ABSORPTION AND EMISSION-SPECTROSCOPY OF INTERSUBBAND TRANSITIONS IN SI1-XGEX SI QUANTUM-WELLS/

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 pho toinduced absorption and emission spectroscopies. The 2 nm thick Si0.7 Ge0.3 quantum wells exhibit infrared absorption around 10 mu m wavelen gth which is associated with bound-to-continuum intersubband transitio ns. We show that the study of photoinduced intersubband absorption giv es valuable information on the dynamics of photocarriers. An average l ifetime tau approximate to 2.5 mu s is deduced from the frequency depe ndence of the photoinduced infrared absorption. We show that the tempe rature dependence of the photoinduced absorption is governed by the th ermal excitation of the carriers above the barriers. The infrared emis sion of the quantum wells is studied in a second part. In III-V quantu m wells, intersubband transitions around 10 mu m wavelength are clearl y evidenced by room temperature infrared emission spectroscopy. In the case of Si-SiGe quantum wells, only blackbody and defect-related emis sions have been observed in the mid-infrared spectral range. The vanis hing room-temperature emission is correlated with the weak photoinduce d room-temperature absorption. (C) 1998 American Vacuum Society.