide layer

“…However, there are still problems in the development of the devices; especially high gate leakage current and current collapse. To reduce the gate leakage current, metalinsulator-semiconductor (MIS) structures with Al 2 O 3 [3,4], Sc 2 O 3 [5], Si 3 N 4 [6,7], SiO 2 [8,9] have been proposed. These GaN MIS FETs have shown superior performance in both DC and RF.…”

Controlling the interface charge density in GaN-based metal-oxide-semiconductor heterostructures by plasma oxidation of metal layers

“…Sample Al features the lowest capacitance, most likely due to the rather low relative permittivity r for Al 2 O 3 of about 9. 7,14 The oxide capacitance of the AlO x layer in this study is 181 nF/cm 2 . With the oxide thickness of 5.5 nm extracted from the TEM image, the resulting r would be extremely low with a value of about 1.1.…”

Processes and Device Technologies for AlGaN/GaN High Electron Mobility Transistors

“…The gate leakage in these devices can be reduced by using MIS-HEMT structures. Devices with various dielectrics such as SiO x , SiN x , Al 2 O 3 , ZrO 2 have been studied (6,7). The leakages in these devices are 3-4 orders of magnitude lower than those of conventional Schottky gate HEMTs.…”