Patent GB-1459455-A (GB)
Title: Electroluminescent devices
IPC: G09F13/20
Filed: 1973-12-11
Abstract: 1459455 Semiconductor devices PHILIPS ELECTRONIC AND ASSOCIATED INDUSTRIES Ltd 11 Dec 1973 57357/73 Heading H1K [Also in Divisions C4 and G5] An electroluminescent device comprises at least two simultaneously energizable electroluminescent light sources connected in series so that current of the same intensity can be simultaneously injected in each, the light flux emitted by a first source emitting light of a first wavelength being dominant when a current of intensity I 1  is injected into each source, and the flux emitted by a second source emitting light of a second wavelength being dominant when a current of intensity I 2  is injected into each source. The device allows supply to the sources by a common conductor rather than by a plurality of conductors and supplies &c. One or more of the sources may be made up of identical series connected sources. Preferably a single source is included for each desired (primary) colours enabling other colours to be obtained by mixing. The duration of pulses varies as the required current intensity and may be inversely proportional to same. The ratio may be corrected to account for contrast conditions, for example, and other operational features are discussed w.r.t. Fig. 1 (not shown), and subjective colour effects considered. The sources may be so close together as to appear as a single source. An optical system may superimpose light from the sources e.g. an enveloping cap for side-by-side sources. Sources may be stacked in decreasing wavelength order. A diode operating in the saturation mode may be of GaP doped with Zn and O and in combination with one whose flux varies, or one whose flux is directly proportional to I (e.g. GaAsP, GaAlAs, GaInP, InAlP or GaN, or indirect band gap GaP : N or SiC) may be combined with one following a different rule. One whose flux is proportional to n(n>1) may be combined with one whose flux follows a different rule. The former may be infra-red emitting GaAs<SP>1</SP> : Si covered with transparent synthetic material (e.g. epoxy resin) containing photoluminescent grains of NaYF 4  : Yb,Er. Also one source may have a strong concentration of impurities in which a low current intensity causes only radiationless recombination, and the other of smaller forbidden bandwidth with a weaker conc. of impurities in which a low I causes radiative recombination. These sources may be GaP or InP with >10<SP>16</SP> imp./cm.<SP>3</SP>, and GaAs<SP>1</SP> with imp. <10<SP>15</SP>cm.<SP>3</SP> Fig. 3 includes two superposed sources i.e. p-n junction 42, metal deposits 33, 34, the latter a transparent grid, p-n junction 38 and infra-red to visible radiating photoluminescent cap 39. The sources may have different shapes and/or active areas. Shift of the curves in Fig. 1 may be obtained by filters. Fluxes according to the Fig. 1 curves may be obtained using GaP : Zn + O obtained by liquid epitaxy (e.g. 0À1mm.<SP>2</SP> emissive suface), GaAs 1-x P x  (x being 0À80 to 0À85) doped with N and emissive surface 5 to 20 larger, and an enveloped GaAs:Si diode as above with 2 to 10 times larger emissive surface. Operating conditions for obtaining specific colour outputs are detailed. X-Y matrix displays with only one conductor/line and/column are exemplified.