||Although GE is well known as being inventor of the first visible light emitting diodes, this work was preceded by developments with infrared emitters. The first infrared LED, known as the SNX-100, employed a pure GaAs crystal to emit a 900nm output and was created earlier in 1962 by Gary Pittman and Rober Biard at Texas Instruments. In the same year Nick Holonyak at GE achieved the first visible LED by working with gallium arsenide-phosphide materials, which reduced the wavelength sufficiently to achieve red light.
The mid 1960s then witnessed a great diversification of products as GE's LED range grew. Soon joining the original red emitters were the SSL-1 and SSL-6 devices based on Silicon carbide, emitting a tiny amount of yellow coloured light. GE next entered the infrared market with its SSL-4, a pure GaAs device similar to that of Texas Instruments.
Pure GaAs has the advantage of an extremely rapid rise and decay time on switching, around 50ns, which permits high frequency signalling at speeds of up to around 100MHz. However the infrared output is very low. GE improved on this by adding silicon atoms, which shifts the wavelength to around 940nm and increases output power tremendously. That material was first employed in this SSL-5A LED. However it does increase the rise and decay time to several hundred nanoseconds, such that switching frequencies of 1MHz are the limit and it is not suitable for all applications.
The construction of this LED is similar to others of its era : a gold plated kovar transisor header to which the chip is bonded. Owing to the absorption of infrared wavelengths by many traditional plastic encapsulants, a glass lens is used.