ELECTRIC-FIELD DEPENDENT PHOTOCURRENT AND ELECTROREFLECTANCE SPECTRA OF INGAAS/ALGAAS MULTIPLE STRAINED QUANTUM-WELL STRUCTURES

We present results on excitonic transitions and confinement at high electric fields from photocurrent and electroreflectance spectra of an In 0.17Ga0.83As/Al0.3Ga0.7As strained quantum well structure fabricated into a Schottky barrier diode. Up to the highest field attained, 1.7×105 V/cm, we observe a well-defined exciton line at the band edge (in contrast to data on similar GaAs/Al 0.3Ga0.7As structures), a feature important for potential optoelectronic applications. At low fields, "allowed" (Δn=0) transitions dominate the photocurrent spectra, but with increasing field "forbidden" transitions (allowed because of reduced symmetry and valence-band mixing) grow in intensity and eventually dominate the above-gap response. In the electroreflectance spectra, the forbidden transitions are relatively strong, even at low field. The allowed above-gap transitions nearly vanish at low temperature because of the small field dependence of the higher lying quantum well energy levels.