Date of Graduation

1999

Document Type

Dissertation/Thesis

Abstract

A detailed liquid-helium-temperature photoluminescence study has been performed on a series of ZnSe epilayers grown by molecular beam epitaxy. The samples were grown at West Virginia University and include undoped and nitrogen-doped epilayers (with different levels of doping). The PL has been studied as a function of excitation wavelength, power, temperature and time. Electron Paramagnetic Resonance (EPR) and Photoluminescence Excitation (PLE) were also performed. An ionization energy of 50 meV for the “deep” donor in a lightly doped ZnSe:N sample is determined using power dependence data. Heavily nitrogen-doped samples (≥8 x 1018 cm−3 ) provided evidence for a second deeper donor with an ionization energy greater than 100 meV. The importance of accounting for interference effects in the PL spectra from heavily-doped ZnSe:N is shown. A model is proposed to explain the PL and PLE results in the presence of potential fluctuation and the deeper donor. The PL spectra obtained from samples grown using two rf sources (Oxford and EPI) were compared. Although the EPI source produced a lower ratio of ions to atomic nitrogen, compensation is still a problem for heavily doped samples. A third band, at 2.66 eV, is observed under high-power pulsed excitation, and the presence of this band can be correlated with growth conditions. Under the same conditions, a bound exciton appeared in a heavily doped sample. The presence of this exciton, called the IV line, was attributed to Se vacancies in undoped ZnSe/GaAs. The EPR results indicate the presence of singly ionized selenium vacancies in our heavily doped samples, and they can play a role in compensation.

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