摘要
本文首次利用热激电流(TSC)法测量到两个出现于ZnS颗粒表面的陷阱能级(ΔEt_1=0.64eV,ΔEt_2=0.89eV),而且随着DCEL屏形成程度的提高(形成电压升高,形成时间延长),其表面陷阱的浓度将随之增大。我们认为,产生表面能级ΔEt_1和ΔEt_2的原因可能是由于形成过程中,Cu^+离子从ZnS颗粒表面迁移走后颗粒表面又吸附了不同的氧离子(O^-和O_2^-)所致。
In principle all atoms in a finite solid are in a surface region. However the precision of measurement of many 'bulk' parameters is such that the effects of the surface are below the limit of detection if thickness of the solid is more than a few tens of microns. Hence the effective surface region in practice is from a few atomic layers to several microns. (For insulators, the field from a surface charge can penetrate up to a few centimeters .) As we know, the mean particle size of powder DCEL phosphors is about 1-3μm. Therefore the surface effect on DCEL devices must be Very obvious. But there is no report on it up to now. In this work, Thermally Stimulated Current(TSC) method was used to study the surface state levels of DCEL panels, and two surface electron-trap levels were measured for the first time.After lots of TSC measurements, two TSC peaks were obtained (Tml = 50℃,Tm2=176℃) > which appeared gradually with, the increase of forming level of DCEL panels. In the same experimental conditions, the TSC spectrum of ZnS(Cu) powder phosphor panels (without Mn2+ and Cu+ ions doped, only copper coated on ZnS surface) is almost the same as ZnS:Mn, Cu(Cu) DCEL panels [Mn2+] - 5 ×10-3g/g, [Cu+] = 4 ×10-4g/g, and their peak positions (Tm2 and Tm2) keep unchanged with the change of doped Mn2+ and Cu+ ion concentrations.In general, when TSC method is used to measure deep levels in semiconductors, Tm increases with increasing the warm-up rate, β. But here for DCEL panels, Tm1 and Tm2 all get decreased with the increase ofβ.This abnormal phenomenon is possibly caused by so-called Thermally Stimulated on Emoelectron Emission (TSEE) on ZnS surface in the linear warm-up process of powder DCEL panels. From the experimental facts aforementioned, it can come to conclution that the two deep energy levels (Et1 = 0.64eV, Et 2 = 0.89eV) which are corresponding to Tm1 and Tm2 do not exsist in ZnS particle bodies, but only on the surfaces, i.e., they are surface state energy levels of DCEL panels.In our opinion, the appearance of the two surface energy levels (Bt1 and Et2) are mainly caused by adsorption of oxygen ions (O~ and O2-) on ZnS surface, just as the behavior of the adsorption of oxygen ions on ZnO surface . Because the electron affinity of oxygen and ozone is very strong,stable and strong bond can be formed when the oxygen is adsorbed on the surface of semiconductors. Here, in powder ZnS:Mn, Cu DCEL panel system, the panel forming process is operated in open air or in damp-proof molecular sieve, where the partial pressure of oxygen Po2 is much higher than 10-6mmHg; and the surface of ZnS particles gradually get to be 'nude' after Cu+ ions migrate away from the surface of ZnS particles. So it is entirely possible that the oxygen is adsorbed on the 'nude' ZnS surface.The higher the forming level of DCEL panels,the more the oxygen adsorbed on the surface of ZnS. As a result, the surface concentration of electron traps of ZnS is increased gradually. And it can greatly influence on the photoelectric characteristics of DCEL devices.
出处
《发光学报》
EI
CAS
CSCD
北大核心
1989年第4期283-289,共7页
Chinese Journal of Luminescence
