PR-CMQB技术提升GaN基发光二极管性能的研究

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"具有减少偏振的Chi多量子势垒的GaN基发光二极管的优势" 在GaN（氮化镓）基发光二极管（LEDs）领域，电子阻挡层（EBL）的设计和优化对于器件性能至关重要。本文探讨了一种新型的电子阻挡层结构——基于极化减少的 chirped 多量子势垒（PR-CMQB），并对其在GaN基LED中的优势进行了深入的数值模拟和实验研究。PR-CMQB的设计旨在解决传统AlGaN EBL和普通CMQB面临的挑战，如电子泄漏和空穴注入效率低下的问题。一、引言 GaN基LED由于其高效率和长寿命，在照明领域的应用前景广阔。然而，由于GaN材料的极化效应，会导致电子在阻挡层的泄漏，以及空穴注入到量子阱的困难，这些问题限制了LED的内部量子效率和光输出功率。PR-CMQB的设计正是为了解决这些问题，以提升器件的整体性能。二、PR-CMQB的优势 1. 内部量子效率提升：数值和实验结果都证实，PR-CMQB LED的内部量子效率高于传统结构。这主要得益于PR-CMQB有效地阻止了电子泄漏到基区，从而增加了在发光区域的载流子复合，提升了发光效率。 2. 光输出功率增加：与单一AlGaN EBL或普通CMQB相比，PR-CMQB LED的光输出功率显著提高。这与内部量子效率的提升密切相关，更多的能量转化为光子，减少了非辐射复合，从而提高了光输出。 3. 空穴注入效率增强：PR-CMQB设计改善了空穴注入到量子阱的能力，这有助于平衡载流子浓度，进一步提升发光效率。 4. 效率下降减少：在高电流密度下，LED通常会出现效率下降现象，称为“效率droop”。然而，采用PR-CMQB的LED显著降低了这一现象，表明其在高工作条件下仍能保持良好的性能。三、PR-CMQB的实现与原理 PR-CMQB通过调整量子势垒的组成和厚度来降低极化效应。这种“chirped”（即变化的）设计使得势垒的带隙宽度沿生长方向连续变化，从而减少电子在阻挡层内的泄漏通道。同时，它也有助于改善空穴传输，增强了整体的载流子注入和复合过程。四、结论 PR-CMQB的引入为GaN基LED提供了一种有效的优化策略，可以显著提高器件的性能，尤其是在高功率应用中。这一创新设计不仅提高了内部量子效率和光输出功率，还降低了效率droop现象，对于推动GaN基LED技术的发展具有重要意义。通过数值模拟和实验验证，PR-CMQB在GaN基LED中的应用展示了显著的优越性，为未来的LED设计提供了新的思路，有望进一步推动照明和显示技术的进步。

IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 61, NO. 8, AUGUST 2014 2849

Advantages of GaN-Based Light-Emitting Diodes

With Polarization-Reduced Chirped

Multiquantum Barrier

Yi An Yin, Naiyin Wang, Guanghan Fan, and Shuti Li

Abstract—The advantages of GaN-based light-emitting

diodes with polarization-reduced chirped multiquantum barrier

(PR-CMQB) as electron blocking layer (EBL) are investigated

numerically and experimentally. Both simulation and experiment

results indicate that the LED with PR-CMQB possesses higher

internal quantum efﬁciency and light output power as compared

with its counterparts with either conventional single AlGaN EBL

or CMQB. These improvements are mainly attributed to the

suppression of electron leakage and the enhancement of hole

injection efﬁciency. Furthermore, the efﬁciency droop is markedly

reduced when the PR-CMQB is employed.

Index Terms— Electron blocking layer (EBL), light-emitting

diodes (LEDs), multiquantum barrier (MQB), polarization.

I. INTRODUCTION

HE GaN-based light-emitting diodes (LEDs) are the

most potential candidates for next-generation illumina-

tion source due to their high lumen efﬁciency, compact

size, and long lifetime [1]. However, the efﬁciency droop is

still a big obstacle for them to be competitive in terms of

high-brightness and high-power applications [2]. Although the

physical mechanisms behind efﬁciency droop is still not fully

understood, it is widely regarded that electron leakage [3] and

poor hole injection efﬁciency [4] are mainly responsible for

this problem. To reduce electron leakage, one common method

is to introduce a larger bandgap AlGaN as electron blocking

layer (EBL) between the multiple quantum well (MQW) active

region and p-type region [5]. However, many recent studies

pointed out that the typical single AlGaN EBL is insufﬁcient to

prevent electron leakage due to the polarization-induced band

bending [3], [6]. Furthermore, as a carrier potential barrier,

the utilization of the single AlGaN EBL severely hinders

holes injection into the active region [7]. Numerous efforts

Manuscript received February 20, 2014; revised April 20, 2014 and

May 31, 2014; accepted June 9, 2014. Date of current version July 21, 2014.

This work was supported in part by the National Natural Science Foundation

of China under Grant 61176043, in part by the Natural Science Foundation

of Guangdong Province under Grant S2011040005150, and in part by the

Ministry of Education of Guangdong Province, Integration of Production and

Research Projects, under Grant 2011B090400401. The review of this paper

was arranged by Editor E. G. Johnson. (Corresponding author: Naiyin Wang).

The authors are with the Laboratory of Nanophotonic Functional

Materials and Devices, Institute of Optoelectronic Materials and Tech-

nology, South China Normal University, Guangzhou 510631, China

(e-mail: yinya@scnu.edu.cn; naiyin.wang@gmail.com; 275171925@qq.com;

936903095@qq.com).

Color versions of one or more of the ﬁgures in this paper are available

online at http://ieeexplore.ieee.org.

Digital Object Identiﬁer 10.1109/TED.2014.2330374

Fig. 1. Schematic diagrams of three LED structures.

related to the design optimization of the EBL have been

made to suppress electron leakage and enhance hole injection

efﬁciency, and therefore to improve the performances of

GaN-based LEDs [8]–[13].

To conﬁne carriers in the active region, multiquantum

barrier (MQB) consisting of a superlattice with thin wells

and barriers, and chirped MQB (CMQB) structure (i.e.,

MQB with modulated-layer thickness) were proposed, respec-

tively [14], [15]. Theoretical calculation indicated that both

structures increase the effective electron potential barrier

height due to the reﬂection and quantum interference of elec-

tron waves therein, but the blocking efﬁciency of the CMQB

structure is more effective [15], which was also experimentally

conﬁrmed in AlGaInP LEDs [16]. Very recently, scientists

have tried to apply the CMQB structure to GaN-based LEDs

to improve devices’ performance [17]–[19]. These researches

exhibited that the LED with a CMQB has higher effective

electron barrier height [17], [18] and hole injection efﬁ-

ciency [19] as compared with LEDs with either uniform MQB

or conventional single AlGaN EBL. However, this paper found

that performance improvement of GaN-based LEDs with a

CMQB in suppressing the spillover of electrons and increasing

the hole injection efﬁciency is still limited due to the serious

band bending of the EBL caused by large polarization effect

generated by the lattice mismatch between GaN and AlGaN

See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.

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