nhan Mi

90 nm gate length enhancement-mode AlGaN/GaN HEMTs with plasma oxidation technology for high-frequency application

High-frequency enhancement-mode (E-mode) AlGaN/GaN high-electron-mobility transistors (HEMTs) with plasma oxidation technology (POT) were fabricated through plasma-enhanced chemical vapor deposition. POT enables the formation of a thin oxide layer in the gate region, which decreases the gate leakage by at least two orders of magnitude compared with conventional recessed gate HEMTs. Ultra-low leakage was achieved in the fabricated device, with Ioff = 9.5 × 10−7 mA/mm and a high ON/OFF ratio of over 109. Good suppression of current collapse was obtained after the application of POT in the access region. The enhancement-mode AlGaN/GaN HEMTs with POT showed an outstanding performance, with a Vth of 0.4 V, a maximum drain current of 965 mA/mm, and an fmax of 272 GHz.

Effect of gate length on breakdown voltage in AlGaN/GaN high-electron-mobility transistor*

The effects of gate length LG on breakdown voltage VBR are investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) with LG = 1 μm~ 20 μm. With the increase of LG, VBR is first increased, and then saturated at LG = 3 μm. For the HEMT with LG = 1 μm, breakdown voltage VBR is 117 V, and it can be enhanced to 148 V for the HEMT with LG = 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage. A similar suppression of the impact ionization exists in the HEMTs with LG > 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG = 3 μm~20 μm, and their breakdown voltages are in a range of 140 V–156 V.

Normally-Off AlGaN/GaN High Electron Mobility Transistors with Thin and High Al Composition Barrier Layers

A GaN-based enhancement-mode high electron mobility transistor (HEMT) with a 1.5 nm GaN/9 nm Al0.65Ga0.35N thin barrier was reported. Without any treatment on barrier layer under the gate, the as-grown HEMTs exhibited a threshold voltage of 0.3 V, a maximum drain current density of 441 mA/mm at VGS = 3 V and a peak extrinsic transconductance of 204 mS/mm at VGS = 1.1 V. At the same time, both a low Schottky leakage current and an insignificant surface defects induced current dispersion were observed. Moreover, drain induction barrier lower (DIBL) effect was determined to be merely 3.28 mV/V at 1 mA/mm for a gate length of 0.5 µm. Additionally, post-gate annealing experiment at step temperatures up to 450 °C was implemented, only causing a minor shift in threshold voltage. These results demonstrated the substantial potential of thin and high Al composition barrier layers for high-voltage and highly reliable enhancement mode operation.

Trap states in enhancement-mode double heterostructures AlGaN/GaN high electron mobility transistors with different GaN channel layer thicknesses

This is the report on trap states in enhancement-mode AlGaN/GaN/AlGaN double heterostructures high electron mobility transistors by fluorine plasma treatment with different GaN channel layer thicknesses. Compared with the thick GaN channel layer sample, the thin one has smaller 2DEG concentration, lower electron mobility, lower saturation current, and lower peak transconductance, but it has a higher threshold voltage of 1.2 V. Deep level transient spectroscopy measurements are used to obtain the accurate capture cross section of trap states. By frequency dependent capacitance and conductance measurements, the trap state density of (1.98–2.56) × 1012 cm−2 eV−1 is located at ET in a range of (0.37–0.44) eV in the thin sample, while the trap state density of (2.3–2.92) × 1012 cm−2 eV−1 is located at ET in a range of (0.33–0.38) eV in the thick one. It indicates that the trap states in the thin sample are deeper than those in the thick one.

Improved on-state performance of AlGaN/GaN Fin-HEMTs by reducing the length of the nanochannel

In this letter, AlGaN/GaN Fin-HEMTs with different nanochannel geometric parameters were fabricated and characterized. The drain current density, transconductance, and on-resistance were improved by reducing the length of the nanochannel, which was attributed to the modulation of access resistance by changing the length of the nanochannel. The threshold voltage shifted to the positive direction with the decrease in the width of the nanochannel and showed the independence on the length of the nanochannel. With the reduction in the length of the nanochannel, the gate swing was increased by suppressing the increase of source resistance, improving the linearity of transconductance.

Influence of the built-in electric field induced bby low power fluorine plasma implantation on the reliability of AlGaN-GaNHEMTs

The reliability of traditional T-gate AlGaN/GaN high electron mobility transistor (HEMT) fabricated by the low power fluorine plasma treatment was investigated by applying the off-state high electric field stress. The new electrical degradation phenomenon of AlGaN/GaN HEMT with low power fluorine plasma treatment is discovered. The electrical parameters show a rapid degradation in a short time, and then keeping mostly unchangeable. The migration phenomenon of fluorine ions is further validated by the electron redistribution and breakdown voltage enhancement after off-state stress. Due to fluorines strong electronegativity, the migration of fluorine can induce build-in electric field. Thereby, it would prevent the drift of the subsequent fluorine ions and alleviate further degradation of AlGaN/GaN HEMT.

Influence of thermal annealing on AlGaN/GaN HEMT by fluorine plasma treatment

The influence of thermal annealing on four kinds of AlGaN/GaN high electron mobility transistors (HEMTs) with different fluorine plasma treatment power were compared and analyzed in detail. A thin fluorinated layer between the Schottky metal and the AlGaN barrier layer which produced with fluorine plasma treatment was conformed by the comparison of Schottky reverse gate leakage current before annealing and after annealing. The maximum saturation current and the peak transconductance of HEMTs decreased with the fluorine plasma treatment power increasing before annealing, and they were recovered partially after annealing. The hysteresis of double sweep curves by fluorine plasma treatment was enlarged. F− ions could introduce the acceptor state in the barrier layer, and high temperature could eliminate some trap states introduced by fluorine plasma treatment.

The improvement of breakdown voltage in AlGaN/GaN HEMT by using high-k dielectric La 2 O 3 passivation

The AlGaN/GaN high electron mobility transistor using 30-nm ALD La<inf>2</inf>O<inf>3</inf> passivation has been fabricated. Compared with the non-passivation HEMT, the breakdown voltage Vbr of La<inf>2</inf>O<inf>3</inf> passivation HEMT can be improved from 115 V to 134 V. 2-D simulation is adopted to explain the phenomenon. The reason for enhanced Vbr in La<inf>2</inf>O<inf>3</inf> passivation HEMT is due to high permittivity e<inf>r</inf> of La<inf>2</inf>O<inf>3</inf> dielectric with drain side wall and AlGaN/GaN HEMT can form metal-insulator-semiconductor (MIS) structure which can modulate electric field distribution. Based on the results, the introduction of high-K dielectric passivation can enhance breakdown voltage as well as simplify the process step.

Recessed-gate quasi-enhancement-mode AlGaN/GaN high electron mobility transistors with oxygen plasma treatment*

In this paper, the enhancement-mode AlGaN/GaN HEMT combined with the low damage recessed-gate etching and the optimized oxygen plasma treatment was fabricated. Scanning electron microscope/energy dispersive spectrometer (SEM/EDS) method and x-ray photoelectron spectroscopy (XPS) method were used to confirm the formation of oxides. Based on the experimental results, the obtained enhancement-mode HEMT exhibited a threshold voltage of 0.5 V, a high peak transconductance of 210 mS/mm, and a maximum drain current of 610 mA/mm at the gate bias of 4 V. Meanwhile, the on/off current ratio of enhancement-mode HEMT was as high as 108, drain induced barrier lowering (DIBL) was as low as 5 mV/V, and subthreshold swing (SS) of 80 mV/decade was obtained. Compared with the conventional HEMT, the Schottky reverse current of enhancement-mode HEMT was three orders of magnitude lower, and the off-state breakdown voltage of which was higher. In addition, a power gain cutoff frequency (f max) of the enhancement-mode HEMT was larger than that of the conventional one.