Patent GB-1450433-A (GB)
Title: Light detecting and emitting junction diodes
IPC: H01L29/861
Filed: 1973-12-12
Abstract: 1450433 Light emitting and detecting junction diodes WESTERN ELECTRIC CO Inc 12 Dec 1973 [15 Dec 1972 23 July 1973] 57686/73 Heading H1K A junction diode, e.g. for infra-red light detection and emission comprises a crystalline CdSnP 2  epitaxial layer on a substrate of a monocrystal of p-type InP forming a strain-free heterojunction with the body; with electrodes providing electrical connections through the crystalline body, the junction, and the substrate in series. For detection of infra-red modulated coherent light, e.g. from a laser the beam is incident (Fig. 1 not shown) on a face of a p-type transparent InP substrate separated by a heterojunction on the other face on an epitaxial layer of n-type CdSnP 2 , and a photovoltaic response is derived from a diffused electrode of the substrate and a soldered, e.g. In electrode of the layer in series with a load resistor and a D.C. source shunted by a capacitor. The element is held in a temperature controlled enclosure. Typical currentvoltage and quantum efficiency-wavelength characteristics are given (Figs. 2, 3 not shown). In fabrication a substrate 43 is cut with (100) axis normal to the layer face from a Zn or Cd doped p-type InP crystal which, is grown by gradient freezing, zone melting, or CZOCHRALSKI pulling, divided and polished. Then it is dovetail slotted (Fig. 4A) into a plug 42 of a carbon crucible sealed into an evacuated quartz ampoule 41; the crucible containing a melted dilute solution of Cd and P in metallic Sn and being placed in a tipping furnace. The temperature is raised and held to homogenize the melt; after which the temperature is lowered and the furnace tipped (Fig. 4B) to bring solution 44 into contact with substrate 43; after which it is slowly cooled to induce epitaxial deposition. Thereafter the substrate is separated from the adherent melt by heated mercury extraction and cleaned by etching in HF + HNO3 and polished in Br + methanol. The crystal is then cleaved along (110) planes into plural diodes. Contacts of In are soldered to the CdSnP 2  layer and ohmic contact to the substrate is effected by a In + Zn eutectic or Au + Zn wire. In a modification (Figs. 5A, 5B) substrate 43 is dovetailed into a lateral wall of plug 42 of vitreous carbon crucible 46 in quartz ampoule 41 and baffled from the vapour of solution 44 by extension 47 of the plug. The substance of the solution is prepared by premelting Cd, Sn and P and the dopant in an evacuated quartz ampoule 41, air quenching, and transferring the intimate mixture of small crystals to crucible 46 where it is heated to melting point for a short time to homogenise it. Ampoule 41 is evacuated, helium filled, and sealed. After melting and tipping the solution flows past the substrate through drain holes 48, 49 into the vacant part of the ampoule. Then the melt and substrate are slowly cooled in the furnace and removed to complete its cooling in air; after which the coated substrate is separated as described. P dopants Zn or Cd enter the CdSnP 2  layer during processing. Quantum efficiency - absolute temperature characteristic is given (Fig. 6 not shown) for light emission. After processing the coated substrate is removed, cleaned, and diced and the electrodes are applied as described, and the element is excited from a D.C. source (Fig. 7 not shown) to exit light through the InP substrate.