Valence band engineering in strained-layer structures

Abstract

It is now possible to grow high-quality strained-layer superlattices, in which individual layers are composed of semiconductor materials which would normally have significantly different lattice constants. Strained structures open new possibilities for band-structure engineering and applications, but place even higher demands on crystal growth techniques.In this Review, we first describe some of the growth that has been achieved and the theoretical and experimental limits on good quality growth. We then discuss in detail the electronic structure of strained quantum wells, and in particular the possibility of valence band engineering in strained layers. Axial strain splits the degeneracy of the light-and heavy-hole zone centre states, accessing a range of subband structures, including the possibility of the highest band being light-hole-like, and of holes with electron-like zone centre masses. We next describe the experimental evidence confirming such subband structures.This strain-based band engineering suggests new device applications, including high hole mobility transistors and low threshold current, longwavelength lasers. We review what has been achieved in respect of the main proposed device applications to date. Strained layers are also of interest for the new materials combinations which they allow. We briefly overview some of the materials-based advantages, and conclude that strained layers will continue to attract significant attention.

Self-assembled (In,Ga)As/GaAs quantum-dot nanostructures: strain distribution and electronic structure

“…The effects of strain on semiconductors have therefore motivated a significant interest in calculating its magnitudes in a broad range of devices. 3 The hydrostatic (e h ) component of strain, for example, usually shifts the conduction and valence band-edges of semiconductors; biaxial (s b ) strain, on the other hand, modifies the valence bands by splitting the degeneracy of the light-and heavy-hole bands. These effects have a profound impact on the electronic and optical properties of the structures out of which devices might be fabricated.…”

Coupling of ultrathin InAs layers as a tool for band-offset determination

“…This is, on the one hand, due to their potential application in optoelectronic devices. 1,2 On the other hand, since InAs and GaAs have one of the largest lattice mismatches among III-V semiconductors, ultrathin InAs/GaAs quantum wells serve as a model system to study the electronic structure and optical properties in an almost ideal twodimensional but highly compressively strained material system. In particular, the band alignment, the magnitude of the band offsets, and the degree of confinement are recent topics of intense debate.…”

Ultrafast Processes in Semiconductor Structures

“…In response to the biaxial tension, the GaAs1-x Pl ayer relaxes along the growth direction, giving rise to an uniaxial compression. The total strain reduces the energy gap and shifts the heavy hole and light hole valence subbands to higher energies [37]. The amount of band-edge shift of the lh subband is larger than that of the hh one.…”