Compatible with Si-CMOS nano-column LEDs for more accurate photon integration

Researchers at the University of California, Berkeley, showcased three-five (III-V) family of nanopillar LED designs that are compatible with Si-CMOS optical lithography , while also controlling the precise growth of these nano-LEDs. It is a key element for efficient integration of photons in CMOS circuits for fast on-chip optical interconnects.

In the "ACS Photonics" journal, the researchers published "InP nanopillar LEDs on silicon with bright electroluminescence on silicon crystals with teleluminescent wavelengths" (Ultracompact Position-Controlled InP Nanopillar LEDs on Silicon with Bright Electroluminescence at Telecommunication) Wavelengths) pointed out that the growth rate of the growth position is as high as 90%, and a uniform array of indium phosphide (InP) nanopillars can be realized on the silicon crystal, and grown under CMOS compatible conditions: low temperature and no catalyst.

A low-magnification SEM image of a position-controllable InP nanopillar array grown at 460 °C. The scales in all images correspond to 10 μm and 1 μm, 4 μm and 40 μm growth cycles (pitch).

The researchers began with a clean silicon wafer (111), depositing 140 nm of dioxide into a nanometer-scale pore diameter of about 320 nm at 350 ° C, and positioning the nanocolumn nucleation sites at a pitch of 1 μm - 40 μm. After the researchers chemically roughened the surface of the silicon crystal, the InP nanostructures were grown in the MOCVD chamber at a temperature of 450 ° C to 460 ° C. The researchers found that the cone angle of the nanocolumn is significantly affected by the growth temperature, producing nanoneedles at 450 °C and almost vertical columnar structures at 460 °C.

Based on these nanopillars, the researchers incorporated five indium gallium arsenide (InGaAs) quantum wells into the active region of the pn diode through a concentric core-shell growth to form an electrically driven n-InP/InGaAs MQW/p-InP/p-InGaAs nano-LED.

Nano column MQW LED assembly schematic

Due to the core-shell growth pattern, the nanopillars grow from their nucleation sites and extend beyond the oxide openings to a final diameter of about 1 μm. Thus, when the n-doped core of the nano-pillar is in direct contact with the n-Si substrate, the p-doped outer shell grows on the oxide shield, eliminating the shunt path from the p-doped outer shell and the n-Si substrate. 20/200 nm Ti/Au is evaporated by a tilted electron beam to a highly p-doped InGaAs contact layer, completing the assembly to form an electrical contact, wherein a small portion of the nano-pillar is exposed and no metal is emitted as LED light. window.

Characterization of nano-columnar LEDs was performed at 1510 nm and a quantum efficiency of about 30%. Although the nanopillar LED has a small footprint, it can output 4μW, which researchers claim is the highest light output record that can be achieved from nanopillar/nanostructured LEDs. Under this build, the available light output is reduced to 200nW due to a collection efficiency of only 5%.

Another interesting aspect of the study is that the component can generate optical gain with electrical bias and exhibit a strong photoresistance during reverse injection, which helps to achieve photonic integration on the chip.

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