Mobile phones, personal digital assistants (“PDAs”), digital cameras, MP3 players, and other portable electronic devices utilize light-emitting diodes (“LEDs”), organic light-emitting diodes (“OLEDs”), polymer light-emitting diodes (“PLEDs”), and other solid-state transducer (“SST”) devices for, e.g., backlighting. SST devices are also used for signage, indoor lighting, outdoor lighting, and other types of general illumination. FIG. 1A is a cross-sectional view of a conventional SST device 10a with lateral contacts. As shown in FIG. 1A, the SST device 10a includes a substrate 20 carrying an LED structure 11 having an active region 14, e.g., containing gallium nitride/indium gallium nitride (GaN/InGaN) multiple quantum wells (“MQWs”), positioned between N-type GaN 15, and P-type GaN 16. The SST device 10a also includes a first contact 17 on a forward-facing surface of the P-type GaN 16 and a second contact 19 spaced laterally apart from the first contact 17 on a forward-facing surface of the N-type GaN 15. The first contact 17 typically includes a transparent and conductive material (e.g., indium tin oxide (“ITO”)) to allow light to escape from the LED structure 11. FIG. 1B is a cross-sectional view of another conventional SST device 10b in which the first and second contacts 17 and 19 are at opposite sides of the LED structure 11, e.g., in a vertical rather than lateral configuration. In the SST device 10b, the first contact 17 typically includes a reflective and conductive material (e.g., aluminum) to direct light toward the N-type GaN 15.
Several elements of the SST devices 10a and 10b shown in FIGS. 1A and 1B (e.g., the LED structure 11) can be grown epitaxially or otherwise formed on engineered substrates. Engineered substrates, such as silicon-on-insulator (“SOP”) substrates, typically include a ceramic or glass substrate carrying a thin layer of silicon or other material that facilitates epitaxial growth. FIG. 2, for example, is a cross-sectional view of a conventional engineered substrate 22 during a manufacturing stage in which a formation structure 24 (e.g., a single crystal silicon) is transferred from a donor wafer 26 to a handle wafer 28. As shown in FIG. 2, the handle wafer 28 includes a substrate material 30 (e.g., ceramic or glass) and a defect mitigation material 32 (e.g., an oxide or nitride material) disposed on a forward-facing surface 34 of the substrate material 30. The defect mitigation material 32 reduces defects 36 (e.g., pits and voids) in the forward-facing surface 34 of the substrate material 30 such that the handle wafer 28 has a substantially smooth front surface 38 on which the formation structure 24 can be attached.
The donor wafer 26 can be doped with an exfoliation agent (e.g., hydrogen, boron, etc.) using an ion implantation process such that a portion of the donor wafer 26 (e.g., the formation structure 24) can later be separated from the donor wafer 26 via exfoliation. The donor wafer 26 is typically made from a material (e.g., silicon with an Si(1,1,1) crystal orientation) that has relatively low shear stress. Therefore, any defects 36 in the surface 38 of the handle wafer 28 not cured by the defect mitigation material 32 form weak points in the bond between the donor wafer 26 and the handle wafer 28 that may result in shear tear-out across the defects 36. As shown in FIG. 2, for example, a portion 40 of the formation structure 24 proximate the defect 36 in the handle wafer 28 tears away from the handle wafer 28 and remains with the donor wafer 26 is removed. Such voids or other defects in the formation structure 24 can affect epitaxial growth and translate defects to the SST structure that is subsequently formed thereon.
USPTO Backgrounds
USPTO Backgrounds