MICROWAVE PERFORMANCES OF N-P-N AND P-N-P ALGAAS/GAAS HETEROJUNCTION BIPOLAR-TRANSISTORS

The performance of metalorganic chemical-vapor-deposition (MOCVD)-grown n-p-n and p-n-p AlGaAs/GaAs heterojunction bipolar transistors were compared at microwave frequencies to identify the relative merits of each type of device. The ft and fmax values of devices with 100-nm-thick bases were 22 and 40 GHz for n-p-n transistors and 19 and 25 GHz for p-n-p transistors, respectively. An accurate device model was developed using the measured S-parameter data. The base resistance of the p-n-p transistors, as determined from the model, was about six times lower than that of identical size n-p-n devices. Output-power and power-added efficiencies of p-n-p devices were found to be half those obtained with n-p-n devices at 10 GHz.