<p>1487024 Light emitting diodes NORTHERN TELECOM Ltd 13 Aug 1975 [10 Sept 1974] 33788/75 Heading H1K [Also in Division C4] A double hetrostructure LED has at least one convex lens 29 on its surface projecting into a aperture 35 into substrate 20. The device is formed by etching hole 23 in the substrate 20 through a photoresist layer 21 or a SiO 2 mask. The layer or mask is removed and a 4 layer LED 24 is grown. The first layer 25 fills the hole and provides lens 29 when the aperture is formed in the substrate. Layer 25 may contain a plurality of lenses formed using a pluralty of holes 23. The substrate is of GaAs and the layers are of GaAlAsP : Te; GaALAs : Si; GaAlAs : P; and GaAs : Ge. Current may be confined to the portions of the LED under the centres of the lenses.</p>
