Optical spectroscopy of acceptors in semiconductors: I. Acceptor complexes in neutron transmutation-doped silicon. II. Piezospectroscopy of beryllium double acceptors in germanium

Charles Raymond LaBrec, Purdue University

Abstract

Substitutional group III impurities in group IV elemental semiconductors bind a hole from the valence band and are solid-state analogs of the hydrogen atom; likewise, group II impurities bind two holes and are analogs of the helium atom. In these materials, the electronic transitions from the acceptor s-like ground state to the p-like excited states are infrared active. A high-resolution Fourier transform spectrometer, and a liquid-helium cooled germanium bolometer and glass sample cryostat are ideally suited to study these effects. When silicon is exposed to neutron radiation, a fraction of the atoms are converted to phosphorus. After annealing, these impurity atoms occupy substitutional locations and are thus donors. When the initial crystal is p-type and the final phosphorus concentration is less than that of the acceptor, the sample is left p-type but highly compensated. This results in broadening of the transition lines. However, before complete annealing, it is discovered that a new, extremely shallow acceptor is formed, with an ionization energy of 28.24 meV, which is far shallower than any previously known. Neutral Be in Ge is known to be a double acceptor. Under uniaxial stress, the single hole $(1s)\sp2\ \to\ (1s)(np)$ excitation spectrum shows splittings and polarization effects. These piezospectroscopic effects were observed for a compressive force $\vec F\ \Vert$ (111) and $\vec F\ \Vert$ (100). The phenomenological shear deformation potential constants have been deduced for the ground and excited states of the D transition.

Degree

Ph.D.

Advisors

Ramdas, Purdue University.

Subject Area

Condensation

COinS