The behavior of the CH3 radical density in a parallel-plate RF CH4 plasma diluted with rare gases (He, Ne, Ar, Kr, and Xe) was investigated systematically using infrared diode laser absorption spectroscopy. The CH3 radical density increased in CH4/Xe and CH4/Kr plasmas with increasing rare gas dilution. The Xe* atom densities in the lowest metastable state 3
P
2 and the resonant state 3
P
1 were measured in CH4/Xe plasma through absorption spectroscopy using a Xe hollow cathode lamp in order to clarify the role of Xe* (3
P
2 and 3
P
1) atoms. It was shown that the increase in the CH3 radical density in CH4/Xe plasma was mainly caused by the collision of Xe* atoms with CH4 molecules.
Both the CH3 radical density and carbon thin-film formation were investigated in an RF-discharge CH4/H2 plasma. In this plasma, although CH3 radical density was almost constant, the deposition rate decreased markedly with increasing H2 partial pressure. These results suggested that the surface loss of the radicals was decreased due to the change in surface composition of the film, and also the film etching was enhanced with increasing H2 partial pressure. Therefore, the deposition rate of the carbon thin film decreased.
The CH3 radical density and the deposition rate of carbon
thin film were measured under the same conditions in RF-discharge CH4 and
CH4/rare gas plasmas. The behavior of the CH3
radical density showed a similar tendency as the deposition rate
of carbon thin film as a function of power and CH4 pressure
in CH4 plasma. In CH4/Xe plasma, where a selective formation mechanism
increases the CH3 radical density with increasing Xe dilution whereas other
CH
x
radicals are expected to decrease, the carbon deposition rate
increased with increasing Xe dilution. These results strongly suggest
that the CH3 radical is the dominant precursor in the film formation.
The increase of film formation rate in CH4/Xe plasma was slower than
that of the CH3 radical density with increasing Xe dilution. This could
be attributed to the sputtering of the film by heavy Xe ions.
In CH4/He plasma, where the effect of sputtering is expected to be small,
the film deposition rate and the CH3 density varied in a much more
similar manner.
ZnS:Tm and ZnS:Tm,Cl thin films were grown by metalorganic chemical vapor deposition (MOCVD), using diethylzinc, H2S, Tm(thd)3 (thd=2,2,6,6-tetramethyl-3,5-heptanedione), and HCl. The ZnS:Tm did not contain oxygen which might be introduced through the thd-radical. It thus has only codopant-free Tm3+ luminescent centers probably associated with native defects. The electroluminescence (EL) spectrum of the ZnS:Tm,Cl showed three satellite emission lines in addition to the original emission of the ZnS:Tm, indicating the existence of Tm–Cl complex centers. In contrast, the photoluminescence (PL) spectrum of the ZnS:Tm,Cl under host excitation showed no discernible satellite emission lines. Hence, though the Tm ions in the Tm–Cl complex centers are expected to be charge compensated by Cl or a certain Cl-induced defect, they are rather inactive in the PL excitation while active in the EL excitation. The same properties were observed for the MOCVD-grown ZnS:Sm and ZnS:Sm,Cl [A. Kato, M. Katayama, A. Mizutani, N. Ito, and T. Hattori, J. Appl. Phys. 77, 4616 (1995)], and therefore they probably occur for other rare-earth luminescent centers with Cl codopant.
ZnS:Sm, ZnS:Sm,Cl, and ZnS:Cl thin films were grown by metalorganic chemical vapor deposition using the thd-chelate (thd=2,2,6,6-tetramethyl-3,5-heptanedione) of Sm and hydrogen chloride. The electroluminescence spectrum of the ZnS:Sm,Cl showed three satellite peaks appearing in each of the 7 nm ranges around the three dominant peaks that the ZnS:Sm has originally. The ZnS:Sm,Cl also showed photoluminescence attributed to the self-activated centers, but its intensity was less than 10−2 of that of the ZnS:Cl. The effect of the Cl codoping on Sm3+ luminescent properties is discussed on the basis of the Sm-VZn (zinc vacancy)-Cl complex formation.
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