ZnCdSe/ZnSe非对称双量子阱中的光学特性研究

Optical Characteristics of ZnCdSe/ZnSe Asymmetric Double Quantum Wells

用LP MOCVD技术在GaAs衬底上外延生长了ZnCdSe/ZnSe非对称双量子阱 (ADQW )结构。通过 ps时间分辨光谱、吸收光谱、发射光谱等的研究得到了如下的结果 :在弱激发下 ,观测到ADQW结构中的激子隧穿现象 ;在强激发下 ,在ADQW结构中发现了一个内建电场 ,它将影响激子隧穿 ;首次观测到由激子隧穿引起的在一定温度范围内宽阱的发光强度随温度上升而增加的现象 ;

The ZnCdSe/ZnSe asymmetric double quantum wells(ADQW)samples studied were grown on(100)Si doped GaAs substrates by low pressure(LP)MOCVD. The sample structure consists of a 1μm ZnSe buffer layer followed by ten periodes of Zn 0 72 Cd 0 28 Se/ZnSe ADQW and then a 60nm ZnSe cap layer. Each period of ZnCdSe/ZnSe ADQW includes one narrow ZnCdSe quantum well, one thin ZnSe barrier and one wide ZnCdSe quantum well. Each period of the ADQW was separated by a 40nm ZnSe barrier. Exciton tunneling has been studied in the ZnCdSe/ZnSe ADQW. There are two emission peaks of the time resolved spectra of the ADQW corresponding to n =1 heavy hole recombination from the wide well (WW) and narrow well (NW), respectively. It is obvious that the n =1 heavy hole excitonic emission from the WW dominates the spectra, and the n =1 heavy hole excitonic emission from the NW decreases and disappears gradually with increasing the delay time. Considering the exciton tunneling in the ADQW, this phenomenon can be explained. Under stronger excitation, the tunneling of free electron and free hole are also observed in the ADQW. Due to different tunneling time of free electron and free hole, space charge effect was observed in the ADQW, which leaded to the foundation of the internal electric field. The excitation intensity dependence of the luminescence intensity in the WW and NW as shown in fig.5 can be explained by foundation of the internal electric field. The spontaneous and stimulated emission have been studied in the ZnCdSe/ZnSe ADQW. For spontaneous emission of the ADQW, the exciton recombination both in the NW and WW is influenced by two factors, the exciton tunneling and the thermal dissociation processes. For the NW, the two factors have the same influence on the emission intensity, but for the WW, the influence on the emission intensity of two factors are contrary. The change of the emission intensity in the WW is determined by the stronger one. For stimulated emission of the ADQW, owing to the difference of the energy levels between the WW and the NW, the carriers tunnel from the NW to the WW, which can influence the emission effectively.The carrier tunneling is conductive to lasing from the WW.