CdSe/ZnSe自组装量子点中非线性系数随着温度的规律性变化(英文)

An Inerratic Variation of Nonlinear Coefficient with Temperature in CdSe/ZnSe Self-assembled Quantum Dots

研究了在CdSe/ZnSe自组装量子点中CdSe量子点的发光随着激发光强度变化的特性。发现当激发强度(I)变化3个数量级的时候,量子点发光的峰位、峰形都没有发生明显的变化。通过公式L∝Ik(其中I是激发光强度,L是量子点发光强度,k是非线性系数)得到非线性系数k值。实验结果表明:在温度由21 K升高到300 K的过程中,k值随温度变化可以分为3个区域:当温度低于120 K时,k值接近于1;然后,随着温度升高,k值慢慢变小;最后,随温度进一步升高,k值由200 K时的0.946迅速减少到0.870。结合发光随温度变化的实验结果,确认在120 K以下发光主要来源于束缚激子复合。在温度由200 K升高到300 K的过程中,非线性系数的单调减小主要归因于随着温度的升高,发光部分来自于由自由电子或空穴到束缚态能级(FB)的复合。进一步通过分析量子点发光的积分强度随着温度的变化的实验结果,发现发光强度随温度升高而减弱的主要原因是材料中的缺陷或者位错等提供非辐射渠道。

We have investigated the excitation-intensity-dependent optical properties of CdSe/ZnSe self-assembled quantum dots（QDs） at different temperature.When excitation intensity（I） is varied by three orders of magnitude,the photoluminescence（PL） morphology and peak positions appear to be independent on excitation intensity.The nonlinear coefficient k obtained by a relation of L∝Ik in the temperature ranges of 21～300 K shows regularity which is described in three temperature regions：k is close to 1,when the temperature is below 120 K,it slightly decreases with increasing temperature in ranges of 120200 K and it rapidly decreases from 0.946 to 0.870 with the temperature in the ranges of 200300 K.Taking the temperature dependence of PL into account,we have confirmed that the bound excitonic recombination is a dominant recombination mechanism below 120 K.The nonlinear coefficient k monotonously decreases in the temperature ranges of 120300 K,which is attributed to increasing transition from free-to-bound（FB） exciton with increasing temperature.Furthermore,the temperature dependence of integrated PL intensity reveals that defects and dislocations in the material provide nonradiative channels to quench the luminescence.