PHOTOVOLTAGE AND PHOTOCURRENT SPECTROSCOPY OF P+-I-N+ GAAS/ALGAAS QUANTUM-WELL HETEROSTRUCTURES

The photoelectric properties of p+-i-n+ heterostructures that contain a GaAs/AlGaAs superlattice, grown by molecular beam epitaxy, have been investigated. The nominally undoped multi-quantum-well region was excited by photons whose energies were varied within the spectral region of valence-to-conduction subband transitions. The dark- and light-induced perpendicular transport was examined. The intense spectral features observed by photovoltage (PV) and photocurrent (PC) measurements were ascribed to excitonic transitions between the heavy and light hole electron states; their energetic location and line shape (half width at half peak and integrated area) were carefully studied in the temperature interval 10-300 K. The excitonic nature of the spectral peaks showing a conspicuous red shift under a reverse bias (Stark shift) were confirmed by electroreflectance measurements. The full analogy and the origin of the two (PV and PC) photoresponse signals are clearly proved. The spectral features can be explained by the absorption properties of the quantum wells, while the variation of the peak integrated area as a function of the temperature is dominated by the particular transport mechanism. The integrated area of the peaks shows a minimum at about 100 K which seems to be due to the occurrence of two different tunneling mechanisms.