HIGH RESOLUTION STUDIES OF THE EXCITATION SPECTRA OF BERYLIUM AND MAGNESIUM DOUBLE ACCEPTORS IN GERMANIUM WITH AND WITHOUT UNIAXIAL STRESS (SPECTROSCOPY)

JOHN WILLIAM CROSS, Purdue University

Abstract

Substitutional Mg and Be impurities in Ge bind two holes and are solid-state analogs of neutral helium. A high-resolution Fourier-transform spectrometer, a liquid-helium cooled optical cryostat, and a liquid-helium cooled germanium bolometer were employed in the study of Ge(Mg('0)), Ge(Be('0)), and Ge(Be('-)) without stress and Ge(Be('0)) with uniaxial stress. The excitation lines of the neutral double acceptors represent one-hole excitations from the (GAMMA)(,8) x (GAMMA)(,8) = (GAMMA)(,1) + (GAMMA)(,3) + (GAMMA)(,5) (1s)('2) ground state to the (GAMMA)(,8) x (GAMMA)(,8)', (GAMMA)(,8) x (GAMMA)(,7)', and (GAMMA)(,8) x (GAMMA)(,6)' (1s) (np) excited states. The binding energies of the excited states show excellent agreement with those of other group-II and group-III accep- tors as well as with those calculated in the effective-mass theory of Baldereschi and Lipari. The spectrum of Ge(Be('0)) shows a doublet structure which can be attributed to the splitting of the ground-state multiplet. When Ge(Be('0)) is suitably compensated with a group-V impurity or with Li, the resulting Ge(Be('-)) exhibits lines in its excitation spectrum representing one hole transitions, the binding energies of the excited states being four times larger than those of neutral acceptors. The excitation lines of Ge(Be('-)) show the characteristic broadening and asymmetry caused by charged impurities. Under uniaxial stress the single hole (1s)('2) (--->) (1s) (np) excitation spectrum of Ge(Be('0)) shows splittings and polarization effects. These piezospectroscopic effects were observed for a compressive force, (')F, along 111 and along 100 . They are interpreted in terms of T(,d) site symmetry for the substitutional Be acceptors when unstressed and a deformation potential theory in which the phenomenological deformation potential constants characterizing the single hole states determine the behavior of the (1s)('2) as well as the (1s) (np) levels. The shear deformation potential constants have been deduced for the ground state and the excited state of the D transition. Pronounced level crossing effects manifest in the intensities of the G transition.

Degree

Ph.D.

Subject Area

Condensation

COinS