两种非晶碳化硅薄膜发光二极管

TWO TYPES OF α-SiCx:H THIN FILM LIGHT-EMITTING DIODES

利用硅烷与甲烷的混合气在射频电场下的等离子体反应,淀积不同导电类型的非晶碳化硅薄膜,制成了p-i-n结注入型和均匀材料的碰撞电离型两种大面积发光二极管。本文报导这两种非晶发光器件的结构设计及光谱特性,并对器件的发光机现进行了讨论。

Visible light-emitting diodes either with a structure of glass/ITO/p a-SiC:H/i a-SiC:H/n a-SiC:H/Al or with a structure of glass/ITO/ a-SiC:H/Al have been developed by the glow discharge deposition in SiH4 + CH4 mixture. The p-i-n LEDs exhibit characteristics of switching diode with turn-on voltage of about 16V, while the another type of LED exhibits characteristics of avalanche breakdoswn in a uniform medium with threshold field of about 1.5×108V/cm. The two types of aSiC:H thin film LEDs named injection LED and impact ionization LED, respectively, emit visible white light when their own critical conditions are established. Both of them have a broad lightemission band centred around 2.0eV and extend over the whole visible range. The peak energy of injection LED's spectrum does not change as the injection current increases, but the peak energy of the impact ionization LED's spectrum changes from 1.87 eV to 2.04 eV when the avalanche current increases from 0.15 mA to 6 mA. The optical gap of a-SiC:H thin films,including either n- or p-doped layers, is maintained at 2.2 eV by adjustments of the deposition parameters and measured according to Tauc plot. The irradiation recombination mechanizm concerned with these LEDs is suggested to be a transition between the extended states in conduction-band and the localized states in valence-band tail.The variation of peak energy of the impact ionization LED's spectrum is attibuted to the energy distribution of excess electrons in conduction-band, which is dependent on the excitation voltage.