Patent GB-1087268-A (GB)
Title: A method of producing an homogeneous monocrystal
IPC: H01S5/30
Filed: 1964-11-23
Abstract: An homogeneous monocrystal of controlled composition for use in producing spontaneous and stimulated emission at controlled wavelengths comprises one element from Group IIIB of Mendeleef's Periodic Classification of the elements and two elements (one of which is either nitrogen, phosphorus or arsenic) from Group VB of the Classification.  The crystal may have the composition In (AsxPxx) where 0<x <1.  The crystal is produced by placing a monocrystalline substrate cut along a crystallographic plane and having a lattice spacing similar to that of the monocrystal to be produced, together with ingots containing the selected elements in a chamber containing a halogen atmosphere, e.g. iodine, heating and maintaining the chamber at a temperature between 750 DEG  and 900 DEG  C., the temperature of the substrate being maintained higher than that of the ingots during a first time interval to clean the substrate and the temperature gradient being reversed during a second time interval to transport the elements in a vapour phase and form the monocrystal on the substrate.  The ratio of the elements in the crystal may be determined by the ratio of the areas of the exposed surfaces of the ingots facing the substrate.  The crystal may be simultaneously doped as it is grown by inclusion of doping material, e.g. tellurium, selenium, silicon, germanium or gallium in the chamber.  The dopant may be present as free material in the chamber or the monocrystal may be grown from a pair of source crystals one of which has been previously doped to a known extent. In ex-examples diodes fabricated from monocrystals of varying composition are compared as to their spontaneous emission and stimulated emission and stimulated emission properties at various current densities.  Laser action is demonstrated.ALSO:<PICT:1087268/C1/1> A method of producing an homogeneous monocrystal of controlled composition comprising one element from Group IIIB of Mendeleef's Periodic Classification of the Elements and two elements (one of which is either nitrogen, phosphorus or arsenic) from Group VB of the Classification, comprises placing a monocrystalline substrate cut along a crystallographic plane and having a lattice spacing similar to that of the moncrystal to be produced, together with ingots containing the selected elements, in a chamber containing a halogen atmosphere, e.g. iodine, heating and maintaining the chamber at a temperature between 750 DEG C. and 900 DEG  C., controlling the temperature of the chamber during a first time interval so that the substrate is at a higher temperature than the ingots whereby the surfaces of the substrate are etched and spurious reaction products are prevented from being deposited therein and, controlling the temperature during a record time interval so that the ingots are at a higher temperature than the substrate whereby the selected elements are transported in a vapour phase and condensed on the substrate to produce the homogeneous crystal.  The crystal may have the composition In(AsxP1-x) where 0<x<1. The ratio of the elements in the crystal may be determined by the ratio of th areas of the exposed surfaces of the ingots facing the substrate. The ingots may be InAs and InP and preferably have polished surfaces. The crystal may be simultareously doped as it is grown by inclusion of doping material, e.g. tellurium selenium, silicon, germanium or gallium in the chamber.  The dopant may be present as free material in the chamber or the mono-crystal may be grown from a pair of scourse crystals one of which has been previously doped to a known extent.  In a preferred embodiment, Fig. 2, a quartz chamber 10 has flat floor 12, and metallic blocks 18 and 20 which act as heat sinks are spaced beneath the floor.  Transparent end wall 14 provides a viewing window and the other end of the chamber is initially open to permit materials to be inserted.  The heat sinks 18 and 20 are provided with apertures 22 to permit circulation of a coolant, e.g. air, and with thermocouples 28 and 30. Cut and polished substrate 32, e.g. InAs, and ingots 34 are placed above heat sinks 18 and 22 respectively, the evacuated chamber is filled with iodine and the quartz chamber is heated by being situated in a clam shell furnace.  The relative temperatures of the ingots and substrate are controlled by the circulation of coolant.  During the second time interval the ingots are substantially at the chamber temperature and the substrate temperature is reduced until a condensate appears thereon. Thereafter the substrate is maintained at a temperature slightly above the temperature at which the condensate disappears until the monocrystal is grown.  During growth the relative temprature of the monocrystal and substrate may be adjusted to maintain a uniform glassy appearance of the monocrystal.