Electroluminescence Characteristics of Inorganic (p-GaN/MgO)-Organic (Alq 3 ) Hybrid p-n Junction Light Emitting Diodes
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Electroluminescence Characteristics of Inorganic (p-GaN/MgO)-Organic (Alq3) Hybrid p-n Junction Light Emitting Diodes Akihiko Kikuchi and Tomoyuki Tsuji Department of Engineering and Applied Sciences, Sophia University, 7-1, Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan
ABSTRACT Inorganic/organic hybrid light-emitting diodes (LEDs) (IO-HyLEDs) composed of p-type GaN/n-type Tris-(8-hydoroxyquinoline) aluminum (Alq3) were fabricated with and without thin MgO electron-blocking layer (EBL) at the inorganic/organic interface. These LEDs showed clear and stable current rectifying diode characteristics and electroluminescence (EL) peaked at UV region at room temperature. For the sample with MgO-EBL, obvious enhancement of green emission from Alq3 layer was observed. This result suggests that due to effective suppression of electron transport from Alq3 to p-GaN by MgO-EBL, radiative recombination of electrons and holes in Alq3 layer was enhanced. It was indicated that the band engineering technique can be applied to control the emission property of inorganic/organic hybrid LED. INTRODUCTION Recent progress of visible light emitting diode (LED) technology based on inorganic semiconductor and organic semiconductor have expanded application fields of LED to display and solid state lightning. From the point of view of energy conservation and reduction of environmental burdens, further improvement of light emission efficiency and reduction of fabrication cost of LEDs will be required. The inorganic and organic semiconductors have complementary advantage and disadvantage each other. For example, inorganic semiconductors (e. g. GaN based system) have superior electrical conductivity, environmental resistance and potential of advanced band-engineering technology. However, the best performance can be obtained in limited wavelength region such as blue region [1], and it requires expensive and complicated fabrication technology. On the other hand, organic semiconductor has potentiality of relatively high internal quantum efficiency close to 100% using phosphoresce [2] which may cover wavelength range of entire visible region due to a large variety of organic materials and of low fabrication cost. However, in generally, the electrical conductivity and environmental resistance of organic materials are poor. The hybrid combination of inorganic and organic semiconductor [3, 4] is an attractive approach to develop higher performance and lower cost optoelectronic devices. It is expected that adequate hybrid combination of inorganic and organic semiconductors overcome each disadvantage by a complementary effect. Some pioneering researches on inorganic/organic hybrid LED structures are reported so far, it is still difficult to realize efficient light emission from organic active layer by carrier injection from inorganic cladding layer [5-9]. Recently, multiple luminescences from both organic and inorganic layers of hybrid LED were reported [10, 11]. Precise understanding and clear concept for effective carrier
injection to organic active lay
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