[19a-E202-1~10] 15.4 III-V-group nitride crystals

▲ [19a-E202-6] EQE enhancement of AlGaN Based Lower Bound (295±nm) UVB-LED by using high reflective Ni/Mg electrode for medical applications.

〇Muhammad Ajmal Khan¹, Takuma Matsumoto^1,2, Noritoshi Maeda¹, Masafumi Jo¹, Norihiko Kamata², Hideki Hirayama^1,2 (1.Hirosawa Wako, Saitama, 351-0198, Japan, 2.Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan)

Keywords:LP-MOVPE, AlGaN, UVB LED

UV-LED has a number of sensing applications, i.e., for many gases (e.g., SO₂, NO_x, NH₃) and biomolecules, which exhibit absorption bands in UV-B and UV-C LEDs spectral regions, including tryptophan, NADH, tyrosine, DNA, and RNA respectively. Recently it was found that the phytochemicals in the fruits and vegetables can be enriched by using UVB light with NB, 310nm, even with mild output power about 20mW. Fruits and plants enriched with phytochemicals can greatly reduce the risk of cancer as well as cardiovascular diseases. It has been reported that an onset rate of the atopic dermatitis is more than 10% in Europe, America and 2-3 % in the entire Japan, which can be cured by NB, UVB LEDs. UVB(280nm-320nm) LED is quite important for immunotherapy, skin care, cancer treatment, wound healing, and prevention of the plant blight. Very recently Boston University, of USA discovered that LB(293nm), UVB LED light source is 2.4 times more efficient than the sunlight for producing Vitamin D3 in the human body. Therefore we attempted to further improve the performance of smart, cheap and environmentally safe AlGaN based UVB LED on AlN template with EL emission around 293nm for the production of vitamin D3 in the human body. In this work, 4-μm thick AlN template on sapphire substrate having XRC around 300 arcsec both for (002) and (101) diffraction respectively were used for the growth of LB-UVB LED structure. Subsequently a 1.34μm Si-doped n-Al_0.5-0.6Ga_0.4-0.5N as n-type contact layer on the epitaxial AlN layer, and then an over layer of active region, multiple quantum well (MQWs) consisting of a three-fold Al_0.35Ga_0.65-0.67N(1.5-2.5nm)/Al_0.44Ga_0.55-0.60N(6.5nm) were deposited. As we know that it is very challenging to achieve a reasonable hole concentration having shallow donor energy level in an AlGaN alloy with high Al mole contents, therefore two fold thin p-Al_0.65GaN layer (10nm), as an electron blocking layers (MQBs) were inserted between MQWs and p-AlGaB. The p-side of the device was completed by lightly Mg-doped p-Al_0.6Ga_0.4N layer and heavily doped p-Al_0.1Ga_0.9N as a p-contact layer respectively. As a result, single peak PL/ EL emission of 294±3 nm were obtained and EQE was limited to 2.7% due to the transmitted light loss through Ni electrode. When we replaced the Ni electrode with highly reflective (Ni/Mg) electrode then EQE were enhanced from 2.7% to 3.5% at the current 20mA with output power around 12.7mW. This LB(294nm)-UVB LED might be 2.4 times more efficient than the sunlight for producing Vitamin D3 in the human body.