Drift velocity comparison between high-electron mobility transistors and doped-channel field-effect transistors at very small dimensions

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Abstract
Drift velocity characteristics for high-electron mobility transistors (HEMT) (nondoped-channel field-effect transistors) and doped-channel metal-insulator-semiconductor-like transistors (DMT) are compared to discuss high-speed operation at very small dimensions using an electronic transport program. This ensemble Monte Carlo simulation program takes into account multisubband conduction based upon the self-consistently determined potential well. Calculated drift velocity responses are compared between the two transistors by changing the dimensions. Consequently, enhanced drift velocity characteristics due to velocity overshoot effect are confirmed for DMT. That is, the calculated saturation velocity value exceeds 2×107 cm/s for a 0.2-μm-length transistor at 77 K. This fortunate result indcates that high-speed DMT is achievable by reducing the device dimensions. The two types of devices are compared by using a two-dimensional simulator together with the obtained drift velocity versus field relationships. As a result, it is demonstrated that much better high-speed performance is expected for HEMT at reduced dimensions, e.g., 340 GHz for a 0.2-μm-gate-length HEMT and 100 GHz for a 0.2-μm-gate-length DMT, at 77 K. The peak velocity exceeds 7.5×107 cm/s for the 0.2-μm-length HEMT. In conclusion, nondoped-channel field-effect transistors, such as HEMT, promise ultra-high-speed operation.