Free-standing GaN-based LEDs with ALD-Al_2O_3/Si substrate removedby wet etching

摘要

High quality InGaN-based LEDs have been grown on Si (111) substrates using an A1_2O_3 transition layer. Freestanding, fabricated LED devices were achieved by removing the Si substrate using selective area wet etching. Conventional device design was used for LED fabrication, in which p-type and n-type contacts are located at the same side of the epilayers. These LED devices were bonded to a dual in-line package (DIP), and epoxy was used to protect the front side of the epilayers thin films as well as the bonding wires. The Si substrate was removed by wet etching while the chip was mounted in the DIP which prevented the thin film from cracking or warping.Electroluminescence (EL) characteristics of the LED devices grown on ALD/Si were measured before and after substrate removal. No significant change in peak emission wavelength was observed, nor any change in EL intensity versus drive current. No degradation of electrical and optical properties was observed. This indicates that the devices were not damaged by the wet etching process. However, the luminescence intensity of devices both before and after wet etching did not increase beyond a drive current of ~60 mA due to inefficient heat dissipation. The process developed and the challenges involved in the larger area substrate removal process will be discussed which could be substantially beneficial to the future substrate transfer and packaging in the industrial fabrication of LED on silicon substrate.