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Excitation spectra of magnesium impurities diffused into undoped silicon as well as into silicon doped with group-III acceptors have been measured. In the former, magnesium is a heliumlike neutral donor (Mg ) with excited states similar to those of group-V donors and close to the effective-mass positions; its ionization energy at liquid-helium temperature is 107.50 +0.04 meV. In specimens containing group-III impurities, with the magnesium partially compensated, excitation spectra are observed similar to those of group-V donors and that of Mg except that the spacings between corresponding lines are approximately four times larger and the 1s(hl) -2p~t ransition is a closely spaced doublet, 0. 2 meV apart. These features are consistent with a singly ionized heliumlike magnesium donor (Mg') and a small chemical splitting of the 2p~state; the ionization energy is 256. 47+0. 07 meV at liquidhelium temperature.The excitation spectrum of Mg' was also observed in specimens containing Mg subjected to high-energy electron irradiation. Study of the piezospectroscopic effects shows that both Mg and Mg' occupy a 7&-symmetry site with ls(A. &) as the ground state. A value of 8. 7 +0.2 eV has been deduced for the shear-deformation-potential constant -"of the (100) conduction-band minima of silicon.

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Magnesium has been introduced into silicon containing oxygen by diffusion. The low-temperature absorption spectrum observed clearly demonstrates that magnesium can pair with oxygen to form magnesium±oxygen complex impurities in silicon. Similar to an isolated magnesium donor, the magnesium±oxygen complex is also an interstitial donor in silicon. The ionization energy of neutral magnesium±oxygen complex donor is 124.66 meV, which indicates that it is a slightly deeper donor compared with neutral magnesium impurity in silicon. L. T. HoFig. 1. Low-temperature absorption spectrum of silicon containing magnesium and oxygen. Liquid helium was used as coolant

Spin-exchange optical pumping (SEOP) has 12 been widely used to produce enhancements in nuclear spin 13 polarisation for hyperpolarised noble gases. However, some 14 key fundamental physical processes underlying SEOP 15 remain poorly understood, particularly in regards to how 16 pump laser energy absorbed during SEOP is thermalised, 17 distributed, and dissipated. This study uses in situ ultra-low 18 frequency Raman spectroscopy to probe rotational temper-19 atures of nitrogen buffer gas during optical pumping under 20 conditions of high resonant laser flux and binary Xe/N 2 gas 21 mixtures. We compare two methods of collecting the Raman 22 scattering signal from the SEOP cell: a conventional 23 orthogonal arrangement combining intrinsic spatial filtering 24 with the utilisation of the internal baffles of the Raman 25 spectrometer, eliminating probe laser light and Rayleigh 26 scattering, versus a new in-line modular design that uses 27 ultra-narrowband notch filters to remove such unwanted 28 contributions. We report a *23-fold improvement in detection sensitivity using the in-line module, which leads to faster data acquisition and more accurate real-time monitoring of energy transport processes during optical pumping. The utility of this approach is demonstrated via measurements of the local internal gas temperature (which can greatly exceed the externally measured temperature) as a function of incident laser power and position within the cell.

Previous study indicates, that magnesium, when diffused into silicon, can pair with dispersed oxygen in the crystal to form magnesium -oxygen complex impurities. Recently, we have successfully introduced magnesium into silicon containing oxygen as well as group-III impurities. We have observed for the first time the excitation spectrum of singly ionized magnesium -oxygen complex impurities, which clearly demonstrates that magnesium -oxygen complex impurity is a double donor in silicon. Our experimental result also shows that the ionization energy of singly ionized magnesium-oxygen donor is 274.90 meV, which is slightly larger compared with that of singly ionized magnesium donor in silicon.Introduction It is well known that magnesium, when diffused into silicon, is in the interstitial position and behaves as donor impurity. Since magnesium is a group-II element, its two 3s valence electrons can all be donated as donor electrons. From the excitation spectra observed for both neutral and singly ionized magnesium donor impurities in silicon, it is clear that magnesium is a double donor in silicon [1].Further study has shown that the interstitial magnesium can also pair with dispersed oxygen, if presented in the crystal, to form magnesium-oxygen complex impurities in silicon [2]. The lowtemperature absorption spectrum observed clearly indicates that such magnesium -oxygen complex impurities, similar to isolated magnesium donor impurities, are also interstitial donors in silicon. The ionization energy of neutral magnesium -oxygen complex donor has been obtained to be 124.66 meV indicating that the neutral magnesium -oxygen complex donor is a slightly deeper donor compared with neutral magnesium impurity in silicon.Recently, we have successfully observed the excitation spectrum for singly ionized magnesiumoxygen complex impurities in silicon. Our observation clearly demonstrates that the magnesiumoxygen complex donor, similar to isolated magnesium double donor, behaves as a double donor in silicon as well. The purpose of the present paper is to report our experimentally observed results on this matter.

Local conductivity and surface photovoltage variations due to magnesium segregation in p-type GaN

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