Researchers Vie to Achieve a Quantum‐Dot Laser

If semiconductor quantum‐well lasers are so successful, shouldn't quantum‐wire or quantum‐dot lasers be even better? That's a question that many researchers have set out to answer. Quantum wells confine the charge carriers in one dimension; wires confine them in two; and dots, in three. (Quantum dots are clusters of semiconductor material with a few thousand atoms.) As a result of their confinement, the charge carriers occupy discrete energy levels similar to those of electrons in an atom. Energy pumped into the system raises the charge carriers from one energy level to the next; none of it goes to random motion, because there are no other degrees of freedom. Thus, one expects any lasing from the dots to occur with high efficiency and at lower threshold current than in either quantum wells or quantum wires.