Effect of interface quality on the electrical properties of p-Si/SiGe two-dimensional hole gas systems

Electrical properties have been examined for single Si/Si0.8Ge0.2 p-type modulation-doped heterostructures which have been grown by molecular beam epitaxy. It is shown that the two-dimensional hole gas in a normal modulation-doped heterostructure (doped layer on the surface side) has a higher mobility than in an inverted structure (doped layer on the substrate side). Secondary-ion mass spectrometry analysis indicates that the lower mobility in the inverted structure is due to surface segregation of boron. Hole mobilities as high as 6000 cm2/V s at 2 K and 3800 cm2/V s at 6 K have been obtained which are the highest values reported so far for Si/SiGe heterostructures.