Response Speed and Optical Investigation of InGaN/GaN Multiple Quantum Well Light Emitting Diodes (LED)

Abstract

Transmission experiments for a local area network (LAN) using blue light emitting diodes (LEDs) with InGaN/GaN multiple quantum well (MQW) and plastic optical fibers (POFs) have been demonstrated. Audio analog signals have been transmitted upto 1800 kHz, which corresponds to optical 1.5 dB bandwidth of LED response. Response speed of these diodes has been investigated by changing operating conditions; DC bias, pulse amplitude and pulse shape. The LED rise time is reduced from 0.26 μs to 0.19 μs by changing the electrical pulse amplitude from 0.5 V to 1.2 V, respectively, whereas the fall time (0.20 μs) unchanges. On the other hand, the fall time is reduced from 0.20 μs to 0.14 μs by adding negative pulses after the applied positive pulses. It is made clear that direct-modulation speed of these diodes is limited by the time constant associated with device-capacitance. Electro-luminescence and photocurrent spectra of LEDs are also investigated and blue shifts have been observed for both peaks in the spectra.