PHYSICAL PROPERTIES OF SOLID SOLUTIONS OF CADMIUM PHOSPHIDE AND ZINC PHOSPHIDE.

摘要

A knowledge of the physical properties of solid solutions formed by two isostructural, direct bandgap semiconductors would be of great value in identifying potentially useful optical and electronic applications. Therefore, to investigate these properties and new thin film solar cell materials, a study of solid solutions of cadmium phosphide (Cd(,3)P(,2)) and zinc phosphide (Zn(,3)P(,2)) was conducted.;In the experimental structural, optical and electronic properties of single crystals of (Zn(,x)Cd(,1-x))(,3)P(,2), over the range 0 (LESSTHEQ) x (LESSTHEQ) 1, were investigated. Mechanical cutting and polishing, chemical polishing and thinning were used to prepare the optical samples. Metal electroplating and vacuum deposition of contacts were needed to prepare for the electronic transport measurements.;This investigation led to the following results and conclusions: (1) It is possible to fabricate sufficiently large single crystals of (Zn(,x)Cd(,1-x))(,3)P(,2) over the range 0 (LESSTHEQ) x (LESSTHEQ) 1. (2) Optical determinations of the absorption coefficient vs. wavelength showed that homogeneous samples maintained their direct bandgap quality. (3) Lattice constants vary roughly according to Vegard's Law between the endpoint compositions, confirming prior findings (A-85). (4) Conductivity type changes from n to p near and above 45 mole percent Cd(,3)P(,2). (5) A monotonic decrease of energy gap occurred with increasing concentration of Cd(,3)P(,2) as anticipated. (6) Transport property variations with temperature indicate that the p-type conductivity is due to interstitial phosphorus, while the n-type conductivity is due to interstitial cadmium. These results are more complete and vary from those in the open literature (A-85) probably due to different growth conditions. (7) Suitable p-n junctions for high conversion efficiency terrestial solar cells can be fabricated using a solid solution composition (Zn(,.5)Cd(,.5))(,3)P(,2) (Eg (TURN) 1ev) in conjunction with Zn(,3)P(,2) (Eg (TURN) 1.5ev).;After consideration of previous studies on these and similar materials, and Zn(,3)P(,2) as a photovoltaic material, an open capsule method of single crystal preparation was adopted.