ZnS中Er3+的正向注入电致发光

已报导的三价稀土离子(RE3+)和二价锰离子发光的电致发光器件,都是激发机理为碰撞激发的高场发光器件1,2]。我们研究了znS:RE2+的带边激发光谱,由此提出了实现正向注入下三价稀土离子电致发光的发光器件的设想,这种器件的必要条件是在存在三价稀土离子的区域同时注入电子和空穴。在离子注入的ZnS:Er3+发光二极管上观察到了这种发光,实验证明不是碰撞激发,而是正向注入产生的发光。

FORWARD BIASED INJECTION ELECTROLUMINESCENCE OF Er3+ IN ZnS DIODE

Electroluminescence devices of trivalent rare earth ions(RE3+) and divalent manganese ions reported so far are high field electroluminescence devices with the excitation mechanism of impact excitation1,2]. We have studied the excitation spectra of ZnS:RE3+ around the band gap and recognized the possibility to design devices with forward biased electroluminescence of RE3+. The necessary requirement is the injection of both electrons and holes into the region where RE3+ ions are present. Such electroluminescence has been observed in Er3+ implanted ZnS:Er3+ diode. The observed electroluminescence has been experimentally proven to be forward biased injection electroluminescence, not by impact excitation.The electroluminescence spectra of ZnS:Er3+ diode in the forward bias and the reverse bias are the characteristic spectra of Er3+. The ratios of the intensities of the 18800cm-1 (the transition of 4S3/2 to 4I15/2) emission lines to that of the 18050cm-1 (the transition of 4F9/2 to 4I15/2) emission lines were measured. The ratios aaaaaaaaaaa in the reverse bias are found to increase with the reverse bias(Fig.1(a)),which is direct evidence of impact excitation according to Krupka’s analyses 4]. In contrast, the ratios a in the forward bias are found to be a constant at different forward bias (Fig.1(b)), which shows that the electroluminescence of Er3+ in the forward biased ZnS:Er3+ diode is the forward biased injection electroluminescence, not by impact excitation. Electrons injected from the In contact and holes tunneled from the Au contact give energy to Er3+ ions through certain mechanisms, Er3+ ions are excited and then give luminescence.Since the efficiency of electroluminescence by impact excitation are not high 2,5], the present work gives new clues to raise the efficiency and the brightness of RE3+ electroluminescence.Optimized structures of devices will reduce operating voltage and raise efficiency of the forward biased injection electroluminescence of RE3+.