The 6N138 consists of a GaAℓAs infrared emitting diode coupled with a split-Darlington output configuration. A high speed GaAℓAs Ired manufactured with an unique LPE junction, has the virtue of fast rise and fall time at low drive current.

The 6N138 is ideal for TTL applications since the 300 % minimum current transfer ratio with an LED current of 1.6 mA enables operation with one unit load-in and one unit load-out with a 2.2 kΩ pull-up resistor