Antimony-based quaternary alloys for high-speed low-power electronic devices

Heterojunction bipolar transistors using In_zGa_1-zSb for the base and In_xAl_1-xAs_ySb_1-y alloys for the collector and emitter have been explored. Modeling of the DC current-voltage characteristics indicate that current gain in excess of 500 may be obtained. The calculations show that the gain is a function of the base-collector conduction band offset. Molecular beam epitaxy (MBE) procedures for growing suitable alloys with a 6.2 Å lattice constant are under development. Double crystal X-ray diffraction, photoluminescence, Hall effect, and atomic force microscopy have been used to determine the quality of the materials grown. To minimize stress-induced defects, the In_xAl_1-xAs_ySb_1-y alloys were grown on undoped GaSb substrates with an AlSb buffer layer. The photoluminescence data indicate that good quality In_xAl_1-xAs_ySb_1-y (x=0.52 and y=0.3) with a band gap near 1 eV, is obtained using growth temperatures between 350 and 400°C. Superior surface morphology is also found for growths in this temperature range. Te has been used to dope In_xAl_1-xAs_ySb_1-y n-type in the 10¹⁷ cm^-3 range. Good diode characteristics with an ideality factor of 1.1 have been obtained for In_xAl_1-xAs_ySb_1-y p-n junctions grown using Te for the n-type dopant and Be for the p-type.