不同厚度CdSe阱层的表面上自组织CdSe量子点的发光性质

利用变温和变激发功率分别研究了不同厚度CdSe阱层的自组织CdSe量子点的发光。稳态变温光谱表明:低温下CdSe量子阱有很强的发光,高温猝灭,而其表面上的量子点发光可持续到室温,原因归结于量子点的三维量子尺寸限制效应;变激发功率光谱表明:量子点激子发光是典型的自由激子发光,且在功率增加时。宽阱层表面上的CdSe量子点有明显的带填充效应。通过比较不同CdSe阱层厚度的样品的发光,发现其表面上量子点的发光差异较大,这可以归结为阱层厚度不同导致应变弛豫的程度不同,直接决定了所形成量子点的大小与空间分布^1]。

Photoluminescence of Self-assembled CdSe Quantum Dots with Different Thickness CdSe Quantum Well Layers

The self-assembled CdSe quantum dots (QDs) were fabricated on GaAs(110) substrate by in mo- lecular-beam epitaxy (MBE) the Stranski-Krastanow (S-K) growth mode.By using temperature depen-dence PL spectra of CdSe QDs with 3ML(monolayer) and 10ML deposition thickness.We found the CdSe QW has strong emission only at low temperature and totally quenched at room temperature.The CdSe QDs keep the emission to room temperature due to the effect of quantum size confinement with three dimensions.As for the 3ML sample,it has six PL peaks from ZnSe barrier;CdSe QDs;1ML;2ML;1LO and 2LO assisted 2ML CdSe QW wetting layers at 20 K,respectively.From 20 to 200 K,the PL intensity of 1ML CdSe QW mono- tonly decrease and the peak energy red shifted heavily with the temperature raising.And we only observe two peaks for Cdso QDs and 2LO assisted 2ML at 300 K.The intensity decrease due to the exciton-phonon cou- pling enhanced with the increasing temperature,while the peak largly red shift was attributeed to the reduced band gap and the exciton-phonon coupling with increasing temperature.As for the 10ML sample,the PL in- tensity of CdSe QDs decrease quickly from 50 to 250 K.The thermal active energy for CdSe QDs is calculat- ed.The energy of 34 meV is less than the differences between CdSe QW emission and CdSe QDs centre peak energy,so we attribute the CdSe QDs PL was quenched from the localized states.The PL intensity suddenly enhance from 250 to 300 K,the process is caused by the localized states released at higher temperature.The ex- citation power dependence of PL intensity spectra which have the linear relation verifies that the CdSe QDs e- mission is the free-exciton radiative recombination.In the mean time,the state filling effect in CdSe QDs is al- so observed by employing excitation power dependence of the PL peaks at 20 K.In comparison the PL spectra of 3ML with 10ML samples at 20 K,it is found that the ratio of CdSe QDs and CdSe QW PL intensities is com- pleteky different,the later(10ML sample) has higher intensity for CdSe QDs.As a result,the different CdSe active layers affect the strain relaxation and form the different size and distribution of CdSe QDs,the 3ML is the critical thickness for CdSe layers grown on the GaAs(110) substrate,while the 10ML is larger than that. So the different strain relaxation results in different CdSe QDs emission between 3ML and 10ML samples.