Light up-conversion mechanism of type-II dual sub-band superlattices

由两种不同量子能级的单周期超晶格(双子带超晶格)组成的超结构超晶格具有两个光致发光峰。在光致发光峰之间具有中等能量的光的激发下，DSB样品除了下边的峰之外，还发出上能边的峰。我们把这种现象称为光上转换效应。在本研究中，我们研究了第二类ZnSe-ZnTe超晶格的发光机制，测量了不同结构样品的光致发光峰的能量和强度与激发强度的关系。在Ar激光(488 nm，2.54 eV)的激发下，所有样品在He-Ne谱线两侧(633 nm，1.96 eV)都有两个发光峰。在He-Ne激发下，所有样品均出现两个峰。高能侧的发光峰为上转换光，上转换峰的激发强度与发射强度的关系(i<em>~i&lt；ex&gt；^n)的n值均大于1.3。样品中含有较薄的锌硒部件(V.B.)的值为1.7。随着激发强度的增加，所有光致发光峰的能量都发生了蓝移。上转换效应的机制包括两步过程，即V.B.中的隧道效应和第II类能级之间的复合。

The super-structured superlattice which consists of two kinds of single period superlattices with different quantum levels (dual sub-band (DSB) superlattice) shows two PL peaks. Under the excitation with the light with the mid-energy between the PL peaks, the DSB sample emits the peak at the upper energy side additionally to the lower side peak. We call this phenomena as light up-conversion effect. In this investigation, we study the mechanism in the type-II ZnSe-ZnTe superlattice.The dependences of the energy and intensity of PL peaks on the excitation intensity on the samples with various structures were measured. Under the excitation with the light of Ar^+ laser (488 nm, 2.54 eV), all the samples have two PL peaks at both sides of the He-Ne line (633 nm, 1.96 eV). Under the excitation with He-Ne, all the samples indicate both peaks. The PL peak at the higher energy side is the up-converted light.All the n values in the presentation of the excitation intensity dependence of the emission intensity (I_<em>〜I_<ex>^n) of the up-converted peaks were over 1.3. The sample with thin ZnSe parts (barriers in V.B.) has the value of n of 1.7. The energies of all the PL peaks indicate the blue shift with increasing the excitation intensity.The mechanism of the up-conversion effect involves two steps process with the tunneling effect in V.B. and the recombination between the type-II levels.