Epc2014c problem

I’m planning to use the EPC2014C GaN FET for controlling infrared LED signals. The primary reason for choosing this transistor is its fast switching speed, specifically its quick rising time. However, during my experiments, I observed that when the drain voltage is set to 12V, the gate voltage is around 4.5V, but when the drain voltage is increased to 18V, the gate voltage drops to approximately 2V. I’m curious about the reasons behind this gate voltage fluctuation and reduction, and how this phenomenon might affect the EPC2014C’s fast switching performance.

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Dear Jae,
Thank you for your question. I’m EPC FAE located in Korea.
I have sent you several questions to support your inquiry, so please refer to my email to you.