INTERSUBBAND ABSORPTION IN SB DELTA-DOPED SI/SI1-XGEX QUANTUM-WELL STRUCTURES GROWN ON SI (110)

Strong electron intersubband infrared absorption is observed for Sb delta-doped Si/Si1-xGex 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-mu-m are observed. The peak energy is shown to be tunable by changing the Ge composition in the Si1-xGex barriers and the doping concentration in the Si quantum wells.