Doping Behavior Of Semi-insulating GaAs By Neutron Transmutation

The neutron transmutation doping (NTD) in semiconductors is a very useful technique for the controlled impurity doping concentration by nuclear transmutation and homogeneous defect production because of the strong penetration of neutrons into materials. It is the practical application of neutron physics and technology to semiconductor materials science.In this thesis, we outline the principle of the NTD-Si, and compare with the characteristics of GaAs and Si. We give an account of the development of the NTD-GaAs, and point out the existent questions in research. We discuss the transmutation doping behavior of SI-GaAs by the thermal neutrons and the resonance neutrons (n, y) reactions, the reactions of fast neutrons of a reactor, and the reactions of 14 MeV fast neutrons of a neutron generator.It was obtained that a factor of the (n, y) reactions transmutation doping is a function of the effective neutron temperature, the ratio of the epithermal to the thermal flux of neutron, the thermal neutron cross section, and resonance integral. The neutron macroscopic cross section is imported in calculating doping concentration, we have found the relationship between the factor and neutron macroscopic cross section, and obtained the doping concentration expressions of ⁷⁰Ge, ⁷²Ge, ⁷⁶Se, ⁷⁶Ge, and ⁷⁰Zn because of the SI-GaAs (n, y) reactions transmutation. In different irradiated conditions, the factor is not fixed value that was about 0.16 cm^-1, because that during the calculation of cumulative cross section of ⁷¹Ga(n, γ)⁷²Ga, the ⁷¹Ga(n, γ)^72mGa reaction cross section was not included, that the resonance integrals of epithermal neutron were not included in the transmutation doping calculation, that effective neutron temperature was not calculated.Measuring reaction number of the ⁷⁵As(n,2n)⁷⁴As reaction and the doping concentrations of ⁷⁴Ge_As and ⁷⁴Se_As, we point out it is capable that the reactions for (n, 2n), (n, p), (n, α), (n, n' α) of ⁶⁹Ga,⁷¹Ga and ⁷⁵As in SI-GaAs induced by the reactor fast neutron. Because of those reactions, there are ⁶⁶Zn, ⁶⁷Zn, ⁶⁸Zn, and ⁶⁵Cu in NTD-SI-GaAs. The Ge impurities, when GaAs samples are irradiated with fast neutrons, come from the β^- decay of ⁷⁰Ga and ⁷²Ga and the electron capture of ⁷⁴As that are the products of ⁶⁹Ga(n, γ )⁷⁰Ga, ⁷¹Ga(n, 2n)⁷⁰Ga, ⁷⁵As(n, α)⁷²Ga, and ⁷⁵As(n, 2n)⁷⁴As, respectively. We are certain of being Cu in fast neutron irradiated SI-GaAs. The Ge_As defect impurities come from the interrelated neutron nuclear reactions of ⁷⁵As. The phenomenon of metal-like plasma resonance in fast neutron irradiated GaAs likely due to the vibration structure of Cu and Zn complexes in GaAs.We advance the principle and means of measuring the 14MeV neutron macroscopic cross section of SI-GaAs. Macroscopic cross sections of ⁷⁰Ge impurities for ⁷¹Ga(n, 2n)⁷⁰Ga and ⁶⁹Ga(n, γ)⁷⁰Ga reactions transmutation have been measured in the neutron energies of 13.5-14.7 MeV using the activation technique. Macroscopic cross sections of ⁷²Ge impurities for ⁷⁵As (n, α)^72m+gGa and ⁷¹Ga (n, γ)^72m+gGa reactions transmutation have been measured. Macroscopic cross sections of ⁷⁴Ge and ⁷⁴Se impurities for ⁷⁵As(n, 2n) ⁷⁴As reaction transmutation have been measured. Macroscopic cross sections of ⁷⁶Se impurities for ⁷⁵As(n, γ)⁷⁶As reaction transmutation have been measured. Using the experimental data of ⁶⁹Ga(n, 2n)⁶⁸Ga and ⁷¹Ga(n, n'α)⁶⁷Cu reaction cross sections were measured by Lanzhou University andthe cross sections evaluated data of 69Ga(n, a^Cu, 71Ga(n, a)68Cu and 69Ga(n, n'a)65Cu reactions are taken from IAEAND, macroscopic cross sections of ^Zn, 67Zn, 68Zn and 65Cu impurities have been calculated, respectively. Total factor of the HMeV neutron transmutation doping SI-GaAs is in range 36.901⁴6.241(10'3 cm"1), and the transmutation doping factor of Ge, Se, Zn and Cu impurities are in 19.450-25.035, 6.497-7.644, 10.937-13.531 and 0.02O-O.031 (10° cm'1), respectively, and Ge, Se, Zn and Cu ratio abort is (3-3.3): 1 : (1.7-1.8): (0.003-0.004).In this thesis, we have solved the problem on calculating to transmutation doping concentration of the (n, 7) reactions, if fast neutron transmutation doping, and if Cu being in NTD-GaAs. We advance a new explaining the mechanism of the GeAs defect impurities produce, and find reason on phenomenon of metal-like plasma resonance in fast neutron irradiated GaAs. In order to providing the theoretical and experimental evidences, the mechanisms of SI-GaAs neutron nuclear reactions and decay of the products were systematically discussed, and reaction number for 75As (n, 2n)74As and the doping concentrations of 74GeAj and 74SeAs and macroscopic cross sections of the transmutation doping Ge, Se impurities were measured, respectively, and macroscopic cross sections of ^Zn, 67Zn, 68Zn and 65Cu impurities have been calculated, respectively. Our results are expected to play a positive role in the research of the neutron transmutation doping of SI-GaAs semiconductor material, the research of semiconductor components characteristic change of GaAs.