Scientists in Taiwan have developed a highly efficient heterogeneous structure of silicon LED

According to Taiwan media reports, silicon is the most commonly used materials in the microelectronics industry, but because of its non direct band (indirect bandgap), light-emitting efficiency is very low. Recently, a team led by Professor Chen Minzhang and Professor Yang Zheren of National Taiwan University's Department of materials science and engineering, using Zinc Oxide n / silica silicon nano crystalline silica /p type silicon substrate (n-ZnO/SiO2-Si nanocrystal-SiO2/p-Si) heterostructure, successfully made high efficiency silicon light emitting diode, opened a new opportunity for the application of non direct band semiconductor at the photo.

The team first developed silicon nanocrystals on P type silicon substrates by low pressure chemical vapor deposition (LPCVD) method, and then embedded them in the silica layer by thermal oxidation (thermal oxidation). Then we use the ZnO (Atomic Layer Deposition, ALD) to produce high quality n type thin film, as a transparent conductive layer, an electron injection layer and an anti reflection layer which can improve the light extraction rate. ALD nano thin film deposition technology, with atomic level precision thickness and composition control of forming a thin film, also has high uniformity, low defect density, large batch production, and the deposition temperature is low.

Electron micrographs clearly show that the silicon nanocrystals with a diameter of about 24 nm are embedded in the silica layer with a thickness of about 9.2 nm. The electrons and holes are respectively made of N type ZnO film and P type silicon substrate, and the tunneling (Tunneling) enters the silicon nanocrystal through the silicon dioxide layer. The electron hole pair is limited in a small crystallite, silica and repair effect on ceramic surface defects, so the electron hole pairs generated luminescence (radiative recombination) with the probability increase, coupled with the transparent ZnO thin film anti reflection effect, thus greatly luminous efficiency of light emitting diode or silicon.

The components of the room temperature photoluminescence spectrum peak at the wavelength of 1140 nm, very close to the silicon bandgap energy, corresponding to the non direct carrier phonon assisted combination (phonon-assisted indirect carrier recombination) physical mechanism. The researchers also measured the luminous power injected into different DC currents. This component at room temperature, the external quantum efficiency is 4.3 * 10-4, is 100 times the bulk silicon substrate, the internal quantum efficiency that is about 10-3, broke through the non direct band semiconductor limited.

It is worth mentioning that the process and structure of this component is fully compatible with the existing VLSI technology, which can be directly integrated in the current integrated circuits. The results of this study are expected to be applied in the integrated circuit interconnection (optical) and integrated optical path (photonic integrated circuits) required for high efficiency silicon light-emitting diodes.