LEDs are optoelectronic devices that make pn junctions from compound materials. It has the electrical properties of a pn junction device: IV, CV, and optical: spectral response, luminescence, directional, time, and thermal properties.
LED electrical characteristics
A. IV characteristics
Characterize the main parameters of the LED chip pn junction preparation performance. The IV characteristics of LEDs have non-linear, rectifying properties: unidirectional conductivity, that is, the application of a positive bias exhibits low contact resistance, and vice versa.
(1) Positive dead zone: (Fig. oa or oa' segment) point a for V0 is the turn-on voltage, when V
(2) Forward working area: current IF is exponential with applied voltage
IF = IS (e qVF/KT –1) ------------------------- IS is the reverse saturation current.
When V>0, the forward working area IF of V>VF rises with the VF index IF = IS e qVF/KT
(3) Reverse dead zone: pn junction plus reverse bias when V<0
When V = - VR, when the reverse leakage current IR (V = -5V), GaP is 0V and GaN is 10uA.
(4) Reverse breakdown area V
B. CV characteristics
The LED chip has 9×9mil (250×250um), 10×10mil, 11×11mil (280×280um), 12×12mil (300×300um), so the pn junction area is different, which makes the junction capacitance (zero offset). Pressure) C≈n+pf or so.
The CV characteristics are quadratic (see Figure 2). The 1 MHz electromagnetic signal was measured with a CV characteristic tester.
C. Maximum allowable power consumption PF m
When the current flowing through the LED is IF and the tube voltage drop is UF, the power consumption is P=UF×IF.
When the LED is working, the applied bias voltage and bias current must cause the carrier to recombine and emit a part of the heat, which causes the junction temperature to rise. If the junction temperature is Tj and the external ambient temperature is Ta, then when Tj>Ta, the internal heat is transferred to the outside through the stem, and the heat dissipation (power) can be expressed as P = KT(Tj – Ta).
D. Response time
The response time characterizes how quickly a particular display tracks changes in external information. There are several display LCDs (liquid crystal displays) of about 10-3~10-5S, and CRT, PDP, and LEDs all reach 10-6~10-7S (us level).