Effect of p-GaN layer on the properties of InGaN/GaN green light-emitting diodes
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Guoqiang Lia) State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou 510640, China; and Department of Electronic Materials, School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, China (Received 4 August 2014; accepted 2 January 2015)
InGaN/GaN green light-emitting diodes (LEDs) have been prepared by metal-organic chemical vapor deposition with various growth temperatures for p-GaN layer. The structural and optoelectronic properties of as-grown multiple quantum wells (MQWs) and LEDs are studied in detail. It reveals that with the growth of p-GaN layer, the crystalline qualities of the as-grown n-GaN layer are improved significantly, while the optoelectronic properties of MQWs are decreased dramatically. Furthermore, the mechanisms for the effect of p-GaN growth temperature on the properties of InGaN/GaN green LEDs are proposed. It is demonstrated that the p-GaN layer grown at a suitable temperature of 950 °C shows the highest optoelectronic properties due to the fact that this suitable temperature for p-layer growth is good for the Mg doping and would not cause the fluctuation of indium in the MQWs, and eventually benefits to the effective recombination of carriers. This work provides an optimized p-GaN layer growth temperature for realizing highly efficient InGaN/GaN green LED devices.
I. INTRODUCTION
The III-nitrides including the semiconductors AlN, GaN, and InN form a continuous AlGaInN alloy system with direct band gaps, ranging from about 0.7 eV (InN) to 6.2 eV (AlN) with 3.4 eV for GaN. Band gaps from 0.7 to 6.2 eV could be obtained by suitable alloy combinations in the AlGaInN system to tailor the band gap energy of the active region spanning the entire UV and visible ranges.1–4 Therefore, the III-nitride semiconductors have attracted considerable attention as promising materials for the application of light-emitting diodes (LEDs), especially, in general lighting and liquid crystal display backlighting, and most of outdoor commercial displays.5,6 As the rapid improvement of nitride semiconductor epitaxial growth technology, the internal quantum efficiency (IQE) for red and blue LEDs has achieved above 50 and 60%, respectively.7,8 However, as for the green LEDs, it is just about 30%. So far, tremendous works have been pursued to address the efficiency issue in InGaN-based LEDs.9,10 The existence of electrostatic fields in InGaN quantum well (QW) results in charge
Contributing Editor: Joan Redwing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2015.5 J. Mater. Res., Vol. 30, No. 4, Feb 28, 2015
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separation issue.11,12 For the InGaN/GaN green LEDs, high indium composition is required for the growth of InGaN/GaN multiple quantum wells (MQWs), which results in the high piezoelectric field in MQWs.13–17 This leads to the formation of quantum confined Stark effects (QCSEs) and subsequently causes the separation of electrons an
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