The Double-Heterostructure Concept in Lasers, LED's, and Solar Cells

The double hetero-structure concept of Kroemer, Alferov & Kazarinov (1963), solved the basic problem in solid-state electronics, namely, how to keep carriers away from surfaces, which invariably have defects and dangling bonds. The facility of alloying different III-V semiconductors with different bandgaps, made it possible to safely confine both electrons and holes within their own potential wells. As a side-benefit, the small refractive index contrast provides optical wave-guiding for semiconductor lasers, which emerged as the dominant form of laser in the late 20 th century. Since electrons and holes are NOT lost at the surfaces, they become available for light emission in Light Emitting Diodes, or for direct extraction from Solar Cells. The double heterostructure is essential for all these devices. Indeed, it took many decades to recognize that the double heterostructure makes the best Solar Cells.