SI SI1-XGEX MULTIQUANTUM WELLS - A ROUTE TO INFRARED DETECTORS/

Quantum-well detectors use intersubband transitions for the detection of long-wavelength infrared radiation. Such quantum-well structures pr ovide the electronic and optical properties for a new generation of in frared quantum detectors. II is shown that apart from GaAs/GaAlAs mult iquantum-well structures, which were studied extensively recently with respect to their potential application for infrared detection, Si/SiG e structures are suitable for this purpose as well. We have performed a systematic experimental study of intersubband transitions in modulat ion-doped p-type molecular beam epitaxy grown Si/SiGe quantum wells fo r well widths between 26 Angstrom and 65 Angstrom and Ge contents in t he range from 19% to 50%. Intersubband absorption occurs between 480 c m(-1) and 1830 cm(-1) for such structures. The widths of the absorptio n lines are only 20 meV as long as the excited states are confined wit hin the SiGe wells. When the excited states lie already in the continu um, a broadband photoresponse can be achieved. For this purpose Si/SiG e structures with sufficiently narrow SiGe wells (about 30 Angstrom) d oped to a level of p = 4 x 10(18) cm(-3) were used. Such structures ca n be directly grown on Si (001) substrates and are highly compatible w ith modem Si device fabrication technology which offers a tremendous a dvantage for the realisation of large scale two-dimensional infrared d etector arrays.