Luminescence Properties of Photonic Crystal InGaN/GaN Light Emitting Layers on Silicon-on-Insulator

Abstract

The photonic crystal InGaN/GaN light emitting diodes ͑LEDs͒ on thin silicon-on-insulator ͑SOI͒ substrates are demonstrated. Surface nanopatterning has been carried out on such LED layers and the processing conditions are varied to improve the outcoupling of visible emission. A substantial increase in the photoluminescence intensity is observed from LEDs on a thin SOI overlayer as compared to a similar structure grown on a thicker SOI. In addition, enhancement of the cathodoluminescence and electroluminescence intensity from such photonic crystal LEDs shows their potential in solid-state lighting.According to the present solid-state lighting research, the luminescence efficiency of InGaN/GaN light emitting diodes ͑LEDs͒ can reach 80%. 1 Major LED manufacturing companies now focus on the development of high power and high brightness devices with suitable packaging for general illumination market. 1-3 An alternate low cost solution for street lighting and general illumination for GaN LEDs could be the use of large-area Si-based substrates. 4,5 One of the major concerns for the LEDs on Si substrate is the absorption of blue-green light emitted from InGaN/GaN multiquantum well ͑MQW͒ active layers. In this context, substrate removal is a necessary step to realize high brightness LEDs. An alternate solution is to grow LED structures on a large-area, thin reflective Si-on-insulator ͑SOI͒ substrates. 6,7 Recently, majority of research groups have been exploring two-dimensional ͑2D͒ photonic crystal ͑PhC͒ structures to improve the light-extraction efficiency ͑LEE͒ for high brightness LEDs. [8][9][10][11][12][13][14][15] In this study, we have carried out surface nanopatterning to enhance light emission from GaN-based LEDs on large-area silicon-based substrates. The LEDs with photonic nanostructures on thin SOI show substantial photoluminescence ͑PL͒, cathodoluminescence ͑CL͒, and electroluminescence ͑EL͒ intensity enhancement.The InGaN/GaN LEDs were grown by metallorganic chemical vapor deposition on SOI͑111͒ substrates with SOI overlayer thickness in the range of 45 to 200 nm with a buried oxide ͑BOX͒ thickness ranging from 150 to 375 nm. The full LED structure consisted of a high temperature buffer layer, an Al-rich intermediate layer, a 2.75 m n-type thick Si-doped GaN, five periods of InGaN/ GaN MQWs, and a 120 nm Mg-doped p-type GaN layer. For the light extraction study, we used two sets of LED samples, where layers were grown on thin SOI ͑45-50 nm overlayer with 150 nm BOX: green emission ϳ525 nm͒ and thick SOI ͑200 nm overlayer with 375 nm BOX: emission ϳ485 to 490 nm͒ substrates. The fabrication of 2D PhC structures on the LED surfaces was carried out by electron-beam lithography and dry etching of GaN using a SiO 2 nanomask. 7 The microscopic PL and EL spectra were recorded from the PhC structures using a Jobin Yvon LABRAM setup equipped with 325 nm excitation from a He-Cd laser. The low temperature CL measurements were carried out in a JEOL scanning electron microscope ͑SEM͒ equipped with a helium cryostat. To de...

Enhanced Light Extraction of GaN Based Blue Light-Emitting Diode with SiO2/ITO Photonic Crystal Structure

“…This result is attributed to a PBG where photons with frequencies within the PBG are not allowed to propagate but coupled to escape into the air in a vertical direction. [8][9][10][11][12][13][14][15][16] Figure 3a shows the scanning electron microscope (SEM) images of the SiO 2 pillars formed on a 200 nm-thick ITO layer on the p-GaN in blue LEDs, where the SiO 2 pillars have a radius, period, and height of 75 ± 5 nm, 256 ± 3 nm, 225 ± 5 nm, respectively. These results agree well with the simulation results shown in Fig.…”

“…In addition, photonic crystal (PC) structures, materials with a spatially periodic refractive index, have also been investigated in an attempt to improve η extraction . [8][9][10][11][12][13][14][15][16] To this end, LEDs comprised of PC structures have been designed to efficiently couple light from guided modes into air. 8,9 Until now, 2-dimensional (2D) PC structures used to enhance η extraction in IIInitride-based LEDs have generally been fabricated directly in the p-GaN layer.…”

“…8,9 Until now, 2-dimensional (2D) PC structures used to enhance η extraction in IIInitride-based LEDs have generally been fabricated directly in the p-GaN layer. [10][11][12][13][14][15][16] The formation of a PC structure in the p-GaN layer, however, requires the use of plasma dry etching, which subsequently results in plasma damage to the p-GaN layer and sometimes even to the multiple quantum well (MQW) layer. 12 The plasma dry etching process was reported to produce surface defects such as vacancies, impurities, and residuals, resulting in the degradation of electrical properties of p-GaN.…”

Enhanced Light Emission of InGaN Light-Emitting-Diodes by Nanosphere Lithography Generated Photonic Crystals with Different Geometries

“…Moreover, lattice constant of PhCs on the wavelength-scale is preferable to the light extraction of GaN based LEDs. Until now, 2dimensional (2D) PhC structures used to enhance LEE in GaN-based LEDs have generally been fabricated directly in the p-GaN layer [9][10][11] since LEDs with patterned p-GaN layer exhibit a more effective light extraction. 12,13 Traditionally, nano-patterning used to fabricate 2D PhC structures relies heavily on techniques such as high-precision directz E-mail: zhy168@semi.ac.cn write electron-beam lithography (eBL), 14 but the drawbacks of lowthroughput and high equipment cost impede this from applying to mass fabrication.…”