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What role did John Bardeen play in the invention of the transistor?

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NMOS transistorNegative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors. — transistor NMOS transistor
Negative-channel metal-oxide semiconductors (NMOS) employ a positive secondary voltage to switch a shallow layer of p-type semiconductor material below the gate into n-type. For positive-channel metal-oxide semiconductors (PMOS), all these polarities are reversed. NMOS transistors are more expensive, but faster, than PMOS transistors.

John Bardeen played a pivotal role in the invention of the transistor as a theoretical physicist at Bell Laboratories.12

After previous attempts to create a solid-state amplifier failed, Bardeen provided a crucial theoretical breakthrough in March 1946. He conjectured that electrons were being trapped at the surface of the semiconductor material, creating a barrier that prevented an external electric field from influencing the conductivity of the bulk material.2

This insight led to a focused research program on "surface-state" electrons. In December 1947, working closely with experimental physicist Walter H. Brattain, Bardeen successfully utilized this understanding to invent the point-contact transistor. This device, which used two closely spaced metal wires to modulate current, served as the first successful semiconductor amplifier.12

For their joint work on the transistor, Bardeen, Brattain, and William B. Shockley were awarded the 1956 Nobel Prize for Physics.134