TRAPEZOIDAL DELTA-DOPED SUPERLATTICE FOR FAR-INFRARED DETECTION

A new superlattice is proposed that is based on non-degenerate single- crystal conventional semiconductors of InSb, InAs, GaAs, and Ge type. The superlattice consists of alternating pairs of delta-doped ultra-th in layers of p and n type. The distance between the identical layers o f p (or n) type, that constitute a pair, is chosen in such a way that the energy spectrum of holes (or electrons) in quasi-continuous. The d istance between two adjacent pairs of layers of p and n type is suffic iently small, so that an extra-large built-in electric field may be ge nerated in the regions between the pairs. In such a superlattice, pote ntial has a trapezoidal shape and can be viewed as a periodic set of a lternating non-quantized wells for electrons and holes that are separa ted by very thin regions of extra-large field. We found that the light absorption in the regions of extra-large field is significant up to 3 mu m for the GaAs superlattice and up to 4.5 mu m for the Ge superlat tice. For the InSb and InAs superstructures, the interband absorption coefficient is close to its fundamental-band edge value and slightly d epends on the wavelength up to 50 to 100 mu m In contrast to the quant um-well superlattices, the proposed superstructure a) does not have he terojunctions and b) absorbs IR radiation of any polarization in a ver y wide spectral region. Effective spatial separation of photo-generate d carriers ensures their lifetimes to be gigantic thus achieving a hig h level of photo-response.