摘要
本文首次报道了VPE ZnS_xSe_(1-x)外延膜在77K时起因于激子和激子(Ex—Ex)散射的自发辐射和受激辐射,研究了Ex—Ex散射发光的位置和强度与激发密度的关系,分析了受激辐射的光子能量比自发辐射稍低的原因.
The spontaneous and stimulated emission in Ⅱ - Ⅵ compounds such as CdS, CpSe and ZnSe have been studied [1-5] . In this paper, we report the first observation of spontaneous and stimulated emission at 77 K in VPE ZnSxSe1-x epilayers, which were grown on (100)GaAs substrate[6] .The diagram of experimental setup is shown in Fig.1.Usually, there is only E band in the photoluminescence (PL) spectra in VPE ZnSxSe1-x epilayers excited with 337.1 nm line of a N2 laser at 77K, as shown in Fig.2. E band should be attributed to the free ex-citon recombination scattered by electrons [ 7 ] .Fig.3 shows the near band edge emission spectra of VPE ZnS0.1Se0.9 epliayer at 77K. E band (438.5 nm) is dominant in the spectrum at the low excitation density and P band becomes higher and higher with increasing the excitation density. The arrow in Fig.3 shows the energy position of free exciton band (Ex), determined according to references [8-11], At low excitation density, the energy separation between Ex and P band is about 23meV, which nearly equals to the free exciton binding energy of ZnS0.1Se0.9,22meV(the values of exciton binding energy of ZnSe and ZnS are about 20meV and 39meV[12] , respectively,so the exciton binding energy of ZnSxSe1-x can be determined by assuming a linear varation of binding energy with composition x[13]). The above fact indicates that the P band is produced mostly by the inelastic. collision process of two excitons (Ex-Ex) [141 , In Fig. 3 it is observed that P band shifts towards the low energy part of the spectrum when the exciting light intensity increases. This result can be explained with Levy's[15] model, which gives the shift of P band, △S∝J173, where J is the excitation density, Fig. 4, shows the relation of AS and J.From Fig.4,it is observed that the experimental data is in good agreement with the theoretical curve. The intensity of P band (Ip) grows with a superlinear relation of Ip∝J1.8 as shown in Fig.5. Saito[1] obtained the relation of Ip∝J1.9 in ZnSe crystal at 1.8K. Above results indicate that P band is due to Ex-Ex emission.The stimulated emission spectra in VPE ZnSxSe1-x(x = 0.1,0.2) epi-layers at different pumping density at 77K are shown in Fig.6 (solid). Fig.7 shows the intensity dependence of L line vs. pumping density. It exhibits that above the pumping density threshold (arrowed)the depen-ence becomes exponential, clearly indicating the stimulated character. L line should be due to Ex-Ex emission. In Fig.6, it is observed that the energy position of L line is a little bit lower than that of P band. This result is in explanation of that the fall-off of laser gain with wavelength is less rapid than that of absorption tail[1,2].
出处
《发光学报》
EI
CAS
CSCD
北大核心
1991年第2期98-104,共7页
Chinese Journal of Luminescence
基金
国家自然科学基金
中国科学院重大综合基础基金
