Abstract
The large majority of solid state lamps currently available take advantage of the phenomenon of electroluminescent recombination at forward biased p–n junctions (homojunctions) in III–V compound semiconductors or related derivatives (GaP, GaAsP, etc.). The range of colours, sizes and luminous efficiencies likely to become available are subject, however, to certain fundamental limitations of the materials used. These are related to the size and nature of the forbidden energy gap, crystal defect structure as well as other factors. Applications will also be limited by the range of promising non-semiconductor display systems in advanced stages of development against which large LED arrays will not be able to compete.Restricting these applications to the more viable small alphanumerics and indicator lamps, however, alternative semiconductor materials with extremely attractive physical properties exist, although other problems take the place of those mentioned above. For example, most of the II–VI compound semiconductors (CdS, ZnSe, etc.) cannot be doped both n and p type, precluding the manufacture of p–n diode lamps.In this paper the desirable properties of materials to be developed for future lamp applications are briefly discussed, against background data on current materials, semiconductor materials fulfilling these criteria are introduced and ways in which existing technological difficulties may be circumvented are described.The paper is concluded with comments upon arguably the most interesting development of recent years, the interfacing of silicon with low voltage excitable “phosphors” in the form of oriented epitaxial semiconductor films. Preparation, properties and advantages in direct integration with SIC addressing machinery are outlined.