Advanced RF enhancement-mode FETs with improved gate properties

A method for making an enhancement mode RF device, comprising the steps of:

• providing a substrate having a stack of semiconductor layers formed thereon, the stack including a doped cap layer and a central layer defining a device channel;
• depositing a dielectric layer over the cap layer;
• depositing a photoresist over the dielectric layer;
• and
• in any order, (a) forming a dielectric mask out of the dielectric layer, (b) creating an implant region, (c) selectively removing a portion of the cap layer, thereby defining a capped region and an uncapped region, and (d) removing the photoresist;
• wherein, after steps (b) and (c) are performed, the implant region and the capped region do not substantially overlap.

A method for making an enhancement mode RF device, comprising the steps of:

• providing a semiconductor construct having a first layer comprising GaAs disposed over a second layer comprising AlGaAs;
• disposing a dielectric layer on the first layer;
• forming a photoresist mask over the dielectric layer, thereby defining a first masked region and a first unmasked region, the first unmasked region including a first portion of the first layer;
• patterning a hardmask in the dielectric layer, thereby defining a second masked region and a second unmasked region, the second unmasked region including a second portion of the first layer;
• removing the photoresist;
• creating an N+ implant in the second unmasked region;
• and
• removing the first and second portions of the first layer.

A method for making an enhancement mode RF device, comprising the steps of:

• providing a substrate having a stack of semiconductor layers formed thereon, the stack including doped a cap layer and a central layer defining a device channel;
• disposing a first mask over the cap layer, thereby defining a first masked region and a first unmasked region;
• in any order, (a) creating an implant region in the first unmasked region, and (b) removing the cap layer from the first unmasked region;
• removing the first mask;
• disposing a second mask, distinct from said first mask, over the cap layer, thereby defining a second masked region and a second unmasked region;
• and
• forming a gate opening through the cap layer in the second unmasked region.