J. M. Meese

A Review of Transmutation Doping in Silicon

The neutron transmutation doping (NTD) process in silicon is based upon nuclear reactor thermal neutron irradiation which induces the neutron capture reaction 30Si (n,¿) 31Si ¿ 31P + ß-. The transmutation product, phosphorus, becomes electrically active after suitable annealing of the accompanying radiation damage which is caused by a number of displacement processes. Because of the superior doping homogeneity which results from the NTD process, a number of device applications have evolved resulting in a significant fraction of the worlds float zone being neutron doped. This paper will present a review of basic research and production techniques which have evolved at MURR as a result of work associated with this new radiation effects technology.

Raman scattering from amorphous zones in neutron irradiated silicon

Abstract A Raman scattering study of neutron irradiated silicon is presented for the first time. We have observed features in the Raman spectrum arising from amorphous zones produced in the bulk of the sample due to neutron induced defects. We relate these first order Raman modes to the crystalline vibrational density of states averaged over the Brillouin zone.

Pressure studies of impurity levels in AlxGa1−xAs

The authors present a study of the deep and shallow donor levels under hydrostatic pressure. The shallow levels follow the conduction bands, while the deep levels are strongly sublinear with pressure. The temperature dependence of the intensities and energies is used to obtain an energy level diagram of the deep levels at high pressures.

Defect Production During Neutron Doping of Si

It is of interest to observe and classify the various defects which exist immediately after irradiation since it is at this point that differences in the neutron energy spectra of different reactors are most apparent. We will discuss methods of estimating the displacement rate at which Si atoms are dislodged from their normal lattice sites during a neutron irradiation induced displacement cascade. We also will present the results of a variety of measurements using EPR, optical absorption, Raman scattering and DLTS which have been used to observe a number of defects which have been produced in Si by room temperature neutron irradiation. The numbers of displacements observed by these techniques will be compared to a simple Kinchin-Pease cascade model.1–3

Reduction of α-particle sensitivity in dynamic semiconductor memories (16K d-RAMs) by neutron irradiation

Trace radioactive impurities found in all semiconductor devices induce soft errors in semiconductor memories by α-particle emission. Data taken on 16K d-RAMs which have been fast neutron irradiated to fluences from 1013 to 1016 n/cm2 show that soft errors in these devices can be significantly reduced while maintaining acceptable device operation. Reduction in soft error rate by factors as high as 80 are observed following irradiation and thermal annealing. The effect on device parameters is discussed as well as the defects responsible for this beneficial radiation processing. Estimates of the soft error rate improvement to be expected on higher density memory devices (64K and 256K d-RAMs) will also be presented.

A Detailed Annealing Study of NTD Silicon Utilizing Raman Scattering

The technique of Neutron Transmutation Doping (NTD) of a silicon crystal by an in-situ transmutation of the 30Si isotope into 31P via the reaction 30Si (n,γ) 31Si → 31P + β- has distinct advantages over conventional doping schemes. Among these are the precise ability to control doping concentrations and the overall uniformity of doping. The fast-neutron component of the reactor spectrum produces damage in the crystal which can be repaired by an annealing process.

Annealing mechanisms in neutron-irradiated silicon

Abstract Through a detailed annealing study of neutron-irradiated silicon, utilizing Raman scattering, several striking trends have been observed which lend themselves to an interpretation of the annealing mechanisms in the damaged material. Most notable of these observations is the fact that the Raman intensity appears to follow separate second-order decays in both the low (30–300°C) and high (350–600°C) temperature ranges, possibly indicating the uncorrelated nature of the combining defects. The low activation energies obtained (roughly 0.5 and 1.0 eV respectively), as well as the low attempt frequencies calculated (106s-1), suggest a rate-limiting step involving the ionization of a carrier from the defects. That the free carrier recovery of the extrinsic sample nearly parallels the defect annealing, tends to corroborate this point of view.