Interface states in abrupt semiconductor heterojunctions

Abstract A perfect match of lattice constants is not normally possible in heterojunctions and, therefore, defects, mainly in the form of interfacial dislocations, are present at the heterojunctions interface. Experimental evidence for the electrical properties of isolated bulk dislocations, grain boundary dislocations and dangling bonds at surfaces, as well as at SiO 2 Si interfaces, suggests that interfacial defects at heterojunctions produce important effects. In particular, for lattice mismatches of about 1 per cent or greater, sufficient interface states should be created to bend the bands at the interface and, thus, largely determine the device characteristics. In addition, interfacial dislocations would be expected to cause severe minority carrier recombination, even for lattice mismatches of as low as 0·05 per cent. Therefore, efficient wide-gap-emitter action in Ge/GaAs p - n heterojunctions is likely to be difficult to achieve. The electrical characteristics of some n - n and p - p Ge/Si are reported and can be accounted for on the basis of a heterojunction theory including interface states. The electron affinity difference ( χ Ge - χ Si ) is 0·15 ± 0·03 eV as determined from the Ge/Si n - n structures.