The development of a universal substrate technology for the growth of light emitting diodes

This paper reviews the use of alternative substrate technologies, ZnO and Si, for III-Nitride materials and devices grown by Metalorganic Chemical Vapor Deposition (MOCVD). ZnO offers many advantages for the III-Nitrides due to its closely matched lattice constant and similar thermal expansion coefficients. Si is a readily available material and can be chemically removed to provide a thin III-Nitride device structure. However, when using ZnO, H₂ etching of the ZnO substrate at high temperatures and Zn diffusion out of the ZnO substrate have limited its use. Moreover, a tensile stress can occur between III-Nitrides and Si, and a potential reaction between Ga and Si can cause many issues during MOCVD growth. In this work we have used a transition layer on these substrates to promote the crystallinity of the III-Nitride materials and resulting device structures. We show that thin layers (5-200 nm) of Atomic Layer Deposited (ALD) AI₂O₃ can be used for this function. Wurtzite III-Nitrides were obtained for thin AI₂O₃/ZnO and AI₂O₃/Si with a mirror-like surface, no etch pits, and no peeling. In addition, light emitting diodes on ALD AI₂O₃/Si have shown a similar device performance to those grown on sapphire. This transition layer technology could provide a universal substrate technology for III-Nitride LEDs crystal growth.