Analysis of High-Frequency Behavior of AlGaN/GaN HEMTs and MIS-HEMTs under UV Illumination

Abstract

The high-frequency characteristics of AlGaN/GaN high-electron-mobility transistors (HEMTs) and metal-insulator-semiconductor HEMTs (MIS-HEMTs) are investigated under ultraviolet (UV) radiation with 365 nm wavelength. When HEMTs and MIS-HEMTs are illuminated with an UV source, their drain currents increase apparently owing to the generated photocurrent. Nevertheless, they show different high-frequency response to the UV light. For HEMTs, the peak cutoff frequency (fT) and maximum oscillation frequency (fmax) of illuminated devices are 20% and 10% higher than those in dark condition, respectively, owing to the increased transconductance. For MIS-HEMTs, however, their high-frequency performances are degraded when transistors are subject to light exposure. The degradations of peak fT and fmax are around 3.7% and 18%, respectively. The small-signal model parameters relevant to the high-frequency characteristics were extracted to explain these phenomena. Additional trapped charges in the SiN gate dielectric induced by UV light would be responsible for the degraded high-frequency parameters in illuminated MIS-HEMTs. These experimental results are important for designing a suitable GaN-based HEMT for optoelectronic applications.

Analysis of Trapping Effect on Large-Signal Characteristics of GaN HEMTs Using X-Parameters and UV Illumination

“…(1) The average drain current in HEMT and MIS-HEMT increases. The light-enhanced drain current is consistent with the dc measurement result [ 30 ]. (2) The peak-to-peak amplitude of drain current, which is associated with , for the HEMT under UV illumination is higher than that in the dark environment.…”

“…The suppression of buffer-related charge trapping under UV illumination has been reported based on the pulse measurement method [ 28 ]. In previous literature [ 29 ], it was mentioned that the trapped electrons may also release from the surface state after gaining the photon energy, but this phenomenon was not noticeable in our device [ 30 ]. The photoconductive effect increases the 2-DEG concentration, which enhances the transconductance (g m ) and reduces the source/drain access resistances.…”

“…When electrons are captured by the traps near the gate edge in the GaN buffer, the 2-DEG concentration in the gate–drain access region is depleted, leading to a high drain resistance. The suppression of buffer-related charge trapping by UV light will therefore lower the drain resistance [ 30 ]. As a result, the illuminated device exhibits higher than the dark one.…”