Acousto-optic modulation of III-V semiconductor multiple quantum wells

Abstract

We present an analysis of the effect of surface acoustic waves ͑SAW's͒ on the optical properties of III-V semiconductor multiple quantum wells ͑MQW's͒. Modulation spectra at the fundamental and second harmonic of the SAW frequency are presented. The SAW modulates the optical properties of the MQW primarily by changing optical transition energies. The SAW generates both strains, which modulate the transition energies by deformation potential effects, and electric fields, which modulate the transition energies by the quantum confined Stark effect. We find that modulation of the transition energies by strain effects is usually more important than by electric-field effects. If large static electric fields occur in the MQW, the SAW-generated electric field can mix with the static field to give optical modulation, which is comparable in magnitude to modulation from the deformation potential effect. If there are no large static electric fields, modulation by the SAW-generated fields is negligible. A large static electric field distributes oscillator strength among the various optical transitions so that no single transition is as strong as the primary allowed transitions without a static electric field. To achieve the maximum modulation for fixed SAW parameters, it is best to modulate a strong optical transition. Thus optimum modulation occurs when there are no large static electric fields present and that modulation is primarily from deformation potential effects. We specifically consider Ga x In 1Ϫx As/Ga x Al 1Ϫx As MQW's grown on ͑100͒ and ͑111͒ oriented substrates, but our general conclusions apply to other type I MQW's fabricated from III-V semiconductors.

Modulation of photonic structures by surface acoustic waves

“…Several groups have proposed the energetic band-gap shifts due to the quantum-confined Stark effect as a mechanism for light modulation by acoustic waves in semiconductor quantum well structures [145][146][147][148]. We note, however, that the strain-induced shifts of the excitonic levels reach several millielectronvolts (cf figure 24(b)) and are comparable to even higher than the ones due to the quantum-confined Stark effect induced by the surface acoustic wave piezoelectric field [147]. The photonic resonances have several advantages for light modulation when compared with the electronic ones.…”

First- and second-order piezoelectricity in III-V semiconductors

“…Conclusions drawn from bulk measurements, on the other hand, are usually shadowed by the appearance of free carriers (residual, intrinsic, or photoinduced) effectively screening the field. In the case of III-V zinc-blende heterostructures specifically, the intrinsic strain-induced electric fields are held responsible for strong effects on the transport properties, 21 optical characteristics, [22][23][24] and acousto-optical modulation 25 in a way which may lead to the microstructural engineering of novel optical and electronic devices. 26,27 The interest on these modified properties is therefore manyfold: the understanding of the physics involved and the development of new applications, that is, integrated, mixed-effect devices, optical switches, modulators, and nonlinear devices.…”