| Semiconductor light-emitting diodes (LEDs) is one of very important light-emitting devices due to their wide application in many fields, such as display, lighting, integrate circuit, light-storage, light-communication, etc. It is so important for LEDs that the studies related to their electrical and optical characterization have been a very interesting subject in the past and today. In this paper, the forward electrical characteristics of LEDs is studied systemcally, and our work and achievement can be summarized as follows:1.We set up experimental measurement devices including the low frequency measurement device and the voltage modulated electroluminescence (VMEL) device; and we also made development and improvement for TH2819 Precision LCR Meter in connecting with a computer, which increased our measurement efficiency greatly.2 By using the forward ac small signal method, we tested the electrical characteristics of LEDs of different kinds and functions in frequency between 20Hz and 100kHz and analyzed the experimental results in different voltage regions systemcally.3.By using the low frequency measurement device, we tested the capacitance characteristics of LEDs in frequency between 1Hz and 20Hz. The experimental results verified that the capacitance of LEDs is negative all the time if LEDs emit light brightly in this frequency .4.By using the voltage modulated electroluminescence (VMEL) device, we tested the relative luminous intensity and the phase angle of light of LEDs and explained the experimental results qualitatively.5 . In the frequency region that we tested, the phenomenon of negative capacitance of LEDs exist in most semiconductor LEDs; the negative capacitance phenomena becomes stronger at lower frequencies and larger forward bias; and the results of the voltage modulated electroluminescence experiment verified that besides the radiative recombination of the injected... |
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