摘要
本文首次在77K温度的电致发光光谱上,观测到了自由激子和自由激子(E_x-E_x)散射的发射带P。根据半经典理论,得到CdS单晶在高激发密度下的激子有效温度高于晶格温度。并且在77K温度下,通过氮分子激光器3371(?)谱线的激发,观察到了E_x-E_x散射的P带的受激发射现象。
Some papers have been published on luminescence of free exciton under high density excitation in CdS. But most of the research about exciton-exciton interaction are concentrated on photoluminescence below 77K. So far no report is found on free exciton emission in forward biased CdS MIS diodes with high pulse current density.Undoped CdS crystals were grown by sublimation in our labora tory.Dice with dimensions of 5×2×1mm3 were annealed in molten cadmium at 650℃ to reduce their resistivity to the range of 0.1-5.cm. The MIS structure was prepared by making an ohmic contact on the substrate and evaporating an insulating layer and Au contact on the opposite surface. PL and EL were excited by 3371A line of a pulsed nitrogen laser or by the pulse with high current density.In this paper, we describe free exciton emission in CdS crystals under high excitation of 3371A line of a pulsed nitrogen laser or by the pulse with high current density, we found a new emission band P(4950 A) as shown in Fig.1 and Fig.2. With increasing excitation density, the dependence of P band intensity I on excitation intensity J can be expressed as the superlinear relation. Fig.4 shows the stimulated emission of P band spectra of CdS at 77K at different excitation levels by 3371A line of a pulsed nitrogen laser.One of the most interesting aspects of the work concerns the nature of P band in EL and PL in CdS. Saito et al. proved that P band they observed in the temperature range of 8--65K in PL is produced by the inelastic collision process of two excitons, and pointed out that the effective temperature of free exciton is higher than the lattice temperature. According to the semi-classical therory of Gross et al the shape of the Ex-2LO band is discussed for CdS MIS diodes at 77K with current density of 350mA/mm2. In this case the effective temperature of free exciton is about 120K. The fact mentioned above proves that the P band obtained in CdS crystals is produced by Ex-Ex interaction.Shaklee believe that the stimulated emission intensity depended on the length of excitation, as indicated in formula (2),and a linear region in a semi log-plot was a direct indication of the existence of gain. Fig.7 shows emission intensity I of P band measured in Fig.4 as a function of excitation length for three different pump powers. These results demonstrate the existence of stimulated emission.We report the observation of the Ex-Ex scattered emission in EL in CdS MIS diodes for the first time. The result of this paper indicates that it is probable to produce the Ex-Ex stimulated emission in EL in CdS MIS diodes by increasing the pulse current density.
出处
《发光学报》
EI
CAS
CSCD
北大核心
1990年第4期256-263,共8页
Chinese Journal of Luminescence
基金
国家自然科学基金资助课题
