The Study of Contamination of Carbon, Boron, and Oxygen in LEC-GaAs
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THE STUDY OF CONTAMINATION OF CARBON,
BORON, AND OXYGEN IN LEC-GaAs
Y. Itoh, M. Takal*, H. Fukushima*, and H. Kirita* The Institute of Physical and Chemical Research, Hlirosawa, Wako, Saitama 351-01, Japan *Faculty of Engineering Science, Osaka University, Toyonaka, Osaka 560, Japan "**Japan Analysis Center, Sannou, Chiba 281, Japan ABSTRACT Carbon in LEC GaAs was found to be introduced as CO from the ambient atmosphere; the oxygen concentration in the crystals decreased with increase in the duration of melting. An equilibrium segregation coefficient of oxygen in GaAs crystals was found by charged particle activation analysis to be 0.1, the value of which was smaller by a factor of 3-4 than that reported before. INTRODUCTION It is important to control and suppress residual impurities such as carbon, boron and oxygen in a LEC-GaAs crystal[l]. To date, however, the role of such impurities in the crystal has not been clarified because of the lack of accurate and precise analytical methods for the determination of such impurities. In this study, the concentrations of carbon, boron and oxygen in LEC(Liquid Encapsulated Czochralski)-GaAs by a newly modified CPAA(charged particle activation analysis) method[2,31. In the case of the LEC method, usually, the molten GaAs is covered with a boric oxide encapsulant in pyrolytic BN crucible, and heated by a graphite heater. In this case, carbon, boron and oxygen get into or out of the GaAs melt, and are not segregated into the GaAs crystal according to the normal freezing process. Therefore, it is difficult to estimate the behavior of these impurities, such as segregation during LEC processes. However, the segregation behavior of carbon, boron and oxygen is important to control these concentrations in LEC GaAs crystal. We Investigated the incorporation of carbon and the equilibrium segregation coefficients of carbon, boron and oxygen in the 12 13 GaAs crystal. The reactions used were C(d,n) N, natB(d,xn)llC and 16 0( 3He, p) 1 8 F for carbon, boron, and oxygen, respectively. EXPERIMENTAL PROCEDURES Sample preparation The samples used were LEC-GaAs crystals pulled from a melt of 99.99999 % arsenic and 99.9999 % gallium in a pyrolytic BN(boron nitride) crucible. Three different parameters were used under following conditions : different ambience of CO concentrations; different melting durations; for segregation coefficients, the GaAs ingot was cooled down rapidly at the solidified fraction of 0.5 and cut from the tail portion of the GaAs single crystal ingot and the remainder. Samples were cut in the shape of rectangular 3 plates (20 x 20 x 1 mm ), and the surfaces of their planes were mirror-polished. Establishment of Conditions in C, B and 0 Analysis
Mat. Res. Soc. Symp. Proc. Vol. 163. 'c1990 Materials Research Society
1002
Samples were bombarded for 10 min with a deuteron beam (8 MeV, 5 itA) 3 gA) for carbon and boron, and 60 min with a helium( He++)beam (12 MeV, 5 for oxygen from the cyclotron at the Institute1 3 of Physical and Chemical 12 C(d n) N (9.98 min half life)
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