ZnS中Te等电子中心的时间分辨光谱研究

Time-resolved photoluminescence of Te isoelectronic center in ZnS

用时间分辨光谱研究了很大的Te组分范围内的ZnS1 -xTex(x =0 0 0 5— 0 85 )合金的发光动力学特性 ,结果表明 :不同形态的Te等电子中心具有不同的辐射复合寿命 ,从几个ns到几十个ns的范围内变化 ,当x=0 15左右时 ,寿命达到最大值 (约 4 0ns) .其物理机理源于不同的Te等电子中心具有不同的局域化特性 .当Te组分较小时 ,等电子中心从Te1 逐渐演变到Te2 ,Te3或Te4 时 ,相应发光寿命增加 ,表现出不断增强的激子发光局域化特性 ;而当Te组分较大时 ,Te原子团变得较大 ,其局域势与基体原子势的相互作用增强 ,等电子中心的局域化特性减弱 ,而基体价带扩展态特征变得明显起来 ,相应发光寿命逐渐减小 .还研究了激子束缚能随Te组分的变化以及发光强度随温度的变化关系 ,所得结果进一步支持了时间分辨光谱研究所得到的结论 .

The recombination dynamics of localized exciton in ZnS1-x Te-x ternary alloys has been investigated by time-resolved photoluminescence (PL) in a large Te concentration range from 0.005 to 0.85. It is found that the radiative recombination lifetimes of different Te isoelectronic centers show a significant difference, varying from a few nanoseconds to tens of nanosecond. The lifetime reaches a maximum of ∼ 40 ns in the sample of x = 0.15. The present results could be understood in terms of the exciton localization effect. When the Te concentration is small, the Te isoelectronic centers evolve gradually from a single Te impurity (Te-1) to the Te clusters (Te-n). The exciton localization is enhanced, resulting in the increase of exciton recombination lifetime. When the Te concentration is further increased, the Te clusters (Te-n) become large enough to hybridize the Te localized states and the host valence band states. Therefore I the excitons bound to Te isoelectronic centers become more or less delocalized, resulting in a shorter lifetime. Furthermore, the concentration dependence of the exciton binding energy and the PL intensity variation with temperature have been mearsured. The results further confirm the above conclusion.