摘要
本文测量了经真空热处理的VPE ZnS_xSe_(1-x)(X=0.055,0.22)外延膜液氮温度下的光致发光(PL)光谱,观察到一个新的蓝色发光带,并把这一谱带归结为导带中自由电子与束缚在深受主中心上空穴的复合。实验表明,深受主中心是在真空热处理时形成,并与真空热处理时在外延层中产生的Zn空位有关。
There is considerable interest in luminescence of ZnSxSe1-x bluk crystals and epilayeis .P. K.Chatter jee et al.and M.Yamaguchi et al.observed a broad band (4700-4800A) in photoluminescence (PL) spectra in Aland Na-doped ZnSe at 4.2K and in Li- or Na-doped ZnSe at 90K, respectively, They attributed this band to D-A pair recombination and free to bound recombination, respectively.In this paper we leport that a broad band A was observed in PL spectra in vacuum heated VPE ZnSxSe1-x epilayers at LNT. The origin of the band A is discussed.VPE ZnSxSe1-x. epilayers used in this work were grown on (100) GaAs substrate with VPE method. Specimen was excited by 500W Hg arc lamp, PL spectra were measured using a grating spectromator of Model 44W with C31034 cooled photomultiplier.Fig.1(a) and (b) show the PL spectra in vacuum-heated and as-grown ZnS0.055Se0.94l epilayers at LNT, respectively. The bands E(442lA),FB (4570A),D1(5550A) and D2(6200A) in Fig.1(b) are often observed in PL spectra in ZnSxSe1-x. A broad band A is observed in PL spectrum in Fig. l(a). Fig.2(a) and (b) show the temperature dependence of intensities of A and FB bands, respectively. The thermal activation energy of A and FB bands is determined to be 0.253eV and 0.105eV, respectively. Comparing with the M. Yamaguchi's result, we consider that the origin of band A may be free to bound recombination. The acceptor ionized energies for bands FB and A are calculated to be 0.112eV and 0.232eV, lespectively. It is obvious that the acceptor for band A is deeper than that for band FB and the shallow acceptor for band FB may be Li(0.114eV) . The acceptor ionized energies for bands FB (0.112eV) and A(0.232eV) ate in agreement with the thermal activation energies of bands FB(0.105eV) and A(0.253eV),respectively. This result indentifies that band A could be ascribed to the recombination of free election with hole bound in deep acceptor.We also obseived broad bands A1 and A2 in PL spectium in vacuum headed VPE ZnS0.22Se0.78 epilayer at LNT,as shown in Fig.3(a). These broad bands may be associated with Zn vacancies.As shown in Fig.1(a),the intensity of band D1 increases after the specimen was heated in vacuum. We have known that yellow-green band is associated with Ga or Al-VZn pair and Ga or Al-Na pair.Zn vacancies could be produced by heating ZnSe in vacuum.According to the study on PL spectra in vacuum-heated ZnSe by X.W.Fan et al.,we consider that band D1 is also associated with Zn vacancies. Fig.5(b) shows the PL spectrum at LNT in ZnS0.055Se0.845 epilayer which was annealed in zinc atmosphere after being heated in vacuum. As shown in Fig.5(b), A and D1 bands disappear, E and FB bands appear again. This lesult supports that both A and D1 bands be associated with Zn vacancies.Fig.4(a) and (b) show the PL spectra in vacuum-heated and as-grown ZnS0.055Se0.945 epilayer at RT, lespectively. It is obvious that the exciton -related band E disappears in PL spectrum shown in Fig.4(a).In conclusion, broad band A at LNT could be attributed to free to bound recombination, this band is associated with Zn vacancies. It is important to avoid ZnSxSe1-x epilayers to be heated in vacuum in order to increase exciton emission of VPE ZnSxSe1-x epilayeis.
出处
《发光学报》
EI
CAS
CSCD
北大核心
1990年第2期90-95,共6页
Chinese Journal of Luminescence
基金
国家自然科学基金
