Investigation of Trapezoidal Well for Improving the Light Efficiency in Algainp-Based LEDs
In this study, we investigate the behaviors of optical and electrical characteristics according to their trapezoidal well profile in the active region through the analysis of optical behaviors and device performances.
To investigate the optical behaviors according to the trapezoidal well shape, the sloped barrier (SB) is inserted between well and flat barrier (FB) and the thickness of SB (dSB) is changed from 2.5 nm to 10 nm. And, the FB thickness is adjusted from 15 to 0 nm to maintain the total barrier thickness 20 nm. The schematic diagram of MQW structures of a trapezoidal-shaped well is depicted in Fig. 1(b).
Fig. 2 shows the device performances having different sloped barrier profiles in the MQW LED structures. As the current is increased to 600 mA, the current-voltage (I-V) curves show different behavior according to the SB thickness. In Fig. 1(a) inset, the forward bias voltage at 350 mA decreases from 2.86 V to 2.62 V with an increase in the thickness of SB from 0 to 10 nm. Fig. 1(b) then shows the light output power (Pout)-current characteristics of LEDs on the dSB and the normalized efficacy of the same LEDs at 350 mA operating current is shown in the figure inset. As the dSB between the well and the barrier is increased from 0 to 5.0 nm, the normalized efficacy improves from 1.0 to 1.16 and the maximum Pout increases from 400 to 500 mA, though at a further increase of the dSB to 10 nm, the normalized efficacy degrades to 0.98.