OBSERVATION OF ELECTROLUMINESCENCE FROM PSEUDOMORPHIC SI1-XGEX ALLOY LAYERS

The electroluminescence (EL) and photoluminescence (PL) of ultrametastable Si1-xGex layers grown by molecular beam epitaxy (MBE) on Si(100) substrates has been studied. Two layers 150 and 175 nm thick (samples B2005 and C0997 respectively) were pseudomorphically grown on silicon in two different MBE chambers at 450-degrees-C with x almost-equal-to 0.25 and x almost-equal-to 0.23 respectively. At liquid-helium temperature both samples show luminescence spectra from the Si1-xGex layers consisting of resolved band edge recombination and a broad low energy band peaking at about 810 meV. In one sample (B2005) the broad band is dominant; in the other sample (C0997) the band edge PL and EL signals are dominant. Variation of the exciting current density or laser power over a wide range shows a different power dependence for the low energy band, the Si1-xGex band edge luminescence and the silicon substrate luminescence. In addition, we have studied the EL of fully strained Si1-xGex single quantum wells. At constant excitation current density the EL signal increases with decreasing layer thickness, while the peak energy shifts to higher energy owing to the quantum size effect. For thin quantum wells, two lines at 969 and 897 meV are observed, known as the G line and the E line respectively, which are associated with a C(s)-Si(i)-C(s) defect.