Fabrication of double recess structure by single lithography step using silicon-nitride-assisted process in pseudomorphic HEMTs

• A new fabrication process of double recess structure using single masking.
• Any recess widths and heights can be realized with a single lithography step.
• Double recess structure achieved by varying silicon nitride and GaAs etch times.
• Electric field simulation substantiates tailoring of the electric field.
• Led to increased breakdown voltages essential for power applications in pHEMTs.

Monolithic microwave integrated circuits (MMICs) play an important part in today’s wireless communication electronics. GaAs-based pseudomorphic High Electron Mobility Transistor (pHEMT) is used in MMIC-based low noise amplifier (LNA) and power amplifier (PA) stages. The latter requires high device current (Ids) and high reverse breakdown voltage (BVgd). In addition, the ON-state breakdown voltage should be high enough to operate the device at higher source–drain voltage (Vds). Double gate recessing is a well-established technique used to increase the ON and OFF-state breakdown voltages of a pHEMT device for power applications, which requires two levels of masking and recessing. In this paper, we present a single mask processing technique for realizing double recess structure with the help of silicon nitride layer. The new process involves deposition of silicon nitride after mesa isolation step of device fabrication. After gate lithography, two etching steps of silicon nitride and GaAs, followed one after the other, generates the double recess structure, wherein the various etch times decide the width and shape of double recess structure. The electric field distribution at the Schottky interface as well as along the channel has been simulated using ATLAS for the double recess structure used in this work. The fabricated recess structure showed improvement in breakdown voltage of the device which has been correlated to the effective redistribution of electric field in the device, as shown by simulation.

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