Semiconductor lasers: from homojunctions to quantum dots

A brief review of the development of physics and technology of semiconductor lasers, beginning from theoretical proposals made in the late 1950s up to now, is presented. For example, the threshold current density at room temperature, which was 10⁵ – 10⁶ A cm^-2 in 1963, has been now reduced to ~10 A cm^-2. The main factors that have provided this progress are considered. The mechanisms of energy conversion determining the high efficiency of semiconductor lasers are discussed in detail.