The non-crystalline stute silicon is used as emitter material for bipolar microwave power transistor. By means of the ballast effect of the vertical resistor of this non-crystalline Si layer

inject current crowding at emitter edge can be overcome. The ratio of effectual emitter area to base area of a FFJ is 2-3 times greater than a usual transistor and the output power-impedance product is 5-10 times greater.The emitter-base junction capacitance of the FFJ is only decided by it’s emitter doping profiles

so that both smaller base resistance rb and higher emitter cutoff frequency can simultaneously be obtained. The value of fmax is 3-5 times greater than the usual transistor.