Characterization of Nitrogen Species for P-Type Doping of ZnSe
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S. MIWA', T. YASUDA"'), L.H. KUO' C.G. JIN '4, K. TANAKA'3,4) and T. YAO1' 3'53 1)Joint Research Center for Atom Technology, 1-1-4 Higashi, Tsukuba 305, Japan 2)Angstrom Technology Partnership, 1-1-4 Higashi, Tsukuba 305, Japan 3)National Institute for Advanced Interdisciplinary Research, 1-1-4 Higashi, Tsukuba 305, Japan 4)University of Tsukuba, 1-1 Tennohdai, Tsukuba 305,Japan 5)Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980, Japan
ABSTRACT Laser-induced fluorescence(LIF) spectroscopy has been applied to the detection of excited nitrogen molecules coming out of a plasma source used for p-type doping of ZnSe. With the use of a fluorescence-photon-counting system, the fluorescence of nitrogen molecules in the A3 Y u' (v=0) state was observed even in a high vacuum condition _ 10-4 Pa. The correlation between LIF intensity of nitrogen molecules in the A3 2 u+(v=O) state and the net acceptor concentration of nitrogen doped ZnSe epitaxial layers was investigated. INTRODUCTION Nitrogen plasma sources have been most frequently used to dope ZnSe into p-type by molecular beam epitaxy (MBE) [1-4]. So far, maximum net acceptor concentration has been limited to around lxl08cm3 in ZnSe [1,2]. One of the most important growth parameters is chemical species in the nitrogen plasma : excited neutral nitrogen and nitrogen ion. The control of these chemical species will bring about a new breakthrough for the doping of wide bandgap materials. However, there have been only a few studies for the characterization of chemical species produced by a nitrogen plasma used for MBE growth. The nitrogen plasma in a plasma cavity has previously been characterized by optical emission spectroscopy [2-5]. The purpose of this paper is to characterize and control the nitrogen species generated by a plasma source. We have characterized the nitrogen plasma coming out of a helicon-wave excited rf (13.56MHz) plasma source by laser-induced fluorescence (LIF) measurement and observed that nitrogen molecules in the Aý E u' (v=0) excited state are present in the region outside of the plasma source. The dependence of LIF intensity of nitrogen molecules in the A3 I u+(v=0) state and the net acceptor concentration of 51 Mat. Res. Soc. Symp. Proc. Vol. 406 ©1996 Materials Research Society
to Rotary pump
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Helicon-wave excited plasma source Excimer Laser -Dye Laser BBO XeCh:308nm
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PIN Diode
Laser beam HAMAMATSU C1083
\I_ N2 beam
Photodiode • • Boxcar Integrator EG&G 4400
• Photomultiple Tube PlanoAMAMATSU-R2949 S "• convex lens Trigger "• TMP Multichannel Scaler
fMutcanlSle to Rotary pump
EG&G MCS-Turbo
Fig.1 Experimental setup of LIF measurement. nitrogen doped ZnSe epitaxial layers on the rf power of the plasma source have been studied. The correlation between these dependence will be discussed. LIF MEASUREMENT OF EXCITED NEUTRAL NITROGEN Figure 1 shows the schematic diagram of the experimental setup of LIF measurement. The light source was an excimer pum
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