Light-emitting diodes (LEDs) are manufactured by forming active regions on a substrate and by depositing various conductive and semiconductive layers on the substrate. The radiative recombination of electron-hole pairs can be used for the generation of electromagnetic radiation (e.g., light) by the electric current in a p-n junction. In a forward-biased p-n junction fabricated from a direct band gap material, such as GaAs or GaN, the recombination of the electron-hole pairs injected into the depletion region causes the emission of electromagnetic radiation. By using materials with different band gaps, which emit electromagnetic radiation of different wavelengths, it is possible to create different color LEDs. The electromagnetic radiation may be in the visible range or may be in a non-visible range. Further, an LED with electromagnetic radiation emitting in a non-visible range may direct the non-visible light towards a phosphor lens or a like material type. When the non-visible light is absorbed by the phosphor, the phosphor emits a visible light.
It is desirable to use silicon substrates to form LED devices due in part to the low cost of the silicon substrates and the abundance of well-known processing techniques available for processing the silicon substrates. For vertical LED devices, the silicon substrates are used as a conductive interface to provide an electrical connection to the bottom contact layer of the LED structure. The silicon substrates, however, typically exhibit a relatively high light absorption rate, thereby negatively impacting the light efficiency of the LED device.
One method of addressing the problem of silicon substrate absorption is to use a reflective layer, such as a distributed Bragg reflector or a reflective buffer layer, to reflect some of the light away from the substrate to a light-emitting face. The reflective layer, however, may result in a poor crystal quality of the epitaxially grown group III-V layers.
Another method of addressing the problem is to remove the silicon substrate on which the III-V films forming the LED were grown, and then add a new conductive substrate. Problems associated with this method include the sacrifice of the entire silicon substrate, and the time and expense required to remove the silicon substrate.
Accordingly, there is a need for improved methods of fabricating LED devices with increased light efficiency.
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