The Effect of Imbalanced Carrier Transport on the Efficiency Droop in GaInN-Based Blue and Green Light-Emitting Diodes

Abstract

Abstract:The effect of strongly-imbalanced carrier concentration and mobility on efficiency droop is studied by comparing the onset voltage of high injection, the onset current density of the droop, and the magnitude of the droop, as well as their temperature dependence, of GaInN-based blue and green light-emitting diodes (LEDs). An n-to-p asymmetry factor is defined as σ n /σ p , and was found to be 17.1 for blue LEDs and 50.1 for green LEDs. Green LEDs, when compared to blue LEDs, were shown to enter the high-injection regime at a lower voltage, which is attributed to their less favorable p-type transport characteristics. Green LEDs, with lower hole concentration and mobility, have a lower onset current density of the efficiency droop and a higher magnitude of the efficiency droop when compared to blue LEDs. The experimental results are in quantitative agreement with the imbalanced carrier transport causing the efficiency droop, thus providing guidance for alleviating the phenomenon of efficiency droop.

Improving radiative recombination efficiency of green light-emitting diodes

“…Green LEDs generally have a lower onset current density of efficiency droop [51,61,62] and a higher magnitude of droop, compared to blue LEDs [51,61]. Nevertheless, current density is not the only criterion of measuring efficiency droop.…”

Realization of Highly Efficient InGaN Green LEDs with Sandwich-like Multiple Quantum Well Structure: Role of Enhanced Interwell Carrier Transport

“…11,12 In addition, the straininduced internal polarization field will tilt the green LED band diagrams of QWs more seriously than those of blue ones, leading to a so-called "efficiency droop" in InGaN-based green LEDs, which has been attributed to the inefficient hole transport and increased electron overflow out of the active region. 13,14 These two problems have seriously hampered the development of SSL, especially for high-power LEDs, whose operating current is usually greater than 350 mA and even up to 1 A, having dimensions of approximately 1 × 1 mm 2 . 15 Many efforts have been made to solve these two problems, such as designing novel MQW structures 14−16 or optimizing growth parameters.…”

“…Additionally, in order to incorporate In sufficiently, it is usually accomplished by sacrificing the growth temperature of InGaN quantum wells (QWs), resulting in a significant deterioration of the material quality in the QWs due to crystal defects. , On the other hand, the higher In composition in well layers induces a larger piezoelectric polarization electric field, resulting in a quantum confinement Stark effect (QCSE). The QCSE restricts the internal quantum efficiency (IQE) by reducing the overlap integral between the electron and hole wave functions, resulting in a lower recombination efficiency. , In addition, the strain-induced internal polarization field will tilt the green LED band diagrams of QWs more seriously than those of blue ones, leading to a so-called “efficiency droop” in InGaN-based green LEDs, which has been attributed to the inefficient hole transport and increased electron overflow out of the active region. , These two problems have seriously hampered the development of SSL, especially for high-power LEDs, whose operating current is usually greater than 350 mA and even up to 1 A, having dimensions of approximately 1 × 1 mm 2 …”

Fundamental Limitations of Wide-Bandgap Semiconductors for Light-Emitting Diodes

“…For example, Auger recombination would be expected to be more pronounced in low-bandgap semiconductors and at higher temperatures, contrary to the experimental results. 45 The results presented above along with the analysis of the underlying causes allow for a coherent understanding of the efficiency droop in a wider context, including its dependence on bandgap energy and temperature.…”