The diode is made by plating lithium onto one end of the silicon. The lithium is
drifted into, that is diffused into, the silicon crystal by an applied voltage. The high concentration
of Li at the one end creates an n-type region. In the diffusion process, all electron
acceptors are neutralized in the bulk of the crystal, which becomes highly
nonconducting. This is the “intrinsic” material. The lithium drifting is stopped before
reaching the other end of the silicon crystal, leaving a region of pure Si (p-type), as
shown in Fig. 8.30. Submicron gold layers are applied at each end as electrical contacts.
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