Effect of inhomogeneity on quantum well far-infrared lasers

The effect of inhomogeneity on quantum well far-infrared lasers caused by quantum well thickness and composition fluctuations is discussed. Assuming a linear distribution corresponding to systematic shift and a Gaussian distribution corresponding to random deviation and for a modest deviation sigma=+/-3.4 meV (approximately equivalent to a 1 monolayer fluctuation), we have found that the gain is reduced by 20% and 37% and the gain full half width is broadened by 46% and 85%, respectively. Because the broadening mechanism is inhomogeneous and it is much wider than the cavity mode separation, this will lead to multi-mode operation unless selection is provided. It also indicates that if the structural inhomogeneity is small enough the broadening is dominated by the Lorentzian broadening and it is still possible to obtain single mode action due to mode competition. The calculation is based on a rectangular quantum well, but the conclusion is also applicable to all other semiconductor lasers based on multi-quantum well structures. (C) 1998 American Institute of Physics. [S0021-8979(98)06403-2].