Patent GB-1323454-A (GB)
Title: Electroluminescent device
IPC: H01L21/00
Filed: 1970-08-13
Abstract: 1323454 Semi-conductor devices INTEL CORP 13 Aug 1970 [21 Aug 1969] 39135/70 Heading H1K [Also in Division C4] A solid state EL device includes a body of low resistivity wide band gap semi-conductor material comprising N-type ZnS having a donor density sufficient to reduce its resistivity below 100 # cm. and containing deep luminescent recombination centres, the body having a first surface region 102 treated to provide # 10<SP>17</SP>cm._<SP>3</SP> of donor atoms for injection of majority charge carriers from a first ohmic contact electrode, and a second surface region 104, treated to provide injection of minority charge carriers from a second contact electrode and including a compensated semi-insulating layer of thickness <1 Á, preferably <1000 , and including the above concentration of donor atoms and at least the same concentration of acceptor atoms (e.g. #10<SP>18</SP> cm.<SP>-3</SP>) for injection of minority charge carriers into the second region, the device being such that when biased to cause majority charge carriers to be injected into the body of the device via the first region, majority charge carriers entering the second region create a local space charge such as to enable injection of minority charge carriers from the second electrode into the second region and limit the flow of majority carriers through the second region from the body of the device whereby majority carriers and minority carriers entering the second region can combine at the recombination centres and emit photons. The ZnS material has as luminescent activator impurity constituting the recombination centres a Group I metal or a halogen or a Group III metal either alone or in combination. Acceptors may be Ag or Cu, or a mixture of Ag and Cu or a compound of Ag or Cu. The electrodes 108, 106 may have electronegativities respectively of less than and at least 1À8 eV on the Pauling Scale, e.g. In, Al, Mg or Au, Pt, Pd, Ag, Cu. The recombination centres may be between 0À5 eV and 1À5 eV of the valence band edge. For red, green and blue emission photons of respective energies of 1À8 eV, 2À3 eV and 2À8 eV are required. Operational features, band gaps and many other features are discussed in relation to the figures and Fig. 6 (not shown) illustrates T-V curves for a metal- ZnS interface barrier and Fig. 7 (not shown) a set of capacitance voltage curves. Reference is also made to devices including Group I metals such as Au when alone or in combination with halogens, e.g. Cl, Br or I or a Group III metal, e.g. Ga, In and Al, also the formation of complex or compensated states with each other or localized level formations by self-compensation with a defect such as S or Zn vacancy. Considerable fabrication details are disclosed and also specific dimensions, dopant concentrations, operational voltages and resistivities. For example, a slice of Al doped N-type ZnS may be treated in liquid Zn at 800 C. for 20 mins. to introduce Zn atoms into the crystal to fill Zn vacancies thus reducing the resistivity. Treatment may also be in Zn containing vapour. The thin semi-insulating hole injecting layer is provided on one cleaved surface by either (a) evaporating a film of Ag approx. 100  thick on to the surface, heating at about 700 C. for 10 secs. in an Ar atmosphere containing some S, (b) evaporating a Ag film approx. 1000  thick on the surface, heating as in (a) in an Ar atmosphere, and removing any remaining Ag with HNO 3 , (c) applying a thin layer of silver sulphide and heating as in (b). Au dots are evaporated to complete the contact. The ohmic electron injecting contact is formed on the back surface by first etching with HCl, then scrubbing with In-Hg amalgam to set the surface. A preformed slug of slightly Cd-rich Cd-In alloy is pressed on to the surface and the slice heated for 1 min at 350-450 C. in Ar. Other variations are disclosed. In modifications, to change the emitted light from blue towards green, a layer of copper sulphide is either added on top of or replaces the Ag doped layer. Reference is made to production procedure in Specification 1,304,593. Reference is made to multicolour displays producing different colours in the red to yellow to green to blue regions. The devices may be incorporated in logical or functional circuitry and in an array to provide a digital display of complex images.