Lifetime Tests

Room temperature lifetime tests were performed with InGaAs homojunction diodes, un-encapsulated and encapsulated at current pulses of 2A, duration 50 µs and repetition rate of 30 Hz.

Lower figure presents data on the long-term variation of the properties of the uncoated InGaAs homojunction LED s at high temperatures. The upper graph shows the times for which the LEDs under study operated at several ambient temperatures. The samples operated at currents I = 0, 0.5, 1, 2 A for 150 h at room temperature, 450 h at T = 130°C, and 800 h at T =180°C. The LEDs were cooled to room temperature and heated again to T = 130°C eight times and to 180°C three times.

The lower graph shows the output power as a function of the working time. As can be seen, the output power decreased, on average, by 25% after 1400 h of operation. It is noteworthy that the operating current strength has no effect on the degradation of the LEDs. With increasing operating time, the reverse currents at a bias U = 1 V increased from 0.5–1 mA (0 h) to 3–4 mA (1400 h). On “cleaning” the sample surface by etching in CP-4, the reverse current returned to its initial values, and the output power tended to regain its initial value: P(1400 h) = (0.85–0.9)P(0 h).

This confirms that LED encapsulation or by protection with window should increase LED lifetime at elevated temperatures.