Laser lift-off of very thin AlGaN film from sapphire using selective decomposition of GaN interlayer

Abstract

A very thin 1 μm-thick Al 0.11Ga 0.89N film is successfully separated from a sapphire substrate by thermal decomposition of interfacial region using high power laser, so-called laser lift-off technique. The used layer structure prior to the separation is 1.0 μm Al 0.11Ga 0.89N/0.3 μm GaN on sapphire grown by metal organic chemical vapor deposition (MOCVD), and third harmonic Q-switched Nd:YAG laser ( λ=355 nm) is irradiated from the backside of the sapphire. Absorption of the laser light occurs only at the GaN interlayer and the decomposed thickness is limited up to the interlayer thickness. As a result, a crack-free thin AlGaN film is separated from sapphire with metal Ga underneath through the optimization of the process parameters. In contrast, removal of 2 μm-thick GaN single layer from sapphire is also tested, where peeling-off of the film with cracks is seen. In addition, slight red shift of the peak energy in the cathodoluminescence (CL) spectra of the AlGaN film is observed after the lift-off process, which is due to the relaxation of compressive stress in the film. Thus, separated AlGaN film is free from the disadvantages of using sapphire substrates such as the thermal mismatch, higher series resistance and poor heat dissipation so that it would enable high performance AlGaN-based ultraviolet (UV) light emitters.