Chushirou Kusano

The Effect on Turn-On Voltage (VBE) of AlGaAs/GaAs HBT's due to the Structure of the Emitter-Base Heterojunction

The effects on the turn-on voltage (VBE) of collector current in AlGaAs/GaAs HBTs due to Be diffusion and discontinuity in the conduction band are investigated. It is clarified that VBE increases significantly with the decrease in saturation current due to Be diffusion into the AlGaAs emitter during MBE growth. It is also found that the VBEs of HBTs with Al compositionally abrupt and graded emitter-base junctions and homojunction GaAs bipolar transistors are the same. These results indicate that the spike-like potential barrier at the heterojunction has no influence on the electron injection from emitter to base.

AlGaAs/GaAs HBTs for 10-Gb/s ICs using a new base ohmic contact fabrication process

A new basic ohmic contact technology for AlGaAs/GaAs heterojunction bipolar transistors (HBTs) is presented. The effect of the device parameters on the high-frequency performance of HBT ICs for 10-Gb/s systems is analyzed, and it is shown that, at a cutoff frequency (f/sub T/) of 40 GHz or more, reducing base resistance or collector capacitance is more effective than increasing f/sub T/ for obtaining high-frequency performance. A process is developed for fabricating base electrodes with a very low ohmic contact resistivity, approximately 10/sup -7/ Omega -cm/sup 2/, by using a AuZn/Mo/Au alloy, which provides the required high performance. Self-aligned AlGaAs/GaAs HBTs, with a 2.5- mu m*5- mu m emitter, using a AuZn/Mo/Au alloy base metal and an undoped GaAs collector, are shown to have an f/sub T/ and a maximum oscillation frequency of about 45 and 70 GHz, respectively, at 3.5 mA. An AGC amplifier with a 20-dB gain and a bandwidth of 13.7 GHz demonstrates stable performance. >