A contribution to the study of the electronic properties of doped silicon at low temperature by nuclear magnetic resonance experiments

Contribution à l'étude par résonance magnétique des propriétés à basse température du silicium fortement dopé

Denis Jerome (1)

1 LPS - Laboratoire de Physique des Solides

When charge doping is introduced into pure silicon an insulator to metal transition occurs when the mean distance between monovalent atoms (phosphorus, arsenic,..) in case of donor doping decreases. This is a particular case of the Mott transition in a random system. The transition is investigated in this work using both electron nuclear double spin resonance (ENDOR) and 29Si nuclear spin resonance on both sides of the critical donor concentration determined to be Nc ≈ 2x1018 P per cc. The value of the exchange integral J between pairs of donor centers in silicon has been investigated by looking at the ENDOR spectrum of phosphorus-doped silicon in a range of concentrations of the order of 8x1016 per cc. The microwave field is saturating the cluster electronic line. The line shape of these ENDOR lines gives an unambiguous determination of the sign of this exchange integral which turns out to be antiferromagnetic. It is also possible to determine an order of magnitude of J and to have an idea about its distribution for two samples. We are able to understand all the features of the ENDOR spectrum at least in a qualitative way by calculating all the energy levels using a second-order perturbation calculation. A line coming from an ionized phosphorus center, weakly coupled to a pair of neutral phosphorus is also identified. The nuclear relaxation of 29Si in phosphorus-doped silicon is studied from the metal-nonmetal transition point of view namely the meta - nonmetal Mott transition in a disordered system. Going from the nonmetal to the metal there is a rapid decrease of relaxation time at the transition, donor impurity =1018 P atoms/cc. For the insulating side of the transition the dominant process of relaxation is due to the modulation of the dipolar interaction between the impurity electron spin hopping from one impurity center to another, and the nuclear spins. This type of relaxation can only take place if the material is compensated. For the metallic side of the transition the dominant process of relaxation is due to the modulation of the hyperfine coupling between the nuclei and the highly degenerate electron gas in a narrow band distinct from the bottom of the conduction band of width ≈ 19K with important correlations effects. The electron density in the vicinity of the donor centers is measured in a 2.5x1018P atoms/cc sample. The measurement shows that the electron remains strongly localized around the impurities. A comparison is made of our results with the D- band model of conductivity. It is expected that this work will contribute towards understanding mechanism of the Mott transition in correlated random systems.

Ce travail a pour but l'étude de la transition de Mott dans le silicium dopé au phosphore (ou à l'arsenic) au moyen de la double résonance électron-noyau et de la résonance nucléaire du Si29.

Mots clés: Doped silicon; Mott transition in random systems; Correlated electron gas.

Mots clés: Silicium dopé; Transition de Mott dans les systèmes désordonnés; Electrons fortement corrélés

Domaines: Electrons fortement corrélés [cond-mat.str-el]; Science des matériaux [cond-mat.mtrl-sci]

Denis Jerome. Contribution à l'étude par résonance magnétique des propriétés à basse température du silicium fortement dopé. Electrons fortement corrélés [cond-mat.str-el]. Université Paris Sud - Paris XI, 1965. Français. ⟨NNT : ⟩. ⟨tel-00848614⟩