Abstract
In this work, we studied the mechanisms and switching properties of AlGaN/GaN high-electron-mobility-transistors (HEMTs) passivated by amorphous-SiN x and monocrystal-like AlN. The effects of interface traps and polarization charges on current collapse are investigated by TCAD simulations and experimental characterizations. Surface/interface deep levels can be compensated by both shallow donor-like traps (SiN x passivation) and polarization charges (AlN passivation) at passivation/heterostructure interface, but with different levels of effectiveness under fast switching conditions. SiN x -passivation introduces shallow donor-like trap states with short time constant that favors a fast emission of trapped electrons in the access region and suppressed current collapse, but nevertheless exhibits more severe time-dependent recovery of dynamic on-resistance. For AlN passivation, interface traps are compensated by the fixed positive polarization charges and the off-state depletion region (in the 2DEG channel) is formed predominantly by electric-field effect, leading to an immediate accumulation of high channel electron concentration after switching the HEMT devices back to on-state and instant response of drain current to gate and drain bias. The field plate structure is necessary in SiN x -passivated devices for both current collapse suppression and electric field alleviation. With AlN passivation, the field plate can be solely designed for achieving more uniform electric field distribution for gate reliability concern without the concern of current collapse.
Highlights
Gallium nitride exhibits great potential in power electronic applications owing to its superior material properties
TCAD SIMULATION RESULTS The transient switching behavior of SiNx- and AlN- passivated GaN-cap/AlGaN/GaN HEMTs are simulated based on a pulsed I-V measurement configuration with drain current (IDS) recorded
With AlN passivation, the device can respond to the fast gate voltage switching quickly,with the IDS and RON almost reaching to the value at static on-state immediately after turning on the device
Summary
Gallium nitride exhibits great potential in power electronic applications owing to its superior material properties. Positive fixed charges with a sheet density of 1.7 × 1013 cm−2 and ten-levels (0.31 eV ≤ EC − ET ≤ 0.60 eV) acceptor-like traps (charge neutral when empty and negative charged when filled with electrons) are applied at AlN/GaN-cap interface in the simulated AlN-passivated device, as shown in Fig. 2 (b). 4 plots the simulated channel electron concentration at AlGaN/GaN interface and the density of filled traps at passivation/GaNcap interface in SiNx and AlN-passivated devices at on-state before stress, off-state, and various time delays (from 1 ns to 100 ms) after off-to-on switching event, which helps explain the transient IDS and RON behavior. Even with a complete ionization of the interface acceptor-like traps, there still maintains a net positive charge with sheet density of 7.4 × 1012 cm−2 at AlN/GaN-cap interface, as channel for SiNx- and AlN-passivated devices are shown in Fig. 6 (a) and (d), respectively.
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