Intersubband absorption in Sb δ-doped Si/Si_1-xGe _x quantum well structures grown on Si (110)

Strong electron intersubband infrared absorption is observed for Sb δ-doped Si/Si_1-xGe_x multiple quantum well structures grown on (110) Si substrates. The intersubband absorption is shown to be allowed for both the optical field components perpendicular and parallel to the quantum wells due to the tilted ellipsoidal of constant energy surfaces. About 90% infrared absorption is measured by a Fourier transform infrared spectrometer using a waveguide structure with 10 internal reflections. For various samples used in experiments, absorption peaks ranging from 4.9 to 5.8 μm are observed. The peak energy is shown to be tunable by changing the Ge composition in the Si_1-xGe_x barriers and the doping concentration in the Si quantum wells.