III-V compound semiconductor device with a surface layer in access regions having charge of polarity opposite to channel charge and method of making the same

A method of forming a III-V compound semiconductor structure, comprising:

• providing a III-V compound semiconductor substrate including a semi-insulating substrate having at least one epitaxial layer formed thereon, and further having a gate insulator overlying the at least one epitaxial layer, wherein the at least one epitaxial layer formed on the semi-insulating substrate comprises an epi-structure suitable for use in the formation of a channel of a III-V compound semiconductor MOSFET device, the channel having a first polarity;
• forming a charge layer at a surface of the gate insulator, the charge layer having a second polarity, wherein the second polarity is opposite to the first polarity;
• forming source and drain contacts, wherein the source and drain contacts extend from the surface of the compound semiconductor structure and into the epi-structure, wherein forming the source and drain contacts defines a channel region within the epi-structure between the source and drain contacts;
• and
• forming a gate contact overlying the gate insulator and positioned between a location of the source and drain contacts, wherein forming the gate contact includes forming the gate contact in a gate region, further in the absence of the charge layer at the surface of the gate insulator underlying the gate contact in the gate region, wherein a portion of the charge layer at the surface of the gate insulator remains in access regions defined by a first access region extending between the source contact and the gate contact and a second access region extending between the drain contact and the gate contact,
• wherein the gate region includes the gate contact overlying the gate insulator in the absence of the charge layer at the surface underlying the gate contact, the gate region further extending from the gate contact and into a portion of the channel underlying the gate contact,
• wherein the first access region further extends from the charge layer at the surface of the gate insulator in the first access region and into a portion of the channel underlying the first access region between the source contact and the gate contact,
• wherein the second access region further extends between the drain contact and the gate contact at the surface of the gate insulator in the second access region and into a portion of the channel underlying the second access region between the drain contact and the gate contact, and
• wherein the charge layer in the access regions decouples a charge density in the portion of the channel in the access regions from a charge density in the portion of the channel in the gate region.