Nuclear magnetic resonance studies of II-VI and III-V semiconductor alloys

Abstract

In this thesis, I show how the basic solid-state NMR techniques can be used to study the local electronic structures of II-VI and III-V semiconductor alloys on an atomic scale. We have focused our studies on a few high quality samples, mainly Hg[1-x]Cd[x]Te in the II-VI group, In-based binary III-V bulk semiconductors InP, InAs and InSb, and the III-V alloys Ga[1-x]In[x]As. For solid-state-recrystallized device-quality bulk Hg[1-x]Cd[x]Te samples, with x equal to 0.2, 0.22 and 0.28, corresponding to the narrow-gap semiconducting side of the band-inversion configurations, we have obtained detailed band-edge symmetry information, and site-selective quantitative charge carrier orbital characteristics on an atomic scale. Our study also indicated that a random cation distribution model well described the materials. We have investigated 115In magnetic resonance frequency shifts and the temperature dependence of these shifts in In-based III-V binary semiconductors. We have extracted the chemical shifts from the total shifts for these III-V semiconductors at 303K and 77K. Our NMR study of these binary semiconductors not only enhanced the understanding of electronic properties of these compounds, but also served as a reference for our NMR studies of III-V alloys. We performed 115In NMR studies for dilute III-V semiconductor alloy Ga[1-x]In[x]As with x equal to 0.72%. Spectra clearly indicating the local electronic configurations were obtained. We carried out a series of field orientation studies, and determined the field gradient which is due to In-In pairs. This study provided evidence of local clustering of In atoms.