The influence of transit-time effects on the optimum design and maximum oscillation frequency of quantum well oscillators

A small-signal analysis of quantum-well oscillators is presented. The analysis includes the transit-time effects associated with a depleted spacer layer outside the quantum well. These transit-time effects are found to dominate device characteristics and to lead to dramatic increases in achievable negative resistance. Closed-form expressions are derived for specific negative resistance and cutoff frequency, and a universal curve relating maximum transit-time negative resistance, quantum-well current-voltage characteristics, and frequency is found. Design considerations to maximize the oscillation frequency threshold are discussed. The analysis also shows that the effective limit on the maximum oscillation frequency of practical quantum-well oscillators is determined by a combination of impedance matching constraints and minimum-achievable contact resistance.<
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