Dependence of base built-in field for InAlAs/InGaAs HBT characteristics

This paper presents the dependence of current gain on base built-in field for npn InAlAs/InGaAs HBTs in a wide field range (0-50 kV/cm) from 300 K to 77 K. Current gain increases with increasing base built-in field up to 30 kV/cm, and then decreases at higher field. These results were analyzed by taking into account the electron transfer between Γ-L valleys, and respective recombination process. A semi-quantitative agreement with experiments was obtained. Increase in the current gain at lower field is understood considering the acceleration of electron by the built-in field and decrease at higher field is due to low velocity of electrons transferred to L valley.