Patent GB-1100682-A (GB)
Title: Improvements in opto-electronic semiconductor devices
Inventor: BEALE JULIAN ROBERT ANTHONY
IPC: H01L21/00
Filed: 1963-09-26
Abstract: 1,100,682. Semi-conductor devices. MULLARD Ltd. 6 Aug., 1964 [26 Sept., 1963], No. 37947/63. Heading HIK. In an opto-electronic semi-conductor device comprising four layers of alternate conductivity types, the junction between the first and second layers emits photons when forwardly biased and the minimum separation between this junction and the junction between the second and third layers is greater than a minority carrier diffusion length. As shown, Fig. 5, a wafer 11 of N-type GaAs doped with tellurium, has P-type surface layers 12, 13 produced by diffusing-in zinc. The thickness of layer 12 is reduced by etching and part of the new surface is masked and the exposed part of layer 12 is removed. Layer 13 is also reduced in thickness by etching, and pellets 14, 16 of bismuth-tin-platinum alloy are alloyed to regions 13 and 11 to form a rectifying and an ohmic connection respectively. A pellet 16 of bismuth-cadmium alloy is alloyed to region 12 to form an ohmic contact. A reflective coating 17 of aluminium is applied over contact 16 and layer 12, leads are attached to the alloyed contacts and the device is encapsulated. Layers 12, 11, 13 act as an opto-electronic transistor in which recombination radiation emitted by the forward biased junction between layers 11 and 12 produces electron-hole pairs at the reverse biased junction between layers 11 and 13. Layers 14, 13, 11 act as a junction transistor and if the sum of the current amplification factors of the two " transistors " exceeds unity the complete device operates as a high speed switch controlled by gate contact 15. In a second embodiment, Fig. 8, an N-type wafer of GaAs doped with tellurium and having P-type surface layers produced by vapour diffusion of zinc is attached to a glass plate using dental wax and the exposed P-type layer removed by grinding and etching. The wafer is reversed on the plate and the remaining P-type layer is reduced in thickness using the same method. The wafer is then divided into a plurality of wafers 22 and an annular cavity 24 is ultrasonically drilled through the P-type layer 23 of each wafer. A pellet 25 of bismuthtin alloy is alloyed to the wafer to form a rectifying contact and a ring 26 of bismuthsilver alloy and a pellet 27 of bismuth-tinplatinum alloy are alloyed to the wafer to form ohmic contacts. A silicon oxide layer 29 and a reflective layer 30 of aluminium are applied to the edges of the wafer. Leads are connected and the device encapsulated, cavity 24 being filled with a transparent lacquer through which the light emitted from the outer annular junction can pass to the co-planar inner junction. This device operates as in the first embodiment. The light receiving junction may also be a heterojunction, the material of the third region having a lower energy gap than that of the second region to decrease the photon absorption length. Suitable pairs of materials are gallium arsenide/gallium-indium arsenide and gallium arseno-phosphide/gallium arsenide. In a preferred embodiment the first and second regions are of the first material and the third and fourth regions are of the second material. Reference has been directed by the Comptroller to Specification 967,439.