Absorption and emission spectroscopy of intersubband transitions in Si1−xGex/Si quantum wells

Abstract

An experimental study of the infrared properties of pseudomorphically grown Si1−xGex quantum wells is presented. Undoped quantum wells grown by ultrahigh vacuum chemical vapor deposition are investigated by photoinduced absorption and emission spectroscopies. The 2 nm thick Si0.7Ge0.3 quantum wells exhibit infrared absorption around 10 μm wavelength which is associated with bound-to-continuum intersubband transitions. We show that the study of photoinduced intersubband absorption gives valuable information on the dynamics of photocarriers. An average lifetime τ≈2.5 μs is deduced from the frequency dependence of the photoinduced infrared absorption. We show that the temperature dependence of the photoinduced absorption is governed by the thermal excitation of the carriers above the barriers. The infrared emission of the quantum wells is studied in a second part. In III–V quantum wells, intersubband transitions around 10 μm wavelength are clearly evidenced by room temperature infrared emission spectroscopy. In the case of Si-SiGe quantum wells, only blackbody and defect-related emissions have been observed in the mid-infrared spectral range. The vanishing room-temperature emission is correlated with the weak photoinduced room-temperature absorption.