Wave function engineering for normal incidence intersubband infrared detection

We propose a new intersubband infrared photodetector concept, the island in sertion infrared detector ((ID)-D-3), with the aim of achieving improved no rmal incidence absorption characteristics over the quantum well infrared ph oto-detector (QWIP). The lack of normal incidence absorption in typical QWI P structures is the direct consequence of the in-plane translational symmet ry of the quantum well. The active region of our proposed detector structur e consists of a quantum well as in QWIPs, but inserted with submonolayers ( SMLs) of a lattice mismatched semiconductor. The insertion of SMLs should n ot disrupt epitaxial growth, while the presence of strain would promote the formation of embedded islands. The embedded islands introduce lateral (in- plane) variations in the quantum well wave function, which in turn enhance inter-conduction-subband absorption of normal incidence radiation. Specific implementations include the insertion of SMLs of InAs, InSb, GaSb, AlSb, o r AlAs in GaAs quantum wells. Results of preliminary model calculations sho w that InAs island insertions can indeed induce substantial lateral variati ons in GaAs quantum well wave functions, provided that the island sizes are comparable to or larger than the electron deBroglie wavelength. Our result s also suggest that optimization of normal incidence absorption would likel y require the use of multiple SML insertions at different positions along t he quantum well. These promising initial results suggest that the island in sertion infrared detector concept merits further theoretical and experiment al investigations. (C) 2001 Elsevier Science B.V. All rights reserved.