| Gallium nitride(GaN)materials have excellent physical properties,such as the strong breakdown electric field,high electron saturation rate and electron mobility.Therefore,GaN-based wide band-gap III nitrides semiconductors are very suitable for preparing power microwave electronic devices,such as AlGaN/GaN high electron mobility transistor(HEMT).However,GaN-based devices suffer from much higher leakage current than the theoretical prediction,.In particular,when the device is under a long-term high temperature and pressure condition,the reverse current will increase gradually,occurring an obvious degradation or failure,threatening the the device’s reliability greatly.Low-frequency noise technology is one of the reliability analysis methods for studying the dynamic characteristics of defects,It can obtain important parpmeters such as the energy level depth and time constant related to the defect,which is very helpful for understanding the carrier transport process related to the defect.Emission Microscopy is one of the three major failure analysis tools for device defect location.Its basic principle is to locate the location of the failure point by capturing the photons emitted by the failure point,which can be used to analyze the relationship between the device’s light-emitting phenomenon and the failure mechanism.In view of this,this article takes GaN-based Schottky diodes and light-emitting diodes(LED)as the research objects,and carries out the following research:1.Setting up a low-frequency noise test system.The system adopts the GPIB communication protocol and the python programming languages,and the frequency range is0.3 Hz-3 k Hz.From the low-frequency current noise power spectrum some critical parameters such as the noise amplitude and time constant can be obtained.Conventional electrical testing can only obtain the static parameters of the device,and low-frequency noise can analyze the defect state,which is a powerful supplement to the study of carrier transport.2.Set up a failure hotspot location system.The system uses a high-sensitivity CMOS scientific research camera,and a software interface programed by Labview and Python,which can realize many functions,such as the real-time image display,static image capturing,hotspot locating,and video recording.The sensitive wavelength range is 400-1000 nm,which is very suitable for the wide-bandgap semiconductor devices,such as GaN-based LED and HEMT.3.Study the forward current transport mechanism and low-frequency noise characteristics of GaN Schottky diodes.The results show that: 1)The thermal emission mechanism is dominant in the forward high voltage region,and the effective barrier height is about 1.25 eV;2)Dislocation-related defect-assisted tunneling current dominates in the forward low-bias region,and the effective barrier height is about 0.92 eV(T=300 K);3)Lorentz-type noise appears at very small current and very low frequency,The typical time constant is about 30 ms(I=1 μA);4)The low frequency 1/f noise is dominant at higher frequencies and currents,and the transport is mainly affected by the random fluctuation of the barrier height.4.Study the dynamic degradation behavior of GaN-based LED.The results show that during the high reverse bias,the reverse leakage current increases gradually,and the number of failure points and the amplitude of low-frequency noise also increase correspondingly.We believe that the current degradation is mainly caused by the generation of new dislocations.The high-density shallow-level donor states around the dislocations act as the local tunneling channels,making it easier for electrons to tunnel from the valence band to a lowered conduction band. |
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