Threshold voltage control by gate oxide thickness in fluorinated GaN metal-oxide-semiconductor high-electron-mobility transistors

Abstract

This paper demonstrates the compensation of the intrinsic positive charges in Al2O3 gate dielectric by fluorine ions in GaN metal-oxide-semiconductor high-electron-mobility transistors (MOS-HEMTs). Negatively-charged fluorine ions diffused into the oxide from the AlGaN barrier during the 250 °C atomic layer deposition compensate the intrinsic positive charge present in the Al2O3. This compensation is key to control the threshold voltage (Vth) of enhancement-mode (E-mode) transistors. A comprehensive analytical model for the Vth of fluorinated MOS-HEMTs was established and verified by experimental data. This model allows the calculation of the different charge components in order to optimize the transistor structure for E-mode operation. Using the proposed charge compensation, the Vth increases with gate dielectric thickness, exceeding 3.5 V for gate dielectrics 25 nm thick.

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

“…5,6,8 For the control of N it (and bulk oxide charge N ox which can work in the same way), various methods have been presented, such as gate-recess, 9 plasma oxidation of AlN, 10 or fluorination of a gate oxide. 11 Our group has also shown first results indicating that thermal annealing of a plasma-oxidised Al thin film as gate dielectric leads to V th shifts to more positive values due to the presence of oxide-related charge. 12 However, using the plasma-oxidised Al layer, N it has not shown to be sufficiently high to enable a V th , which is higher than one of the Schottky gated references.…”

Control of threshold voltage in E-mode and D-mode GaN-on-Si metal-insulator-semiconductor heterostructure field effect transistors by in-situ fluorine doping of atomic layer deposition Al2O3 gate dielectrics

“…As the positive Al mass should be unchanged, this increase in M can be attributed to the change from lighter O atoms to heavier F atoms. As ALD Al 2 O 3 grown by thermal methods is known to possess intrinsic positive bulk charge, 4 this Sellmeier analysis indicates that the increase in F, with its additional electron and higher electronegativity compared to O, 7 and the effect of the FGA could compensate for the native positive charge that occurs in ALD Al 2 O 3 . Figure 2 shows the results of SIMS analysis for $100 nm of Al 2 3 yields a F concentration of between 0.06 at.…”

“…Following the FGA, the slight reduction seen in the refractive index for F:Al 2 O 3 could be attributed to displacement of O for F within the oxide 4,20 or by a change in density of the films. Figure 1 shows the results for the average oscillator strength, S 0 , the average oscillator position, k 0 , the average single oscillator energy gap in eV, E 0 , and the average oscillator strength in eV, E d .…”

“…10 It was reported that the F-distribution was confined to the top 2 nm of the dielectric and furthermore avoided plasma-induced damage at the interface with the III-nitride. Zhang et al 4 have reported the compensation of the intrinsic positive charges in Al 2 C left the F-distribution almost unchanged. Here, we report an in-situ process for the uniform F doping of alumina throughout the gate oxide thickness deposited by atomic layer deposition.…”

“…3 One way to achieve this is to form a negative charge in the gate region of the device by doping or ion implantation with fluorine (F) ions in the gate region of the device. [3][4][5][6][7] Alternative fluorine treatments have been investigated elsewhere, as a means of ameliorating the relatively high defect densities associated with atomic layer deposition (ALD) of amorphous Al 2 O 3 -nitride device structures. 8 A fluorine-based plasma treatment has been previously described as a method of incorporating negatively charged F ions into the AlGaN barrier of an E-mode high electron mobility transistor (HEMT) and resulted in a positively shifted threshold voltage.…”