مرکز منطقه ای اطلاع رساني علوم و فناوري - Low-frequency response to AlGaAs double heterojunction LED´s

Abstract :

At low frequencies, the optical response of a light emitting diode (LED) to analog intensity modulation is found to decrease, due to the junction-heating effects. This low-frequency response is analyzed using approximated I-P characteristics, and is compared with the experimental results for AlGaAs double heterojunction LED\´s. The transfer function of the low-frequency response can be expressed by $1 - (1- \\phi)/(1+ j\\omega \\tau _{\\sigma })$ , where φ and tauσare the degradation of the fundamental amplitude at lower frequencies normalized to higher frequencies and the thermal time constant with a value of about 10 µs, respectively. It is found that the low-frequency response correlates with the linearity of the I-P characteristics, using the low-frequency degradation factor $\\psi$ expressed by $-10 \\log (1- \\phi)$ in decibels and the linearity coefficient γ defined as ${P(1.5 I{o}) - P(I_{o})}/{P(I_{o}) - P(0.5 I_{o})}$ , where $P(1.5 I_{o})$ denotes the power at 1.5 times of the basic current Io. Also, the current dependence and modulation degree dependence on both degradation factor $\\psi$ and second-harmonic distortion are discussed.