Abstract: A heterojunction bipolar transistor (HBT) has shortened electron transport time through collector region over wide range of biased conditions. The HBT is expected to exhibit enhanced high frequency characteristics. In operation under biased condition, a portion of an n-GaAs collector layer makes a depletion region. A p-GaAs base contact layer is in contact with side surface of the depletion region. Even if the collector layer remains in the n-type, the contour of band potential in conduction band of the collector depletion region is adjusted to a desired one by controlling electric potential of the base contact layer. As a result, the band potential with smooth slope is created in the collector depletion region, shortening transport time through the collector layer. The intrinsic portion of the collector layer is of the n-type so that occurrence of Kirk effect is suppressed, ensuring enhanced high frequency characteristics.

Abstract: In a bipolar transistor including a semi-insulating substrate, a collector layer formed on the semi-insulating substrate and a base layer formed on the collector layer, a base contact layer is in contact; with a part of a lower surface of the base layer.