| Incorporating bismuth into epitaxially grown GaAs layers produces the alloy GaAs1--xBi x. This new material system shifts the band gap of GaAs down by approximately 88 meV/%Bi, while maintaining a small lattice mismatch of less than 0.25 % for a 200-300 meV band gap shift. This material has many potential applications in optical and electron devices. In this work the material is studied for use in device applications, specifically heterojunction bipolar transistors with a narrow band gap GaAsBi base layer. The performance of this device is simulated to find its maximum potential gain and frequency of operation in the X-band at devices sizes of 0.5 mum for < 2.5 % bismuth alloying. P-N and HBT devices are fabricated to characterize material quality and HBT performance. Loss mechanisms are studied to improve future devices in the GaAsBi material system. |
