| 摘要 |
1,201,428. Electroluminescence. GENERAL ELECTRIC CO. 22 Oct., 1968 [24 Nov., 1967], No. 50128/68. Heading C4S. [Also in Divisions H1 and H5] A SiC electroluminescent PN junction diode comprises a SiC crystal the bulk of which is N-type containing a donor; the crystal has a diffused region next to one surface in which the donor concentration decreases towards the surface and an acceptor concentration which is greater than the donor concentration at the surface decreases inwardly from the surface, the concentrations being such that at the junction the donor and acceptor concentrations have substantial gradients in opposite directions. The diodes are grown by diffusing B and Al into N-doped α-SiC crystals. Concentrations and gradients are specified. Polished crystals 1b separated by porous graphite spacers 15 are placed in a graphite crucible 7 having dense and porous outer and inner walls 12, 13. The space between the walls is filled with a protective charge 14 of Si and C powder mixed with Al and B dopants, the B dopant may be boric acid. The crucible is heated in a graphite resistance furnace (see Division H5) in an argon stream at 1300‹, 1450‹ and 1600‹ C., each for 1 hour, then at the diffusion temperature, preferably 2200‹ C. At 1300‹ C. N diffuses out of the crystals, at 1450‹ C. the protective charge reacts to form SiC containing uniformly distributed B and Al. At 1600‹ C. further outgassing of the furnace and charge occurs. At 2200‹ C. the protective charge maintains a vapour pressure in the inner chamber which prevents dissociation of the SiC crytals whilst allowing B and Al to diffuse in and N to diffuse out, the surface concentrations of N, B and Al becoming equal to that in the charge. The charge may be reused and be of SiC initially. The crystals have a P-type layer on both sides, one of which is removed by grinding, then they are cut into square elements. A dispersion of Al in an organic solution containing Si is applied to the P-layer and heated to form a layer of Al-Si eutectic whilst a Au-Ta alloy contact is fused to the N-layer. The P-layer of the element is soldered or cemented using a Au-epoxy resin to a Au-plated metal base-plate of a transistor type header. A gold wire is bonded to the Au-Ta contact, alternatively Fe or NiCr alloy wire is fused to the N-layer. The header is enclosed by a metal cover with a lens or an all glass cap. |
