Study of trap levels in Alq3 layers by photodipolar absorption
Study of trap levels in Alq3 layers by photodipolar absorption
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DOI：
10.1051/epjap:2005072
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发表时间：
2005-11
影响因子：
1
通讯作者：
A. Moliton;W. Rammal;B. Lucas
中科院分区：
文献类型：
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作者：
A. Moliton;W. Rammal;B. Lucas
本文讨论了8-三羟基喹啉铝（Alq_3）在传统电子结构ITO/Alq_3/Al中的电子电导中涉及的陷阱部分，给出了一般模型，讨论了有机材料中迁移率的表达式，给出了光偶极吸收的结果，这是一种热-光-介电效应，以及通过阻抗谱测量。最后一种方法允许定义等效电路，该等效电路可以被设计为单个电容器Cp和并联电阻器Rp网络，串联电阻50位于阳极侧;作为直流偏置电压的函数的对数-对数曲线Rp给出了线性规律，该线性规律可以在第一时间作为捕获电荷限制电流（TCL）的结果而被看到;该TCL定律可以通过引入场相关迁移率来改进。事实上，光偶极吸收导致更有说服力的论点，因为这种方法作为一个探针，突出的陷阱：特别是，我们表明，光泵的电子陷阱水平给出了一个明确的增加所产生的介电吸收的偶极子与陷阱电荷的重新取向;陷阱深度位于约Et = 0.19eV，这是与理论计算或热释光测量良好一致的值。
In this paper we develop arguments about the part of traps involved in the electronic conductivity of the 8-tris-hydroxyquinoline aluminium (Alq3) studied in the conventional electronic structure ITO/Alq3/Al. After the presentation of general models and some topical discussions about the expression of the mobility in organic materials, we present results obtained by photodipolar absorption, which is a thermo-photo-dielectric effect, and by impedance spectroscopy measurements. This last method permits to define the equivalent circuit that can be designed as a single capacitor C p and parallel resistor R p network with a series resistance 50 located on the anode side; the log – log plot R p as a function of the dc bias voltage gives a linear law that can be seen in a first time as a consequence of a Trapped Charge Limited current (TCL); this TCL law could be improved with the introduction of a field dependent mobility. Indeed, the photodipolar absorption leads to more convincing arguments because this method acts as a probe to highlight the traps: in particular, we show that the optical pumping of electrons on trap levels gives a clear increase in the dielectric absorption generated by the reorientation of dipoles associated with trapped charges; the trap depth is located around E t = 0.19 eV, which is a value in good agreement with theoretical calculations or thermoluminescence measurements.