Transport mechanism of reverse surface leakage current in AlGaN/GaN high-electron mobility transistor with SiN passivation

The transport mechanism of reverse surface leakage current in the AlGaN/GaN high-electron mobility transistor（HEMT） becomes one of the most important reliability issues with the downscaling of feature size.In this paper,the research results show that the reverse surface leakage current in AlGaN/GaN HEMT with SiN passivation increases with the enhancement of temperature in the range from 298 K to 423 K.Three possible transport mechanisms are proposed and examined to explain the generation of reverse surface leakage current.By comparing the experimental data with the numerical transport models,it is found that neither Fowler-Nordheim tunneling nor Frenkel-Poole emission can describe the transport of reverse surface leakage current.However,good agreement is found between the experimental data and the two-dimensional variable range hopping（2D-VRH） model.Therefore,it is concluded that the reverse surface leakage current is dominated by the electron hopping through the surface states at the barrier layer.Moreover,the activation energy of surface leakage current is extracted,which is around 0.083 eV.Finally,the SiN passivated HEMT with a high Al composition and a thin AlGaN barrier layer is also studied.It is observed that 2D-VRH still dominates the reverse surface leakage current and the activation energy is around 0.10 eV,which demonstrates that the alteration of the AlGaN barrier layer does not affect the transport mechanism of reverse surface leakage current in this paper.

Surface Leakage Currents in SiN and Al_2O_3 Passivated AlGaN/GaN High Electron Mobility Transistors

Surface leakage currents of A1GaN/GaN high electron mobility transistors are investigated by utilizing a circular double-gate structure to eliminate the influence of mesa leakage current. Different mechanisms are found under various passivation conditions. The mechanism of the surface leakage current with AI2 03 passivation follows the two-dimensional variable range hopping model, while the mechanism of the surface leakage current with SiN passivation follows the Frenkel-Poole trap assisted emission. Two trap levels are found in the trap-assisted emission. One trap level has a barrier height of 0.22eV for the high electric field, and the other trap level has a barrier height of 0.12eV for the low electric field.

A novel Si-rich SiN bilayer passivation with thin-barrier AlGaN/GaN HEMTs for high performance millimeter-wave applications

We demonstrate a novel Si-rich SiN bilayer passivation technology for AlGaN/GaN high electron mobility transistors(HEMTs)with thin-barrier to minimize surface leakage current to enhance the breakdown voltage.The bilayer SiN with 20-nm Si-rich SiN and 100-nm Si_(3)N_(4) was deposited by plasma-enhanced chemical vapor deposition(PECVD)after removing 20-nm SiO_(2)pre-deposition layer.Compared to traditional Si_(3)N_(4) passivation for thin-barrier AlGaN/GaN HEMTs,Si-rich SiN bilayer passivation can suppress the current collapse ratio from 18.54%to 8.40%.However,Si-rich bilayer passivation leads to a severer surface leakage current,so that it has a low breakdown voltage.The 20-nm SiO_(2)pre-deposition layer can protect the surface of HEMTs in fabrication process and decrease Ga–O bonds,resulting in a lower surface leakage current.In contrast to passivating Si-rich SiN directly,devices with the novel Si-rich SiN bilayer passivation increase the breakdown voltage from 29 V to 85 V.Radio frequency(RF)small-signal characteristics show that HEMTs with the novel bilayer SiN passivation leads to f_(T)/f_(max) of 68 GHz/102 GHz.At 30 GHz and V_(DS)=20 V,devices achieve a maximum P_(out) of 5.2 W/mm and a peak power-added efficiency(PAE)of 42.2%.These results indicate that HEMTs with the novel bilayer SiN passivation can have potential applications in the millimeter-wave range.