This application is a division of U.S. application Ser. No. 17/955,526, filed on Sep. 28, 2022, which is a continuation application of U.S. application Ser. No. 17/148,539, filed on Jan. 13, 2021. The contents of these applications are incorporated herein by reference.

The present invention relates to the field of semiconductor devices, and more particularly to high electron mobility transistors and fabricating method thereof.

In semiconductor technology, group III-V semiconductor compounds may be used to form various integrated circuit (IC) devices, such as high power field-effect transistors (FETs), high frequency transistors, or high electron mobility transistors (HEMTs). A HEMT is a field effect transistor having a two dimensional electron gas (2-DEG) layer close to a junction between two materials with different band gaps (i.e., a heterojunction). The 2-DEG layer is used as the transistor channel instead of a doped region, as is generally the case for metal oxide semiconductor field effect transistors (MOSFETs). Compared with MOSFETs, HEMTs have a number of attractive properties such as high electron mobility and the ability to transmit signals at high frequencies. However, there is still a need to improve the breakdown voltage (V_BR) of conventional HEMTs in order to meet the requirements of the industry.

In view of this, it is necessary to provide an improved high electron mobility transistor so as to meet the requirements of the industry.