IMPROVEMENTS IN OR RELATING TO IMPATT DIODES

摘要

1,236,157. Semi-conductor devices. FUJITSU Ltd. 17 Oct., 1969 [17 Oct., 1968], No. 51219/69. Heading H1K. An IMPATT diode comprises a high resistivity epitaxial layer of one conductivity type on the surface of a low resistivity substrate of the opposite conductivity type, a diffused region of said opposite conductivity type extending through the epitaxial layer, and a diffused region of said one conductivity type extending across the first diffused region at the surface of the epitaxial layer to define an active junction area between the two diffused regions having a lower breakdown voltage than the junction area between the epitaxial layer and the substrate. As shown Fig. 1, a P type Si epitaxial layer 2 doped with B is deposited on an N+type substrate 1 doped with Sb. P is diffused-in to form N type region 3 and B is then diffused-in to form a P type region 4. The resulting junction ABCDEF has a lower breakdown voltage over the active region CD than over the regions AB and DF so that the avalanche occurs in the centre of the device. The edge of the wafer may be provided with a protective layer (not shown) e.g. of silicon oxide, to passivate the junction. The active part of the structure may have a P+NN+ or P+NIN+ structure depending on the impurity concentration profile. N+PP+ and N+PIP+ structures may also be produced and the semi-conductor material used may be Ge or a III-V compound such as GaAs instead of Si. The diode (10) may be inverted and mounted with the surface of the epitaxial layer (2) in contact with a pedestal on a gold-plated copper heat sink (5) so that the heat generated at junction part CD is readily dissipated Fig. 2 (not shown). The pedestal and diode are surrounded by a ceramic tube (7) secured to the heat sink (5) and closed with a metal disc 9 to which the substrate (1) of the diode is connected by means of a gold ribbon lead (11).