A maker known as Dr. Semiconductor has produced home fabricated LED chips from a gallium nitride epiwafer, bonded them to a printed circuit board using electroplated indium bumps, and coaxed them into emitting white light, pushing home semiconductor fabrication well beyond the demonstration stage.
Most amateur chip-making projects stop at proving a process works. Dr. Semiconductor is working toward something more practical: a reliable method of bonding chips directly to PCBs. The immediate challenge with that goal is alignment. When a silicon wafer is opaque, it is nearly impossible to line up its underside pads with the copper on a board beneath it. Transparent LED chips sidestep the problem, making them a logical trial run for the bonding technique.
From Epiwafer to Glowing LED Chip
The starting material is a gallium nitride (GaN) epiwafer, a layered sandwich of n-doped GaN, an indium gallium nitride quantum well layer, and p-doped GaN, all grown on a sapphire substrate. When current flows through that structure, electrons from the n-type layer and holes from the p-type layer recombine inside the quantum well, and the energy released comes out as blue light.
Getting electrical contacts onto both layers requires cutting through the p-type and quantum well regions to reach the n-type layer underneath. In a commercial fab this would be done with reactive ion etching in chlorine. Dr. Semiconductor replaced that with a 355-nanometre ultraviolet laser, which breaks GaN down into gallium metal and nitrogen gas. The cut is then cleaned with a potassium hydroxide etch, and the process parameters matter here: a solution of 0.8 wt% KOH in deionised water, held at 80 °C for one hour, dissolves the metallic gallium residue and attacks the laser-damaged, defective material preferentially, while leaving pristine c-plane GaN largely untouched.
It is worth dwelling on the laser step. This is a Class 4 UV laser with an invisible beam capable of causing instant eye damage. Dr. Semiconductor notes that 355 nm-rated goggles and a fully enclosed working area are non-negotiable requirements, not optional precautions.
With the layers accessible, contacts were formed by depositing a photoresist mask, sputtering nickel, silver, and titanium onto the surface, and then using a developer solution to dissolve the mask and lift off the unwanted metal. Apply current between the two contacts, and the LED glows bright blue.
Bonding the Home Fabricated LED Chips to a Board
Mounting a home fabricated LED chip onto a PCB is where the process becomes genuinely novel. Dr. Semiconductor first diced the wafer into individual chips using the same ultraviolet laser. He then electroplated indium bumps onto a printed circuit board, positioned each chip above its bumps, applied rosin flux, and reflowed the indium. The result is a mechanically and electrically sound joint, with the PCB powering the LED directly.
Blue is the natural output of a GaN LED, which is why most commercial LED assemblies add a phosphor conversion layer on top. To produce white light, Dr. Semiconductor mixed cerium-doped yttrium aluminium garnet (YAG) phosphor powder into clear silicone and spread it over the chip. The phosphor absorbs some of the blue photons and re-emits yellow light; the human eye reads the combined blue and yellow output as white.
Context and What Comes Next
This appears to be the first inorganic LED fabricated and documented in a home setting at this level of completeness, taking the device from raw epiwafer through dicing, bonding, and phosphor conversion. Previous home semiconductor projects have tended to stop well short of a packaged, board-mounted component.
The indium bump bonding technique Dr. Semiconductor has refined here is the same mechanism he intends to use for opaque silicon chips, where the transparency trick is unavailable and alignment must be achieved by other means. The LED work is, in his framing, a proof of process rather than a finished product line.
The tip came via Hackaday contributor SpuriousIndices. Full process details, including the KOH etch parameters and laser safety requirements, are documented on Dr. Semiconductor’s own site.
