Semiconductor light-emitting devices including light emitting diodes (LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, one or more light emitting layers in an active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region. Electrical contacts are formed on the n- and p-type regions.
A light emitting device such as an LED is often combined with a wavelength converting material such as a phosphor. FIGS. 1A-1E are side cross-sectional views illustrating process steps needed to fabricate a wavelength conversion chip, described in more detail in US 2012/0086028. The process is described as follows in US 2012/0086028: The first step in the process for forming wavelength conversion chips is to select a substrate 100, which is shown in a side cross-sectional view in FIG. 1A. The substrate provides a physical support for the subsequent deposition of the wavelength conversion layer. Substrate 100 has a bottom surface 120 and a top surface 140 opposite bottom surface 120. Substrate 100 can be a polymeric material or an inorganic material. See, for example, paragraph 77.
The next process step is to deposit a wavelength conversion layer 200 on the top surface 140 of substrate 100 as illustrated in a side cross-sectional view in FIG. 1B. The wavelength conversion layer 200 has a bottom surface 220 in direct contact with the top surface 140 of substrate 100 and a top surface 240. The wavelength conversion layer 200 is formed from wavelength conversion materials. The wavelength conversion materials absorb light in a first wavelength range and emit light in a second wavelength range, where the light of a second wavelength range has longer wavelengths than the light of a first wavelength range. The wavelength conversion materials may be, for example, phosphor materials or quantum dot materials. The phosphor materials may be in the form of powders, ceramics, thin film solids or bulk solids. See, for example, paragraphs 78 and 79.
The next process step is an optional annealing step, as illustrated in FIG. 1C, to thermally anneal or radiation anneal 300 the wavelength conversion layer 200 in order to increase the wavelength conversion efficiency of the layer or, in the case of a phosphor powder, to sinter the powder to form a ceramic layer. See, for example, paragraph 85.
The next process step is to segment the wavelength conversion layer 200 into a plurality of wavelength conversion chips 500. Grooves or streets 400 are formed through the wavelength conversion layer 200 as shown in a side cross-sectional view in FIG. 1D. The streets 400 are fabricated in two directions (only one direction is shown) to form a plurality of wavelength conversion chips 500 that can be square, rectangular or any other planar geometric shape. See, for example, paragraph 88.
The final step is to remove the plurality of wavelength conversion chips 500 from substrate 100. For example, the plurality of wavelength conversion chips 500 can be removed by directing a pulsed laser beam 600 though substrate 100 to destroy the adhesion of the bottom surface 220 of the wavelength conversion layer 200 to the top surface 140 of the substrate 100 as shown in a side cross-sectional view in FIG. 1E. See, for example, paragraph 89.