Fig. 1. (Color online) The main requirements in 5G wireless communication^[4].

Fig. 2. (Color online) GaN HEMTs for power electronics applications^[8].

Fig. 3. (Color online) The routine failure analysis procedure for GaN HEMTs.

Fig. 4. (Color online) (a) Schematic GaN HEMT cross section. (b) SEM image depicting damages after the catastrophic failure^[22].

Fig. 5. (Color online) SEM and TEM images revealing different types of failure mechanisms dominant during test under (a) dark and (c) UV conditions. (b) TCAD contour revealing hole distribution at breakdown voltage, under the –6 V gate bias condition^[24].

Fig. 6. (Color online) A sequence of events captured during 50 ns ESD stresses on the drain without gate and with mesa^[25].

Fig. 7. (Color online) (a, c, e) SEM images and (b, d, f) AFM images of three devices with different stressed times^[16].

Fig. 8. (Color online) (a) EMMI images of the device at different stress times. (b, c) TEM image of the failure region depicted in (a)^[30].

Fig. 9. (Color online) (a, b) EMMI images of the HEMT before and after ON-state DC-stress. (c, d) Cross-section EDS mapping of central T-gate finger showing the formation of Ni voids. (e) Aluminium oxidation at a pit^[31].

Fig. 10. (a) STEM of a TiN metal inclusion, which has penetrated the AlGaN layer. (b) A nanocrack extending from a TiN metal inclusion into the channel area^[33].

Fig. 11. (a) A device before loading. (b) The device at the on-set of source-drain leakage. (c) A metal inclusion appears at the drain region. (d) The metal inclusion penetrates the GaN layer. (e) The metal inclusion reaches the GaN-SiC interface. (f) The substrate is completely damaged at last^[19].

Fig. 12. (Color online) (a) De-cap and de-layer operations of the failed device. (b) Simulation of electric field and impact ionization (I.I.) rate distributions along the AlGaN/GaN interface when the V_ds approaches V_peak during the UIS process^[36].

Fig. 13. (Color online) (a) TEM image and (b) EDS cartography (across the blue line) of the Schottky contact of an aged HEMT^[37].

Fig. 14. (Color online) (a) Burn spot locations for 50 W-pulses. (b) Simulated densities of power dissipation for two different pulses shortly before the failure happens. (c) A failure region (Mag = 500×)^[38].

Fig. 15. (Color online) (a) Failure region of the GaN HEMT (CGH-27015, manufactured by Cree, Inc.). (b) FIB image of the breakdown area which is located in the FP. (c) Captured thermal stress distribution of the device. (d) Enlarged stress distribution near the gate^[43].

Fig. 16. (Color online) (a) Optical image of the GaN HEMT before failure. (b) SEM image of the GaN HEMT after failure^[46].

Fig. 17. (Color online) (a) Magnetic field distribution and (b) optical micrograph of the PA layout^[46].

Fig. 18. TEM images of GaN HEMT device irradiated with 1540 MeV Bi ions at a fluence of 1.7 × 10¹¹ ions/cm^2[48]. (a) Cross-section of the gate areas. (b) High-resolution image of the tracks in heterogeneous junction areas as marked in (a). (c) High-resolution image of the tracks at a depth of about 500 nm as marked in (a). (d) Tracks formed in the drain area. (e) Tracks appearing at a depth of about 500 nm as marked in (d).

Fig. 19. TEM images at different V_D during the OFF-state failure tests after the irradiation (2.8 MeV Au⁴⁺ ion species for 60 min to a fluence of 4 × 10¹⁴ ions/cm²)^[49]. Drain voltage: (a) V_d = 0 V, (b) V_d = 10.2 V, and (c) enlarged TEM image of the yellow rectangle area of (b), showing dislocations in the GaN layer.

Table 1. Different failure mechanisms and their corresponding failure phenomena.