UV‐LED Using p‐Type GaN/AlN Supperlattice Cladding Layer

Abstract

PACS : 78.55.Cr; 78.66.Fd; 78.67.De; 85.60.Jb GaN/AlN supperlattice was used as the p-type cladding layer of UV-LED. I-V characteristics indicates that UV-LED having GaN/AlN supperlattice has much lower series resistance than the conventional UV-LED in which ternary alloy AlGaN was used as the cladding layer.Introduction High efficiency light emitting diodes (LEDs) in blue and green region based on group III nitride semiconductors have been developed by achieving several breakthroughs such as improvement of the crystalline quality of GaN using a low-temperature-deposited (LT-) buffer layer technique [1] and realization of conductivity control of nitrides [2][3][4]. In these devices, GaInN-based quantum wells are usually used as an active layer.Fabrication of UV devices will surely give a big impact on the applications such as super high-density optical storage, chemical sensing, flame detection, excitation source for phosphors or fine lithography. In order to establish such UV-devices, thick AlGaN films with high-AlN molar fraction and high-crystalline quality, high-efficiency AlGaN alloys active layers and low-resistance and wide-bandgap p-cladding layers are essential.We succeeded to grow high quality and thick AlGaN free of cracks using an LT-AlN interlayer technique [5]. High-sensitivity flame sensor was developed using this technique [6,7]. Transmission electron microscopic study showed that the pure screw-type and mixed-type dislocations in the AlGaN films were reduced, while high-density pure edge-type dislocation was still contained as high as mid 10 9 cm --2 in these films [8]. Therefore, the fabrication of highly luminescent AlGaN was difficult.In order to reduce all types of threading dislocations in GaN, novel growth technique called "epitaxial lateral overgrowth" has been performed and led to the success of growing partially very low dislocation density GaN [9]. Unfortunately, due to a strong adhesion of AlN on the mask surface, polycrystalline AlGaN is formed on the mask, which prohibits epitaxial lateral overgrowth of AlN containing alloys [10]. Moreover, this technique has the problem of crack generation. We succeeded to reduce all types of threading dislocations by combining low temperature interlayer and lateral growth technique. Details of the growth procedure have been reported elsewhere [11][12][13]. PL

Monolayer‐Thick GaN/AlN Multilayer Heterostructures for Deep‐Ultraviolet Optoelectronics

“…[54,55] In this regard, the first demonstration, in 2002, of binary GaN:Mg/AlN SLs instead of ternary AlGaN layers in the p-type cladding layer of UV LED should be mentioned. [56] 2.5. Summary of the Open Issues in Al-Rich AlGaN Layers Thus, the low values of the quantum efficiency and output power of AlGaN-based UV emitters are largely due to the high concentrations of the extended and point defects arising during the heteroepitaxial growth and doping of AlGaN layers on commercially attractive sapphire substrates.…”

“…[ 54,55 ] In this regard, the first demonstration, in 2002, of binary GaN:Mg/AlN SLs instead of ternary AlGaN layers in the p‐type cladding layer of UV LED should be mentioned. [ 56 ]…”

The Effect of Interface Diffusion on Raman Spectra of Wurtzite Short-Period GaN/AlN Superlattices

“…Quantum wells (QWs) based on layers of GaN compounds in a wider gap AlN matrix and GaN/AlN SLs are considered for use in the architectures of many optoelectronic devices in the ultraviolet (UV) range as active regions [ 2 ] or reflective Bragg mirrors [ 3 ]. Many problems in the production of high-performance UV lasers and light-emitting diodes can be solved, inter alia , through the use of extended GaN/AlN SLs (also called digital solid solutions, or digital alloys), which provide doping of the emitter layers with a high average Al content (>40 mol%) [ 2 , 4 ]. A significant contribution to the development of nitride microwave electronics can be made by resonant microwave diodes based on GaN/AlN QWs [ 5 ], and microwave transistors based on GaN/AlN SLs [ 6 ].…”

Short‐period AlN/GaN p‐type superlattices: hole transport use in p‐n junctions

“…This is attributed to an increase in the polarization charges induced at the interfaces, causing larger band bending in the wells and consequently higher ionization of the acceptor atoms. If AlN barriers are used in place of the AlGaN, more conductive p-type layers can be obtained [16]. These conductive sheets of carriers will be spatially separated, meaning vertical transport can be limited.…”