Abstract: The present application discloses a composite substrate with a protective layer for preventing metal from diffusing, comprising: a thermally and electrically conductive layer (2) having a melting point of greater than 1000° C., and a GaN mono-crystalline layer (1) located on the thermally and electrically conductive layer (2). At least the side wall of the composite substrate is cladded with a protective layer (3) for preventing metal from diffusing. The composite substrate not only takes account of the homoepitaxy required for GaN epitaxy and improves the quality of the crystals, but also can be used directly to prepare LEDs with vertical structures and significantly reduce costs. The disclosed composite substrate effectively avoids the pollution of experimental instruments by the diffusion and volatilization of a metal material during the growth of MOCVD at high temperature.

Abstract: A method for preparing a composite substrate for GaN growth includes: growing a GaN monocrystal epitaxial layer on a sapphire substrate, bonding the GaN epitaxial layer onto a temporary substrate, lifting off the sapphire substrate, bonding the GaN epitaxial layer on the temporary substrate with a thermally and electrically conducting substrate, shedding the temporary substrate, and obtaining the composite substrate in which the GaN layer having a surface of gallium polarity is bonded to the conducting substrate. If the GaN layer on the sapphire substrate is directly bonded to the conducting substrate, after the sapphire substrate is lifted off, a composite substrate in which a GaN epitaxial layer having a surface of nitrogen polarity is bonded to the conducting substrate. The disclosed composite substrates have homoepitaxy and improved crystal quality; they can be used for forming LED and other devices at greatly reduces costs.

Abstract: A solid-state laser lift-off apparatus comprises: a solid-state laser (1), a light beam shaping lens (3), motors of oscillating mirrors (5,7), oscillating mirrors (4,6), a field lens (9), a movable platform (10), an industrial control computer and control software (8). The light beam shaping lens (3) is behind the solid-state laser (1), shaping the laser beam from the solid-state laser (1) into required shape. The motors of oscillating mirrors (5,7) are in front of the field lens (9), controlling the movement of the oscillating mirrors (4,6) according to the instruction of the control software (8) to implement different light beam scanning paths. A lift-off method for applying the solid-state laser lift-off apparatus uses a small laser spot to perform scanning, and enables damage-free separation of GaN from a sapphire substrate.

Abstract: A method for nondestructive laser lift-off of GaN from sapphire substrates is disclosed. A solid-state laser is used as the laser source. A small laser-spot having a perimeter length of 3 to 1000 micrometers and a distance of two farthest corners or a longest diameter of no more than 400 micrometers is used for laser scanning point-by-point and line-by-line. The energy at the center of the laser-spot is the strongest and is gradually reduced toward the periphery. A nondestructive laser lift-off with a small laser-spot is achieved. The scanning mode of the laser lift-off is improved. Device lift-off can be achieved without the need of aiming. As a result, the laser lift-off process is simplified, and the efficiency is improved while the rejection rate is reduced. The obstacles of the industrialization of the laser lift-off process are removed.