222–282 nm AlGaN and InAlGaN‐based deep‐UV LEDs fabricated on high‐quality AlN on sapphire

Abstract

1 Introduction Because of their wide direct transition energy range in UV, which is between 6.2 eV (AlN) and 3.4 eV (GaN), AlGaN and quaternary InAlGaN are attracting considerable attention as candidate materials for the realization of deep ultraviolet (DUV) laser diodes (LDs) or light-emitting diodes (LEDs) [1,2]. DUV LEDs and LDs with emission wavelengths in the range of 230-350 nm are expected for a lot of applications, such as, sterilization, water purification, medicine and biochemistry, light sources for high density optical recording, white light illumination, fluorescence analytical systems and related information sensing fields, air purification equipment, and zero-emission automobiles.Research into AlGaN-based UV LEDs for wavelengths shorter than 360 nm, i.e., wavelengths between 330-355 nm [3][4][5], was initiated by several research groups between 1996-1999. The development of short-wavelength UV LEDs is now becoming extremely competitive. Several groups have reported AlGaN-, InAlGaN-, or AlNbased DUV LEDs, 240-280 nm AlGaN multi-quantumwells (MQWs) LEDs [6-10], quaternary InAlGaN MQW LEDs [1,[11][12][13] and a 210 nm AlN LED [14].We started our research into AlGaN-based deep-UV LEDs in 1997. We reported first efficient DUV (230 nm) photoluminescence (PL) from AlGaN QWs [15], and 333 nm AlGaN-QW UV LED on SiC in 1999 [3]. We have

High-quality AlN layers grown by hot-wall MOCVD at reduced temperatures

“…Different modifications of the so referred migration enhanced epitaxy have been suggested, especially in the context of the fabrication of elaborate, thick, ~ 4 µm, AlN templates on sapphire substrates for the better performance of deep-UV LEDs [10]. The growth of AlN at reduced temperatures has also been enabled by alternating between two-dimensional and three-dimensional growth modes, for which the conditions have been adjusted by changing both, the temperature and V/III ratio, together with a pulsed supply of NH 3 , and achieving thick, 1.5 µm, crack-free, multilayer AlN structure on SiC substrate [11].…”

Status of Growth of Group III-Nitride Heterostructures for Deep Ultraviolet Light-Emitting Diodes

“…[56] In order to obtain AlN and high Al-molar fraction AlGaN with high crystalline quality and flat surface morphology by using moderate growth temperatures, pulsed-flow growth methods, which can effectively promote the surface migration of Al (and Ga and In) adatoms, have been developed instead of the conventional continuous growth. There are at least three types of pulsed-flow growth methods, namely (a) NH3 pulse-flow growth, [17,60] (b) pulsed atomic layer epitaxy (PALE), [61,62] and (c) migration-enhanced metalorganic chemical vapor deposition (MEMOCVD), [63,64] as shown schematically in Figure 5. For the NH3 pulse-flow growth of AlN, pulsed NH3 flow was employed to enhance the lateral migration of Al adatoms, while TMAl flow was kept constant during the NH3 pulsed-flow sequence to ensure Al-rich growth conditions.…”

Overcoming the fundamental light-extraction efficiency limitations of deep ultraviolet light-emitting diodes by utilizing transverse-magnetic-dominant emission

“…One of the most remarkable characteristics of DUV light is that it can strongly damage bacteria and viruses, and for this reason, it has been used in air/water/food purification and sterilization to protect humans from serious health threats. [1][2][3] Other major applications of DUV light include polymer curing, semiconductor photolithography, and high-density optical recording. [3][4][5][6] Currently, man-made DUV light sources are employed for those applications because natural DUV light from the Sun is absorbed by ozone and O 2 molecules in the Earth's stratosphere.…”

“…[1][2][3] Other major applications of DUV light include polymer curing, semiconductor photolithography, and high-density optical recording. [3][4][5][6] Currently, man-made DUV light sources are employed for those applications because natural DUV light from the Sun is absorbed by ozone and O 2 molecules in the Earth's stratosphere. 7 Hg-vapor lamps have been widely used as conventional DUV light sources for over 100 years despite their inefficient energy usage, bulky and heavy structure, and serious environmental burden arising from mercury (Hg) usage and disposal.…”