Integration of InGaN-based Optoelectronics with Dissimilar Substrates by Wafer Bonding and Laser Lift-off
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Integration of InGaN-based Optoelectronics with Dissimilar Substrates by Wafer Bonding and Laser Lift-off
William S. Wong, Michael Kneissl, David W. Treat, Mark Teepe, Naoko Miyashita, and Noble M. Johnson XEROX Palo Alto Research Center, 3333 Coyote Hill Road, Palo Alto, CA 94304, USA ABSTRACT InGaN-based optoelectronics have been integrated with dissimilar substrate materials using a novel thin-film laser lift-off process. By employing the LLO process with wafer-bonding techniques, InGaN-based light emitting diodes (LEDs) have been integrated with Si substrates, forming vertically structured LEDs. The LLO process has also been employed to integrate InGaN-based laser diodes (LDs) with Cu and diamond substrates. Separation of InGaN-based thin-film devices from their typical sapphire growth substrates is accomplished using a pulsed excimer laser in the ultraviolet regime incident through the transparent substrate. Characterization of the LEDs and LDs before and after the sapphire substrate removal revealed no measurable degradation in device performance. INTRODUCTION Often the enhancement of integrated microsystems requires the integration of thin-film materials with disparate properties. Many examples may be found currently in the III-nitride optoelectronic field. For example, today’s most advanced high-performance (In,Ga,Al)N laser diodes (LDs) possessing lifetimes greater than 10000 hours have been realized on sapphire substrates1 although a major impediment to the development of III-nitride LDs still remains the efficient dissipation of heat generated from the device active area. The high thermal resistance of the sapphire substrate and the high diode current densities combine to degrade the device performance and lifetimes due in part to excessive heating during operation. Although substrates such as silicon or copper would be more ideal, integration by direct deposition and fabrication of III-nitride-based laser devices on these materials are either impracticable or result in poor-quality devices. Similarly, the integration of InGaN-based blue light-emitting diodes (LEDs) on low-cost materials such as Si, glass or polymers suffers from substantial sacrifices to the microstructural quality and device performance. Integration of these disparate materials systems though would allow cost-effective applications in color displays, high-resolution laser printers, high-density optical storage devices, high-power electronics, bioanalytical microsystems and room lighting based on the III-nitrides materials system. A viable alternative integration method to preclude the direct deposition of the III-nitrides onto disparate substrate materials is through wafer bonding and thin-film lift-off processes. For example, a fully functional InGaN-based blue LD originally fabricated and optimized on its growth sapphire substrate could be separated and transferred onto another host material such as copper or Si in order to further enhance the functionality of the blue LD. Such an approach allows the integration of materials selected
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