薄膜电致发光瞬态过程的物理模型及定量计算

A PHYSICAL MODEL OF TFEL TRANSIENT PROCESS AND ITS QUANTITATIVE EVALUATION

本文利用桥式平衡电路及Sawyer-Towre电路系统地测量了薄膜电致发光(TFEL)器件的损耗电流波形,发光亮度波形及电荷电压回线.在实验基础上建立了TFEL电子传输过程的物理模型和等效电路,由克希霍夫定律可建立激活层的瞬态电压及电流的微分方程,由此导出损耗电流波形,发光亮度波形及Q-V回线的数学表达式.利用计算机模拟将计算结果与实验进行比较,利用四个调节参数即得到与实验相当好的拟合。

The dissipative current waveform, brightness waveform and charge voltage characteristics of the TFEL device with MISIM structure have been measured by using a bridge circuit and Sawyer-Tower circuit, in which a sinusoidal voltage is used. It is observed that the positive half cycle waveform of the dissipative current and the negative one are asymmetry. The brightness waveform has the same propertyOn the basis of experiments, a physical quantitative model for electron transport process has been proposed. At first, a equivalent circuit of the TFEL device is set up. By the use of Kirchoff's law the transient voltage Vs(t) and the nonlinear current IRs(t) across the active semiconductor layer can be described as follows. Here Cs and Cf are the capacitance of the actives emiconductor layer and the insulating layers respectively; V(t) is driving voltage.The current IRs is considered to be composed of three parts: bulk resistance, tunneling from the interface states and all the mentioned electrons to be multiplied. So the current IR, should be expressed byin which r is the bulk resistance:. P(t), the tunneling probability of electron from the interface state;Nd(t), the density of the interface state and M(t), the impact ionization multiplication factors. Vs(t) and IR, can be solved from the equations ( 1 ) and ( 2 ). The dissipative current, brightness waveform and the charge-voltage characteristics can be calculated from VS(t) and IRS(t). With the aid of computer simulation, the calculated solutions can be compared with results measured directly. The pare-meters appeared in the formula can be determined by the experiments. Only four parameters are treated as adjustable parameters. Computer simulation shows that with reasonable values of these parameters, best fit with expeiimental curves can be reached assuming a distribution of interface . state near Al electrode side. It in turn shows that this model is neatly satisfactory. The values of the parameters determined by computer simulation provide a basis for further study of the behavior of such kind of device.