n-n Semiconductor heterojunctions

Junctions between n-type semiconductors of different electron affinity show rectification if the junction is sufficiently abrupt. Such structures are potentially very fast, because only majority-carrier transport is involved. InPGaAs n-n junctions were fabricated with an epitaxial vapor-growth method. Typical V-I characteristics display a forward-voltage drop of 0·3 V at 10 Acm2, and a reverse leakage current of 0·5 Acm2 at −2 V. No storage was observable in switching measurements on these devices. Other observations demonstrate that these junctions are indeed n-n heterojunction rectifiers. Ideal semiconductor-semiconductor contacts are reviewed and the concepts extended to graded contacts. An abruptness requirement for rectification to exist is developed on the basis of this ideal model for the effects of junction grading during fabrication. If D is the diffusion constant of the fastest moving lattice atom at the growth temperature, t the growth time, δχ the total electron affinity change through the junction, and LD the Debye length on the low-electron affinity side, then for appreciable rectification to exist a condition which must be satisfied is Dt