CdSe/ZnSe复合结构非对称量子阱的发光特性

利用MOCVD技术在GaAs衬底上外延生长了非对称量子阱结构CdSe/ZnSe材料,通过对其稳态变温光谱及变激发功率光谱,研究了其发光特性。稳态光谱表明:在82～141K时,观测到的两个发光峰来源于不同阱层厚度的量子阱激子发光,用对比实验验证了高能侧发光的来源。宽阱发光强度先增加后减小,将其归结为激子隧穿与激子热离化相互竞争的结果。通过Arrhenius拟合,对宽阱激子热激活能进行了计算。82K时变激发功率PL光谱表明:由于激子隧穿的存在,使得窄阱发光峰位不随激发功率变化而变化,宽阱发光峰位随激发功率增加发生了蓝移,并对激子隧穿进行了实验验证。

Photoluminescence of CdSe/ZnSe Asymmetric Quantum Wells

The CdSe/ZnSe asymmetric quantum wells sample were grown on GaAs substrates by MOCVD.The samples consist of a 112 nm ZnSe buffer layer followed by two 22ML and a 10MLs CdSe quantum wells and then a 51 nm ZnSe cap layer.The ZnSe barriers between the quantum wells are 34 nm and 3.9 nm,respectively.A single quantum wells was also prepared as a comparison with the asymmetric quantum wells.It contains three 10ML CdSe quantum wells separated by a 34 nm ZnSe barrier and it was fabricated at the same condition with the asymmetric quantum wells.Spontaneous emission has been studied in the CdSe/ZnSe asymmetric quantum wells.There are two emission peaks of the photoluminescence spectra of the sample corresponding to n=1 heavy hole exciton recombination from the wide well(WW) and narrow well(NW) in the temperature range of 82 to 141 K,respectively.The emission peak of the NW can not be seen after 141 K and is identified by the spontaneous emission spectrum of the single quantum wells at 82 K.The exciton recombination both in the NW and WW is influenced by two factors:the exciton tunneling and the thermal dissociation processes.For the WW,the influences on the emission intensity of two factors are contrary.The change of the emission intensity in the WW is determined by the stronger one:the exciton tunneling plays the more important role in the temperature ranging from 82 K to 141 K and the thermal dissociation processes play the more important role for the rest of the temperature.For stimulated emission of the CdSe/ZnSe asymmetric quantum wells,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.Space charges caused by different tunneling rate between electrons and holes lead to the formation of the internal electric field which affects carriers tunneling.As the result of the internal electric field effect,the changing of the electrons density excited with excitation intensity is super-linear.The carrier which decides the changing of the peak energy in the wide well is exciton which comes from two sources,one is excited by photon in the wide well,and the other one is that tunneling from the narrow well.