Large Junction Red LED

This early device is of unknown origin, but believed to have been made by the 3-5 Research Group of Philips Lighting in Turnhout, Belgium. During the early 1970s, like many traditional lampmakers, Philips established a research and small-scale production group for LEDs. Whereas others quickly gave up after realising the extremely low luminous flux was not really compatible with the illumination business, Philips transferred the business to its semiconductor division and continued LED production until the mid 1980s.

This particular lamp is unusual in that it has a rather large die for its age. Whereas competitive devices typically have a die measuring about 0.25 x 0.25mm, this device is more akin to modern high flux LEDs and measures 1.0 x 1.0mm.

The jet black colouration of the die indicates that it is most likely a gallium arsenide substrate, the upper part of which is suspected to consist of an epitaxially grown n-type gallium arsenide phosphide layer. The surface is doped, possibly with zinc, to form the p-type layer and the semiconductor junction. The large die area necessitates some form of current spreading, and this takes the form of a metallised crosshair with small circle at its centre. This leaves a light emission area of approx 0.75mm diameter. The metallisation is a colourless metal, e.g. platinum or rhodium.

The die is brazed directly to a gold-plated kovar TO-46 transistor header, one lead of which is welded directly to the underside and the other is sealed in glass isolation to form the terminal post. That makes electrical connection to the die metallisation via a single platinum wirebond. A thin layer of transparent epoxy has been applied for protection.
Manufacturer: Philips Lighting
Lamp Voltage: c. 1.80 Volts
Lamp Current:
Lamp Power:
Cap Type: Insulated Au plated wires Ø 0.0175" x 0.1" Pitch
Bulb Type: TO-46 transistor Ø 5.5mm x 2.35 high
Bulb Finish: Clear epoxy
Die Chemistry: GaAsP ?
Luminous Flux:
Luminous Efficacy:
Peak Intensity:
Beam Distribution:
Peak Wavelength: 670 nm
Colour Temperature & CRI: CCT: N/A CRI: N/A
Chromaticity Co-ordinates: CCx: CCy:
Junction Temperature
Rated Lifetime:
Overall Length:
Light Centre Length:
Factory: Turnhout ? Belgium
Date of Manufacture: Circa 1975
Original / Present Value: