APPLICATION

The PDB diode is a majority-carrier device. It has no minority-carrier storage and is capable of high-frequency operations. It has certain advantages over the Schottky-barrier diode. First, the barrier can be varied between zero to approximately the energy-gap value. The degree of symmetry between the forward and reverse directions can also be adjusted. Second, the barrier is not at the metal-semiconductor interface so that it is more stable in response to electrical stress. Third, since all the layers are semiconductors, the PDB structure is more flexible as a device building block. Applications of the PDB diode are listed below.

1. Referring to the energy-band diagram, if extra minority carriers (holes) are supplied by external means, they would accumulate at the peak of the valence band. These positive charges set up a field that reduces the barrier heights, resulting in a larger thermionic-emission (majority-carrier) current. This property of current gain is used in a photodetector and switch.

2. Two PDB diodes back-to-back are used to form a hot-electron transistor. The planar-doped barrier has also been incorporated as the channel or the gate of various FETs.

3. As a microwave mixer and detector, it has performance similar to that of a Schottky- barrier diode. It can also be used as a special subharmonic mixer that requires symmetrical I-V characteristics. In this case it replaces two Schottky-barrier diodes in anti-parallel.

4. It can replace the Schottky barrier as the injecting junction in a BARITT diode or a TED.