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Title: A nuclear magnetic resonance study of tellurium doped gallium phosphide
Author: Rogerson, A.
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 1975
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A study has been made of 7, LEC grown, tellurium doped gallium phosphide samples using pulsed nmr, Hall effect, and related measurements. The results have been correlated with nmr, esr, electron susceptibility, and transport measurements in similar systems, and changes which occur in the donor electron system in the intermediate doping region preceding the metallic transition have been discussed. The effects which these changes have on the nuclear relaxation times of the host nuclei have been discussed in terms of the various stages of nuclear relaxation by spin diffusion to paramagnetic impurities. In the lightly doped samples, rapid diffusion and diffusion limited relaxation processes have been identified around the minima in the T1:T curves of the P31 , and two Ga isotopes respectively. The effects on nuclear relaxation of the preferential distribution of the Te donor wavefunction on P31 sites have been discussed. Experimental calculations of the Ga69 and Ga71 spin diffusion coefficients have been made and compared with values derived from spin diffusion theory. T1 results from the more heavily doped samples have been discussed in terms of the various models of the state of the electron system in the intermediate doping region. Evidence of the increasing importance of electron spin-spin interactions and diffusion vanishing relaxation processes have been obtained from the concentration, magnetic field, and temperature dependences of the T1's of all three isotopes at low temperatures. Hall and conductivity measurements reflected the reduction in donor ionisation energy with increasing donor concentration in the intermediate doping region, and the observed movement of the position of the T1 minima to lower temperatures in the same samples have been taken as further evidence of this effect. Calculations of the donor ionisation energy have been made from analysis of the temperature dependence of the Ga69 and Ga71 T1's around the T1 minima and from the variation of the position of the minimum with frequency. The weakening and eventual disappearance of the T1 minima in the most heavily doped samples have been discussed in terms of the reduction in the effectiveness of nuclear relaxation to single paramagnetic impurities as impurity hopping and spin-spin effects increase. The enhanced magnetic field dependence and increase in T1 observed in the most heavily doped samples at low temperatures have been taken as evidence for the incomplete delocalisation of the donor electron system in these samples.
Supervisor: Tunstall, David Prestwich Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QD181.G2R7 ; Gallium