The ever expanding use of semiconductor light emitting devices has produced a highly competitive market for these devices. In this market, performance and price are often significant for providing product distinction among vendors.
Side-emitting LEDs are commonly used in applications requiring a low profile device and a dispersed light pattern, such as backlighted display panels, and thin troffers for general illumination. FIGS. 1A-1C illustrate a conventional technique for providing a side-emitting device, such as disclosed in U.S. Pat. No. 8,109,644, issued 7 Feb. 2012 to Serge Bierhuizen, and incorporated by reference herein.
FIG. 1A illustrates a substrate 110, upon which semiconductor layers are formed/grown to create multiple light emitting elements 120. The substrate 110 is commonly sapphire, SiC or GaN, and the light emitting element 120 is commonly an active region sandwiched between an n-type semiconductor layer and a p-type semiconductor layer. Pads 130 provide contact to the n and p layers, such that when current flows between these layers, light is emitted from the active region. Gallium nitride (GaN), doped to provide the n-type and p-type semiconductors, is commonly used as the semiconductor forming the light emitting element 120.
The substrate 110 may be sliced/diced to provide singular light emitting chips, which may be subsequently placed on another substrate 140, commonly termed a submount, in a ‘flip-chip’ orientation (pads 130 being on the ‘bottom’ of the chip), as illustrated in FIG. 1B. The pads 130 are coupled to contacts 145 on the submount 140 to allow for external electrical connection to the light emitting element 120. With the submount providing structural support to the light emitting element 120, the substrate 110 may be removed.
To provide a desired color point (hue and color temperature), a wavelength conversion element 150 is placed upon the light emitting surface 125 of the light emitting element 120, to provide a light emitting device 100 as illustrated in FIG. 1C. The wavelength conversion element may contain one or more wavelength conversion materials, such as phosphors. To provide side emissions, a reflector 160 is situated above the wavelength conversion element 150, so that the light is emitted through the sidewalls 155 of the wavelength conversion element 150. The reflector 160 may be a specular reflector or a diffusing reflector.
In some embodiments, light is emitted from all sidewalls of the wavelength conversion element 150; in other embodiments, one or more of the sidewalls of the wavelength conversion element 150 may be reflective, thereby causing the light to be emitted from the remaining non-reflective sidewall(s) 155. Optionally, one or more optical elements, such as collimators, may be used to further direct the side-emitted light in a desired direction.
Generally, the wavelength conversion element 150 is attached to the light emitting element 120 soon after the substrate 110 is removed, to protect the light emitting surface 115. Accordingly, the choice of a wavelength conversion element 150 having particular characteristics is generally made prior to the manufacture of the device 100.