MBE GROWTH OF QUATERNARY INGAALAS LAYERS IN INGAAS INALAS HBTS TO IMPROVE DEVICE PERFORMANCE/

InAlAs/InGaAs HBTs grown on InP substrates can achieve excellent high- frequency performance but suffer from low breakdown and low current ga in due to the small InGaAs bandgap. By replacing the InGaAs collector and/or base with a quaternary InGaAlAs layer the device characteristic s are improved. Using an InGaAlAs collector the breakdown voltage is f ound to increase the breakdown voltage of the device from 15 to 23 V. Using such a layer in both the collector and base has the added benefi t of increasing the device current gain from 40 to greater than 60. Cu rrent gain can be increased even more dramatically to 88 by using a gr aded InGaAlAs layer in the base. However, the use of InGaAlAs layers w as found to increase the device V-be voltage and degrade the RF proper ties somewhat. These parameters can be traded off and optimized for a given application.