Trapezoidal Delta-Doped Superlattice for Far-Infrared Detection

Abstract

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 δ-doped ultra-thin layers of p and n type. The distance between the identical layers of 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 distance between two adjacent pairs of layers of p and n type is sufficiently small, so that an extra-large built-in electric field may be generated in the regions between the pairs. In such a superlattice, potential has a trapezoidal shape and can be viewed as a periodic set of alternating non-quantized wells for electrons and holes that are separated 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 μm for the GaAs superlattice and up to 4.5 μm for the Ge superlattice. For the InSb and InAs superstructures, the interband absorption coefficient is close to its fundamental-band edge value and slightly depends on the wavelength up to 50 to 100 μm. In contrast to the quantum-well superlattices, the proposed superstructure a) does not have heterojunctions and b) absorbs IR radiation of any polarization in a very wide spectral region. Effective spatial separation of photo-generated carriers ensures their lifetimes to be gigantic thus achieving a high level of photo-response.