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
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
0.51 mA (0 h) to 34 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) =
This confirms that LED encapsulation or by protection
with window should increase LED lifetime at elevated temperatures.