Extension of high f/sub T/ operation bias range for an AlInAs/InGaAs HBT

The authors report on the fabrication and characteristics of AlInAs/InGaAs HBTs (heterojunction bipolar transistors) with a base-collector structure that results in high-f/sub T/ operation over a wide range of collector bias voltage variation. This feature results in high-speed switching performance for digital circuits, where the device operating bias point varies widely due to logic swing. The fabricated device exhibited an f/sub T/-V/sub CE/ characteristic with a broad peak at around 2.2 V (V/sub BE/=1.0 V). It was found that the electron transit time t/sub B/+t/sub C/ is insensitive to external voltages. A realistic flat f/sub T/-V/sub CE/ characteristic can be obtained by reducing extrinsic delay time.<>