HIGH-FREQUENCY SIMULATION OF SEMICONDUCTOR ALLOY RAMP HETEROSTRUCTURES

A small-signal ac transport description is formulated to characterize the high-frequency operation of unipolar semiconductor heterostructures. The physical transport model combines diffusion-drift currents through compositionally graded regions with a thermionic-emission current imposed at an abrupt material interface. This sinusoidal steady-state analysis can be employed to determine the dynamic terminal admittance of devices at microwave frequencies and cryogenic temperatures. AlxGa1-xAs alloy ramp heterostructures have been fabricated by molecular beam epitaxy and tested over wide ranges of temperature, dc bias, and frequency. Experimentally measured microwave admittances are favorably compared with simulated results at room and liquid-nitrogen temperatures, and are used to verify the theoretical approach.