FAR-INFRARED EMISSION AND ABSORPTION BY HOT CARRIERS IN SUPERLATTICES

Some of the earliest theoretical speculation, stimulated by the growth of semiconductor superlattices, focused on novel devices based on ver tical transport through engineered band structures; Esaki and Tsu prom ised Bloch oscillators in narrow mini-band systems and Kazarinov and S uris contemplated electrically stimulated intersubband transitions as sources of infrared radiation. Nearly twenty years later these materia l systems have been perfected, characterized and understood and experi ments are emerging that test some of these original concepts for novel submillimetre wave electronics. Here we describe recent experiments o n intersubband emission in quantum wells stimulated by resonant tunnel ling currents. A critical issue at this time is devising a way to achi eve population inversion. Other experiments explore 'saturation' effec ts in narrow miniband transport. Thermal saturation may be viewed as a precursor to Bloch oscillation if the same effects can be induced wit h an applied electric field.