The Forward Characteristic of the PIN Diode

In some diode applications it is desirable to have a very low ohmic resistance as well as a high reverse breakdown voltage. A device meeting these requirements, in which the resistance is low because of heavily doped P+ and N+ contacts and the breakdown voltage is high because of a lightly doped layer between the contacts, has been described by M. B. Prince. The device is shown schematically in Figure la and consists of three regions, the P"1" contact, the middle 1J layer, and the N+ contact . The device is called a PIN diode because the density P of uncompensated acceptors in the middle region is much less than P+ or N+ and in normal forward operation much less than the injected carrier density.2 We shall let the edge of the P P junction in the middle region be x = 0, and the edge of the PN+ junction in the middle region be x = w. Thus the region 0 ^ x ^ w is space charge neutral and bounded at each end by space charge regions whose width is of the order of the Debye length 1 Prince, M. B., Diffused p-n Junction Silicon Rectifiers, B.S.T.J., page 661 of 2 this issue. A device with similar geometry has been discussed l>y R. N. Hall, Proc. I.R.E., 40, p. 1512, 1952.