GaAs bipolar transistors grown on (100) Si substrates by molecular beam epitaxy

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Abstract
We have investigated the properties of GaAs homojunction bipolar transistors grown on (100) oriented Si substrates by molecular beam epitaxy. In a structure with a base thickness of 0.2 μm, a small‐signal common emitter current gain β of about 10 at a current density of 10 kA/cm2 has been obtained. Current densities as high as 105 000 A/cm2 were obtained in these devices without degradation demonstrating the excellent stability of this material. Since the minority‐carrier lifetime is quite sensitive to defects in the base region, these measurements demonstrate the high quality of GaAs on Si substrates. From the collector current dependence of current gain, an ideality factor n=1.5 for the emitter junction was obtained, indicating that space‐charge recombination is an important mechanism in these devices. We also demonstrate that the entire GaAs on Si wafer is phase ordered by observing the orientation effect in the mesa etching. These results show that excellent minority‐carrier properties can be obtained in GaAs on Si epitaxial layers despite the somewhat large dislocation density due to lattice mismatch.