TE- and TM-polarized roughness-assisted free-carrier absorption in quantumwells at midinfrared and terahertz wavelengths

A free-carrier absorption mechanism, in which a photon transition is accomp anied by an elastic interface-roughness scattering event, is considered for a few representative quantum well structures. Interface-roughness scatteri ng determines the low-temperature mobility in undoped narrow quantum wells such as those used in infrared lasers. It is found that in spite of the con tribution due to scattering to higher subbands, the absorption coefficient for TE-polarized light remains appreciably less than the semiclassical valu e at shorter wavelengths. The implications of these results for the recentl y proposed interband far-infrared and terahertz lasers based on "W" antimon ide structures are discussed. In the case of roughness-assisted absorption of TM-polarized light, transitions forbidden by symmetry and exclusion argu ments become allowed. However, the largest second-order contribution relati ve to first-order intersubband absorption tends to occur at wavelengths whe re the total absorption coefficient is rather small. [S0163-1829(99)10143-7 ].