【摘要】 随着激发密度的增加,ZnSe外延单晶膜的室温蓝带Es′(～4650?)表现出红移和展宽,其行为与77K时得到的相一致。在200—300K温度范围内,测得Es′谱带的热激活能为19meV,它与ZnSe晶体自由激子的束缚能20meV十分接近。上述结果从实验上进一步证明了ZnSe外延单晶膜室温蓝带Es′起源于受导带中自由电子散射的自由激子的衰减。更多还原

【Abstract】 Blue electroluminescence of ZnSe MIS diodes had been obtained in the near band edge emission region[1,2] and the stimulated emission had also been observed in this region[3,4]. Many work in the origin of the blue emission of ZnSe at room temperature (RT) had been reported. The blue emission of ZnSe at RT was contributed by free exciton emission[5], the overlapping between free exciton emission and band-to-band transition[6], the emission due to the excitons which bounded to neutral donors[7], the band-to-band radiative recombinations[8] , the bound-to-free transitions[9], and the exciton-carrier interaction[10,1].In our earlier work, attention was focused on the identification of the free exciton emission[11] and the determination of the origin of the blue emission band[1] in ZnSe crystals. In this paper the recombination process of the blue emission at RT from VPE ZnSe epilayers was studied. It was found that the origin of the blue emission at RT could be contributed by the exciton-carrier interactions.The ZnSe epilayers Were grown on GaAs substrates by VPE method. The growth details was reported in our earlier papers[2,12]. Fig.1 showed the photoluminescence (PL) spectra of ZnSe epilayers at RTand 77K. The spectrum at 77K showed a strong near band edge emission, labeled Es band, and no selfactivated deep center emission was observed. At RT, there were a strong blue emission band (Es band) and a weak SA emission band.Fig. 2 showed the dependence of the near band edge emission of ZnSe epilayers on temperature in the range of 64-360K. It was found that the near band edge emission at 64K contained two emission bands, E band due to exciton-carrier interactions and P band caused by exciton-exciton interactions [13]. with increasing temperature, both E band and p band became undistinguishable. At 77K only one band (Es band) overlapping between the E and p band was detected in this emission region. with temperature further increased, the structurelless emission band widened and shifted towards long wavelength, and finally formed blue emission band at RT (Es band). This suggested that the Es band was related to free exciton emission.Fig. 3 showed the dependence of the intensity of near band edge emission of No.85-24 ZnSe epilayer on temperature. Near RT, the activation energy was about 19meV (Fig. 3 ) which was in agreement with the dissociated energy of free excitons in ZnSe crystals [13] . This means that free excitons are responsible fcr the Es band. As the excitation density was increased, the Es band widened and its peak positon shifted towards lower energy as shown in Fig. 4 and Fig. 5 . It was also found in Fig. 4 that with increasing excitation density, the intensity ratio of E’s band to SA emission band increased. It should be noticed that these behaviours of Es band at RT was very similar to that of E’s emission band at 77K, as shown in Fig. 6 . with excitation density increased the width of Es band became wider and its peak position shifted towards longer wavelength at 77K. It was also found in Fig. 6 that the intensity ratio of Es band which was caused by exciton recombinations to FB band which was due to free-to-bound transitions increased with increasing excitation intensity. Under high excitation density (I=0.16-1.7 I0 in Fig. 6 ) the ratio became decreasing with increasing excitation density. We showed in our recent work[13] that at low excitation level (I=0.01-0.16 I0), the Es band was mainly caused by exciton-carrier interactions. When the excitation density further increased, the exciton-exciton interactions appeared. The Es band was the overlapping of the E and p band at high excitation level. Because of the similarity between E’s band at RT and Es band at 77K it is reasonable to conclude that the E’s band was contributed by the scattered free exciton recombinations. The dissociation energy of free exciton of ZnSe is about 20meV[14], at RT many excitons were dissociated. Thus the possibility of exciton-exciton interactions was relatively small. That is why we couldn’t observe the intensity ratio of E’S band更多还原