THERMAL HOLE EMISSION FROM SI SI(1-X)GEX/SI QUANTUM-WELLS BY DEEP-LEVEL TRANSIENT SPECTROSCOPY/

We report on the determination of the valence band offset between stra ined Si1-xGex and unstrained Si layers by deep level transient spectro scopy (DLTS) on Si/Si1-xGex/Si quantum well (QW) structures. A problem of this technique is to store the holes long enough (>1 ms) in the QW so that the thermal emission of holes is the dominating process. We a chieved sufficiently long hole storage times by using two different st ructures. In the first ones, this is obtained by selective growth whic h leads to a lateral limitation of the smooth QW layer, and with good Schottky contacts. For the second ones, the localization of holes is d ue to the presence of Si1-xGex islands. For a sample containing a smoo th QW with X(Ge)=0.17 a valence band offset of 140+/-20 meV was obtain ed and for the island layer with X(Ge)=0.3 a value of 258+/-20 meV was found. These results are in good agreement with theory. The DLTS meas urements are compared to admittance spectroscopy results and photolumi nescence measurements. (C) 1995 American Institute of Physics.