Abstract

SiO₂Al₂O₃ double dielectric stack layer was deposited on the surface of the GaN-based light-emitting diode (LED). The double dielectric stack layer enhances both the electrical characteristics and the optical output power of the LED because the first Al₂O₃ layer plays a role of effectively passivating the p-GaN surface and the second lower index SiO₂ layer increases the critical angle of the light emitted from the LED surface. In addition, the effect of the Fresnel reflection is also responsible for the enhancement in output power of the double dielectric passivated LED. The leakage current of the LED passivated with Al₂O₃ layer was -3.46 × 10^-11 A at -5 V, at least two and three orders lower in magnitude compared to that passivated with SiO₂ layer (-7.14 × 10^-9 A) and that of non-passivated LED (-1.9 × 10^-8 A), respectively, which indicates that the Al₂O₃ layer is very effective in passivating the exposed GaN surface after dry etch and hence reduces nonradiative recombination as well as reabsorption of the emitted light near the etched surface.

Keywords

GaN; Light-Emitting Diode (LED); Al₂O₃; PEALD; Passivation; Double Dielectric Stack Layer

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1. Introduction

The III-nitrides are suitable materials for photoelectronic applications covering most of the electromagnetic spectrum due to their wide range of direct bandgap energy. Light emitting diodes (LEDs) are promising semiconductor devices for solid state lighting. Due to a remarkable development in LED fabrication technologies, the LEDs are now being commercialized in various applications such as traffic signals, full-color displays, back lighting in liquid-crystal displays, and so on [1]. However, further improvement in output power with long life time is still required for the GaN-based LED to be more efficiently used in such a field. The increase of the external quantum efficiency (η_EQE), which can be determined from the product of injection efficiency (η_inj) × radiative efficiency (η_rad) × extraction efficiency (η_ext), is the most important factor in achieving a high efficiency LED. η_inj and η_rad can be increased by improving the crystal quality and optimizing the epitaxial layer structure which maximizes the radiative recombination in active region. Surface passivation with appropriate dielectric layers is also necessary to avoid non-radiative recombination for high η_rad [2]. Special techniques such as control of surface roughness [3-5], preparation of patterned sapphire substrate (PSS) [6,7], application of flip-chip bonding [8-10], adaption of laser lift-off process [11], and formation of photonic crystal structure [12] are frequently used to improve η_ext, which can be increased by increasing the critical angle for the emitted light through an appropriate modification of the surface of the LED [13,14]. Anti-reflection (AR) coating of dielectric layers is frequently used to reduce the Fresnel reflection at the semiconductor-air interface in communication LEDs.

In this work, we report, in more detail, the development of passivation technique for the GaN-based LEDs by using double dielectric stack layer design is not optimized for the maximum anti-reflectivity.

2. Device Fabrication

Figure 1(a) shows the schematic LED configuration investigated in this work. The layer structure was grown on the patterned sapphire substrate (PSS) by metal-organic chemical vapor deposition (MOCVD). The blue LED structure contains low temperature grown GaN buffer layer, un-doped GaN layer, Si doped n-GaN layer, InGaN/GaN multi-quantum well active layer and Mg doped p-GaN cladding layer. The composition and thickness of InGaN/GaN multi-quantum well active layer was opti-

Conflicts of Interest

The authors declare no conflicts of interest.

References