A study of infrared absorption due to intersubband transitions in p-type Si 1-x Ge x /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 the k·p and the tight-binding methods, with a strain Hamiltonian. Both of the Poisson and the Schrödinger equations are solved self-consistently to take into account a band-bending effect. The calculated quantum efficiency in a 40 Å Si 0.75 Ge 0.25 /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 μm 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.