A study of infrared absorption due to intersubband transitions inp‐type Si1−xGex/Si quantum wells has been performed. The influence of the hole envelope wave‐function and the subband structure on the absorption characteristics is evaluated. In the calculation, the subbands in a SiGe strained layer are computed by using a bond orbital model, which combines thek⋅pand the tight‐binding methods, with a strain Hamiltonian. Both of the Poisson and the Schro¨dinger equations are solved self‐consistently to take into account a band‐bending effect. The calculated quantum efficiency in a 40 A˚ Si0.75Ge0.25/Si quantum well detector is compared favorably with an experimental result. The structural dependence of infrared absorption on quantum well width, doping and Ge content in a wavelength range of 3–15 &mgr;m is investigated. By varying a well width, our study reveals that a maximum absorption coefficient is obtained when the energy level of the excited‐state subband is near the top of a quantum well. ©1995 American Institute of Physics.