Characterization of p-N Si1-xGex/Si heterojunctions grown by limited reaction processing

p-n Si_1-xGe_x/Si heterojunction diodes were grown by limited reaction processing (LRP) and fabricated into device structures. Alloy layer thicknesses were varied from 60 to 350 nm with x=0.22. The forward current-voltage characteristics of diodes with Si_1-xGe_x layer thickness of 100 nm and below have ideality factors n, which are less than 1.01 from turn-on to a point where bulk resistance dominates. At a thickness of 110 nm, the low current ideality factor degradation becomes detectable. At 220 nm, n=1.24, and when the thickness reaches 350 nm, no clear ideal region even exists. An increase in recombination current with thickness is believed to be a result of the generation of electrically active defects in the vicinity of the heterointerface accompanying strain relaxation. Measurements of the diode saturation current vs. temperature reveal a strong dependence on the bandgap of the Si_1-x Ge_x layer