Efficiency Droop and Effective Active Volume in GaN-Based Light-Emitting Diodes Grown on Sapphire and Silicon Substrates

Onwukaeme Onwukaeme,Ryu Ryu

doi:10.3390/app9194160

Abstract

We compared the efficiency droop of InGaN multiple-quantum-well (MQW) blue light-emitting diode (LED) structures grown on silicon(111) and c-plane sapphire substrates and analyzed the efficiency droop characteristics using the rate equation model with reduced effective active volume. The efficiency droop of the LED sample on silicon was observed to be reduced considerably compared with that of the identical LED sample on sapphire substrates. When the measured external quantum efficiency was fitted with the rate equation model, the effective active volume of the MQW on silicon was found to be ~1.45 times larger than that of the MQW on sapphire. The lower efficiency droop in the LED on silicon could be attributed to its larger effective active volume compared with the LED on sapphire. The simulation results showed that the effective active volume decreased as the internal electric fields increased, as a result of the reduced overlap of the electron and hole distribution inside the quantum well and the inhomogeneous carrier distribution in the MQWs. The difference in the internal electric field of the MQW between the LED on silicon and sapphire could be a major reason for the difference in the effective active volume, and consequently, the efficiency droop.

Highlights

Over the last two decades, there has been remarkable progress in the development of GaN-based light-emitting diodes (LEDs)
InGaN/GaN MQW blue LEDs were fabricated on c-plane sapphire and silicon(111)
Numerical simulations showed that the internal electric field could reduce the effective active volume significantly as a result of the reduced overlap of electron and hole distributions inside a quantum well (QW) and the inhomogeneous carrier distribution in the MQWs

Summary

Introduction

Over the last two decades, there has been remarkable progress in the development of GaN-based light-emitting diodes (LEDs). Owing to its high efficiency and eco-friendliness, LED-based solid-state lighting has been rapidly replacing conventional light bulbs in general lighting and display applications [1,2,3,4,5,6]. The high cost of LED illumination sources is still a hindering factor for increasing their market penetration rate in general lighting applications. One prominent way of lowering the production cost of LEDs is to utilize silicon-based technologies. High-performance GaN-based blue LEDs on silicon have been achieved by overcoming the technological difficulty in their growth caused by the large mismatch in the lattice constant and the thermal expansion coefficients between silicon and GaN [7,8,9,10,11]

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Discussion

Conclusion