Theoretical and experimental studies of optical absorption in strained quantum-well structures for optical modulators

Theoretical and experimental results on excitonic and band-to-band absorption spectra in strained multiple-quantum-well structures are presented and discussed. The study is particularly motivated by the need to enhance optical absorption in devices such as optical modulators and high-speed photodiodes. We show that it is possible to merge the heavy- and light-hole excitonic resonances through use of biaxial tensile strain in the well regions. Calculations and experiments show a strong increase in optical absorption, by almost a factor of 2, due to this merger. The calculations include the heavy-hole--light-hole coupling which is essential to understand this phenomenon. The electric field dependence of optical absorption in strained quantum wells is also presented.