Study on drain bias dependence of Y-parameters under on-state condition in GaN HEMTs using low-frequency vector network analyzer and device simulation

Abstract

The drain bias dependence of low-frequency Y-parameters under on-state conditions in Gallium Nitride high electron mobility transistors (GaN HEMTs) is investigated using experimental results and device simulation. The Y-parameters for broadband frequencies from 10 Hz to 100 MHz were systematically measured using a vector network analyzer for drain voltage from 3 to 30 V at the gate voltage of 0 V from room temperature to 120 degrees Celsius. Six signals with the peaks were observed in the imaginary parts (Im) of Y₂₂ and Y₂₁. These peaks were categorized into two groups. One is that the peaks appeared around 5 MHz and have negative slopes in Arrhenius plots. Another is that the peaks appeared below 150 kHz and have an activation energy that can be estimated from Arrhenius plots. The second group was further divided into peaks appeared in both Im(Y₂₂) and Im(Y₂₁), and those that appeared only in Im(Y₂₁). The device simulation including self-heating effects was performed using the trap parameters estimated from the experimental results. Both DC and Y-parameter characteristics for the simulation have good agreement with the experimental results. By the simulation for the individual effects, the peaks around 5 MHz result from the heat generation in GaN HEMTs. The peaks below 150 kHz are considered to originate from the traps in AlGaN and GaN layers. The traps in the GaN layer generate the peaks in both Im(Y₂₂) and Im(Y₂₁), while the traps in the AlGaN layer generate peaks in only Im(Y₂₁).