Patent GB-1426956-A (GB)
Title: Electroluminescent device
IPC: H01L31/14
Filed: 1973-03-09
Abstract: 1426956 Electroluminescence PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 9 March 1973 [14 March 1972] 11415/73 Heading C4S [Also in Division H1] An electroluminescent device comprises surface region 5 forming a light emitting P-N junction 6 with second conductivity type region 4, photoconductive layer 2 of semi-insulating material having a forbidden bandwidth smaller than the electroluminescent photons, the photoconductive layer being optically isolated from the P-N junction by an absorbing layer 3 having a forbidden bandwidth between that of the photoconductive layer and the EL photons, the photoconductive and absorbing layers being of the second conductivity type. "Semiinsulating" is defined as a s./c. material whose conductivity type doping is partially compensated by defects of the crystal lattice or deep level impurity doping so that the resistivity is 10<SP>2</SP> to 10<SP>8</SP> # cm. The EL brightness may be controlled by auxiliary radiation and control of contrast with varying ambient light in vehicles and airplanes using the photo-electric component is discussed. Materials may comprise one or more of Ga, In and Al, and one or more of As and P. Al and Ga cones. in epitaxial Ga 1-x Al x As (0<x<0À40) may control forbidden bandwidths, e.g. in the P region 5 and N region 4 where 0À3<x<0À4, in layer 3 where 0<x<0À3, layer 2 being s.i. GaAs. An intermediate buffer zone of gradually varying composition may be included and may be at least partly the absorbing layer and may extend into p/c layer 2. Regions 5 and 4 may be GaAs 1-x P x  where 0<x<0À4, x decreasing through the absorbing layer to 0 in the p./c. layer and the Si layer being of gallium arsenide. Corresponding details are given for Ga x In 1-x P (x=0À25) . The photoconductive layer may be formed by partial doping with Cu, Mn, Fe, Ni or Co (10<SP>2</SP>-10<SP>5</SP> # cm.) or with Cr or O (10<SP>5</SP>-10<SP>8</SP> # cm.) The electrode on the emitting surface may be transparent or apertured, e.g. a ring or grid. Fig. 1 includes N-type GaAs substrate 1, N GaAs component 2 partially Cu compensated, N component 3 with an additional GaP context increasing (e.g. to 40%) towards region 4, the latter being N-type GaAsP and including P region 5. The emissive surface and possibly the junction may be convex, e.g. spherical. Fig. 4 (not shown) uses a Weierstrass' spherical geometry to reduce reflection losses. Strongly doped layer (41) of the same conductivity type as layers (45, 43, 42) ensure non-rectifying ohmic contact with opaque electrode (40). Again, radiation enters and exits from the same surface. Fig. 5 (not shown) has both electrodes on the radiation input-output face and includes low resistivity plate (61), and p./c. semi-insulating region (62). Fig. 6 (not shown) includes a plurality of junctions with a common electrode. The substrate may be a 150 Á thick disc of GaAs with 5.10<SP>17</SP> Te atoms/c.c., a 10 Á layer of GaAs compensated with Cu to a 10<SP>3</SP> to 10<SP>4</SP> # cm. resistivity epitaxially deposited from a vapour phase, and  subsequently a P compound gradually added to  the reactor with Se or Te doping to produce a 20 Á buffer layer of final composition GaAs 0À61 - P 0À39 . A 10 Á layer with constant P content is subsequently diffused with 10<SP>19</SP> Zn atoms/c.c. to 5 Á. Vacuum deposited electrodes are Al and Sn. Insulator (87) reaches at least layer (83) and preferably substrate (81). SiO 2 , Si 3 N 4 , epoxy resins or isolation diffusions of reverse polarized P-N junctions are mentioned. Photo-electric, and ion implantation techniques are also disclosed and relative areas of the layers. Applications also include α-numeric or X-Y matrix signal or indicator lights.