Transmutation Doping of III-Nitrides
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dope AN have not been found.' Under many conditions of growth and doping AIN remains an insulator with resistivity of 109 to 1012 fcm.1 Ion implantation can be a useful method of GaN doping. Since p- and n-type, and also highly resistive layers, have been realized, the method can be used to fabricate of allimplanted devices. 5 ' 6 However, much more research should be done to achieve good reproducibility. Transmutation doping is used industrially for obtaining n-type silicon. Samples of pure Si are irrAdiated with neutrons in nuclear reactors. One of the isotopes of Si can absorb thermal neutrons and undergo subsequent 03-decay. As a result, Si transmutes into phosphorus. The material is then annealed for healing the radiation damage related to the unavoidable presence of fast neutrons. It is possible to control precisely the concentration of P atoms by controlling the neutron fluence. Transmutation of B into Li was studied for diamond doping 7,8 and showed promising results. Data on relevant transmutation reactions for AN, GaN and InN are given in Table L Nitrogen has a very small cross section of neutron absorption. Even if it absorbs a neutron, it changes into another stable isotope of N. Transmutations of Al, Ga and In occurs with the absorption of a neutron and subsequent J3-decay, except for a weak channel of transition of In into Cd, when the neutron absorption is followed by the capture of a K-
519 Mat. Res. Soc. Symp. Proc. Vol. 572 ©1999 Materials Research Society
shell electron or by the emission of a positron. 9'10 Absorption of the neutron puts the mother nucleus in an excited state, from which it decays with a certain half life, given as tl/2 in Table I. In all cases given in Table I, the daughter isotopes are stable. The last column in Table I gives the concentration of the transmuted atoms Nt for one hour of neutron irradiation at a thermal neutron flux of 1013 cm 2 s1. a) It was calculated through the relation: Nt = N a s F t where N is the concentration of mother atoms, a is the isotopic abundance of those atoms, S is the cross section for neutron capture (averaged over thermal neutron spectrum), F is the thermal neutron flux, t is the irradiation time. Table I. Data on transmutation by neutron capture of Si, A], Ga and In 1 Mother Nucleus (Z, m) Si (14, 30) Al (13, 27)
Abund ance (%) 3.1 100
Cross Section (barn) 0.11 0.23
Daughter Nucleus (Z, m) P (15,31) Si (14, 28)
Ga (31, 69) Ga (31, 71) In(49, 115) In (49, 115) In (49, 113)
60.1 39.9 95.7 95.7 4,3
1.8 0.15 72 42 3
Ge (32, Ge (32, Sn(50, Sn (50, Sn (50,
In (49, 113)
4.3
0.16
Cd (48, 114)
70) 72) 116) 116) 114)
t1/ 2
Energy (MeV)
1.49 2.6h 2.82 2.3 min 21 min 1.65 14.1 h 1.5-3.15 54min 0.6-11.6 3.3 14s 1.2 -kV min -kV 49.5 days
Nt in I h (cm 3 ) 4.5x1012 4.Ox 1014 1.6x10' 5 1.OX1014 1X1016 0.94x1016 3.0×x1O
3
0.16x1013
Z is the atomic number, m is the atomic mass, cross sections are in barns (1 barn = 10-24 cm 2). Concentrations of atoms 3 used in the calculation: N(Si) = 0.37x 1023 cm N(Al) = .48x1023 cm-33 N(Ga) = 0.43x
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