Photoelectronic study of GaAs epilayers and InxGa1-xAs/GaAs quantum wells.

The photoelectromagnetic (PEM) effect was used to perform experiments on photocarriers' transport properties in GaAs substrates and epitaxial layers. For the undoped semi-insulating substrate, the carriers' mobility $\mu$ at T = 77K was measured by PEM effect method, giving a value of $\mu$ = 40,000 cm$\sp2$ V$\sp{-1}$s$\sp{-1}$. It was found that the carriers' diffusion length is L$\sb{\rm D}$ = 0.27 $\mu$m at T = 300K and L$\sb{\rm D}$ = 0.44 $\mu$m at T = 77K. For the 3.4$\mu$m thick epitaxial layer grown by metal-organic chemical vapour deposition (MOCVD), the carriers' diffusion length was measured to be L$\sb{\rm D}$ = 2.6 $\mu$m at T = 300K, L$\sb{\rm D}$ = 3.1 $\mu$m at T = 77K and L$\sb D \approx$ 3.5 $\mu$m at T = 5K. A photocurrent (PC) spectroscopy study of In$\sb{\rm x}$Ga$\sb{\rm 1-x}$As/GaAs quantum wells on Cr-doped and undoped substrates has been performed. Several well-resolved structures related to inter-subband transitions are observed in the photoconductivity spectra for both T = 300K and T = 77K, and they are in good agreement with calculation taking into account the strain-induced splitting of the bands. Both Cr-doped and undoped substrates have been found to influence the results, as shown by optical quenching techniques