Visible-Light Amorphous Silicon-Nitride Thin Film Light Emitting Diode

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VISIBLE-LI6HT AMORPHOUS SILICON-NITRIDE THIN FILM LIGHT EMITTING DIODE

AND SOMSAK PANYAKEOW WIROTE BOONKOSUM , DUSIT KRUANGAM Semiconductor Device Research Laboratory, Department of Electrical University, Chulalongkorn Faculty of Engineering, Engineering, Bangkok 10330, Thailand. ABSTRACT A visible-light Thin Film Light Emitting Diode (TFLED) having a-SiN:H as a luminescent active layer has been developed. The TFLED has a structure The emission of glass substrate/ITO/p a-SiC:H/i a-SiN:H/n a-SiC:H/Al. color could be changed from red to orange, yellow, green and white-blue by varying the optical energy gap of the i a-Siý:H layer in the TFLED. The brightness was in the order of 0.1-1 cd/m . A series of systematic investigations on the basic properties of a-SiN:H films carrier injection and recombination mechanism in TFLEDs is described. 1.INTRODUCTION

One important aspect for the future of amorphous semiconductors and their alloys is that a lack of long range ordering in the atomic network relaxes the k-selection rules for the optical transitions. This gives rise a high a large optical absorption coefficient and presumably to luminescence efficiency, which can be used in the light emitting devices. The first trial to develop an amorphous visible Light Emitting Diode can be fabricated traced back to the year of 1985,when Kruangam et al. hydrogenated amorphous silicon-carbide (a-SiC:H) p-i-n junctions on a transparent electrode/glass substrate[1-2]. They named the device a "Thin Film Light-Emitting Diode (TFLED)". The amorphous visible TFLED has various advantages over conventional crystalline LEDs. It is available for a low cost and wide-area flat-panel display. It can be operated at much lower voltages as compared with an intrinsic EL device. The emission color of TFLEDs can be varied by adjusting the optical energy gap of the luminescent i-layer. The amorphous TFLED can be formed on various kinds of substrates, e.g., glass, polymer film, ceramic or stainless steel sheets. The highest brightness obtained was high enough to be observed visually, but it is still too low for any practical application as a display. Consequently, for the practical application of TFLEDs an advanced development of new device structures, new materials and new fabrication technologies are required [3]. Hydrogenated amorphous silicon-nitride (a-SiN:H) is also known as a wide band gap material and shows visible-photoluminescence [4]. However, the applications of a-SiN:H seem to be limited to a passivation layer and insulating layer in electronic devices [5]. The aim of this work is to study the possibility of applying a-SiN:H as a new visible luminescent layer in the TFLED. In this paper the basic photoluminescence properties of * On leave from Telephone Organization of Thailand (TOT), Electronic Equipments Repair Center, Thailand. ** Premier Professor Chair since 1993. Mat. Res. Soc. Symp. Proc. Vol. 297. ©1993 Materials Research Society

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a-SiN:H materials are presented. A TFLED using a new structure of p a-SiC:H/i a-SiN:H/n a-SiC:H is