Transferred-Electron Induced Current Instabilities in Heterojunction Bipolar Transistors

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9422538 Jalali Instabilities in current flow in semiconductors has been of interest of some time. A well known example is the technologically important Gunn effect which has been observed in direct bandgap semiconductors such as InP and GaAs in which the electric field profile of a biased n+-n-n+ diode collapses into a high field domain. This domain is swept out of the n-region in a characteristic time, t and results in current pulses of frequency f=1/t. Since the first observation of the transferred electron effect by Gunn in 1963 the devices have been successfully implemented as low noise source of microwave and millimeter-wave radiation. The similarity between the collector region of a III-V heterojunction bipolar transistor (HBT) and the drift region of a Gunn diode has motivated us to explore the Gunn-Hilsum phenomenon in bipolar transistors. Using numerical simulations, we have shown that current instabilities resulting from the transferred electron effect can be observed in modified HBT structures in which the electric field profile in the collector has been properly engineered. These results have established design criteria for a new three terminal bipolar oscillator with the potential for incorporation into existing HBT integrated circuit technology, which we shall study in the this project. The proposed device will be used as a novel spectroscopic tool in which it is possible to independently vary voltage and current flow in the region of semiconductor where stability occurs. Using this property we can apply a wide range of bias conditions to assess the applicability of the Landau-Ginzburg theory of phase transitions to describe fluctuations near oscillation threshold. ***