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RTS amplitude (symbols) and gate current (solid lines) as a function of forward bias Vgs , F for the unstressed (curves RTS-1, IV-1) and stressed (curves RTS-2, IV-2) device. The data are for the same device. The device was stressed by step-stress experiments in the range from −10 to −80 V stepping with −2 V every 2 min. The inset shows RTS fluctuations of RTS-1 in the unstressed device at Vgs , F = 0.74 V. RTS amplitude ΔIRTS , and pulse widths in the upper (t+ ) and lower (t −) RTS states are indicated. Ambient temperature, T, was 297 K.
(a) Schematic band energy (E) diagram along the gate edge with one percolation path; the origin of the x and y axes is at the AlGaN/GaN interface and in the middle of the percolation path, respectively. (b) Band diagram inside the percolation path with occupied and empty trap. The trap is spatially located at x = −xd and y = 0, see also (a). The x-axis view is a cut in the E-x plane at y = 0. The y-axis view is a cut in the E-y plane at x = −xd . RTS is governed by electron trapping from GaN (dashed blue downward arrows; both tunneling and thermo-ionic pathways for capture are shown) followed by emission (e.g., tunneling) to gate metal (red leftward arrow). A tentative band diagram for the occupied (i.e., negative) trap is given by dotted lines. (c) Band diagram in the percolation path for the case of RTS governed by carrier exchange between the GaN channel and the trap. The emission process is marked by the red arrows. The situation is shown for two forward biases (Vgs , F2 > Vgs , F1 ), demonstrating how the trap thermal activation energy ΔECT increases with increase in Vgs , F . ET is trap level, EFS and EFM are Fermi levels for GaN and gate metal. We consider that, at forward bias (i.e., accumulation), all the applied bias drops in the AlGaN barrier.
Time evolution of reverse gate current during the step-stress experiment with 8 min holding at each step, starting at Vgs = −10 V, with steps of −2 V. Slow RTS fluctuations with mean pulse widths below a minute can be observed. T = 297 K.
Overview of the mean pulse widths in the upper (〈t+ 〉—filled symbols) and lower (〈t −〉—open symbols) RTS states for five RTS fluctuators in four devices with intrinsic or stress-induced RTS. RTS no. 1 and 2 are those from Fig. 1 for the same device. The stressing condition and extracted parameters for numbered RTS are: (1) unstressed, α+ = 0.8, α − = 0.8, and β = 1.0; (2) stressed, α+ = 0.8, α − = 0, and β = 1.5; (3) unstressed, α+ = 0.9, α − = 0, and β = 1.1; (4) unstressed, α+ = 1, α − = 0, and β = 1.1; and (5) unstressed, α+ = 1.2, α − = 0, and β = 2.1. The functional dependence exp(−α+Vgs , F /Vt ) for α+ = 1 is indicated; T = 297 K.
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