ELECTRICAL AND OPTICAL BANDGAPS OF GEXSI1-X STRAINED LAYERS

Theoretical and experimental evidence is presented to show that the ef fective mass of holes is reduced due to strain in the GexSil-x layers grown on Si(100) substrate. In this paper, it is shown theoretically t hat due to this change in the hole effective mass, the reduction of ba ndgap of a heavily doped (i.e., more than similar to 1 X 10(18) cm(-3) ) GexSil-x strained layer base determined by measuring the collector c urrent of the heterostructure bipolar transistor is smaller than the b andgap reduction obtained from optical measurements. When uncertaintie s in the value of the mass and in the experimental results are taken i nto account, agreement between the theoretical and experimental bandga p reduction values is satisfactory. A significant result obtained in t he paper is that a high Ge and doping concentrations in the base suppr ess the collector current and make it smaller than the value that woul d be obtained if heavy doping effects are neglected.