Electrical effects of SiNx deposition on GaN MESFETs

CNRS, Villeneuve
Electronics Letters (Impact Factor: 0.93). 05/2001; 37(8):527 - 528. DOI: 10.1049/el:20010324
Source: IEEE Xplore


The electrical effects of SiNx deposition on GaN
MESFETs have been investigated. Significant effects induced from the
dielectric coating have been observed depending on the deposition
temperature used in the technological process. A power density increase
of 30% has been observed after the device passivation performed at

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    ABSTRACT: A surface leakage test structure is used to isolate the surface and bulk leakage currents in AlGaN/GaN based devices. Passivation of post-processed devices with stoichiometric Si3N4 resulted in reduced surface leakage, which suggests that surface passivation acts to suppress the AlGaN surface conduction, possibly through a reduction in surface states. However, passivation with low temperature grown SiNx, which has a high density of interfacial states increased the surface leakage component instead. This implies that surface conduction is critically dependent on the amount of surface states present. The surface leakage component is also found to be thermally activated with an activation energy of 0.19 eV. When the devices are driven to hard breakdown, a sharp rise in the surface current is typically observed, which strongly suggests that breakdown in these devices is dominated by surface edge effects.
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    ABSTRACT: We present an experimental analysis on the effect of dielectric stress on the electrical characteristics of AlGaN/GaN HFETs. Issues such as maximum current (I<sub>d-max</sub>), gate leakage and current collapse are presented. Different dielectric deposition conditions were used to vary the amount of stress induced on the wafer and the devices were measured before and after passivation. A striking feature observed was the strong dependence of I<sub>d-max</sub> on the amount of stress induced by the dielectric. I<sub>d-max</sub> increases when the stress is tensile and reduces when it is compressive. The rise in leakage current was found to be dependent on the dielectric film itself and not on the stress induced, which suggests that a surface effect is responsible for the leakage mechanism.
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    ABSTRACT: The influence of dielectric stress on the direct current (DC) electrical characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) has been investigated. Dual-frequency plasma deposition was used to vary the amount of stress induced by a passivating dielectric on the surface of the devices. Initial data suggested a strong influence from the induced dielectric stress, but the low-frequency, radio-frequency (RF) excitation of the plasma deposition process was found to induce a severe nonreversible damage to the exposed AlGaN surface through N ion bombardment. The consequence is a drastic reduction of the sheet carrier concentration and mobility of the two-dimensional electron gas (2DEG). Subsequently, an alternative damage-free technique using a helium precursor was used to obtain compressive films. Based on the results, uniform dielectric stress has a minimal impact on the polarization charges within the AlGaN barrier.
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