QUASI-ELASTIC RAMAN-SCATTERING IN N-TYPE GAAS

The quasielastic part of the Raman spectrum in the spectral range <(nu )over tilde> < 100 cm(-1) offers the possibility of detecting the free electron concentration of semiconductors down to about 5 x 10(14) cm( -3) A series of n-type GaAs samples was investigated using NIR Raman s pectroscopy (lambda(ex) = 1064 nm), and an analytical method to obtain the carrier concentrations from the spectra is proposed. The sources of error and the limits of the method are discussed by comparison with the corresponding Hall measurements. Within the range 1 x 10(15) cm(- 3) < n < 1 x 10(17) cm(-3) the accuracy of the obtained free electron concentrations is estimated to be about 25%. The detection limit of th e quasielastic Raman spectroscopy is nearly two orders of magnitude be tter than the determination of n from the coupled LO-phonon-plasmon mo des.