Far-infrared magnetooptical generalized ellipsometry determination of free-carrier parameters in semiconductor thin film
- PDF / 154,868 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 62 Downloads / 220 Views
M5.32.1
Far-infrared magnetooptical generalized ellipsometry determination of free-carrier parameters in semiconductor thin film structures Tino Hofmann, Marius Grundmann, Solid State Physics and Acoustics Group, Faculty of Physics and Geosciences, University of Leipzig, GERMANY; Craig M. Herzinger, J.A.Woollam Co., Lincoln, NE, USA; Mathias Schubert, Wolfgang Grill, Solid State Physics and Acoustics Group, Faculty of Physics and Geosciences, University of Leipzig, GERMANY;
ABSTRACT In accord with the Drude model, the free-carrier contribution to the dielectric function at infrared wavelengths is proportional to the ratio of the free-carrier concentration N and the effective mass m*, and the product of the optical mobility µ and m*. Typical infrared optical experiments are therefore sensitive to the free-carrier mass, but determination of m* from the measured dielectric function requires an independent experiment, such as an electrical Halleffect measurement, which provides either N or µ. Highly-doped zincblende III-Vsemiconductors exposed to a strong external magnetic field exhibit non-symmetric magnetooptical birefringence, which is inversely proportional to m*. If the spectral dependence of the magnetooptical dielectric function tensor is known, the parameters N, m* and µ can be determined independently from optical measurements alone. Generalized ellipsometry measures three complex-valued ratios of normalized Jones matrix elements, from which the individual tensor elements of the dielectric function of arbitrarily anisotropic materials in layered samples can be reconstructed. We present the application of generalized ellipsometry to semiconductor layer structures at far-infrared wavelengths, and determine the magnetooptical dielectric function for n-GaAs and n-AlGaInP for wavelengths from 100 µm to 15 µm. We obtain the effective electron mass and mobility results of GaAs in excellent agreement with results obtained from Hall-effect and Shubnikov-de-Haas experiments. The effective electron mass in disordered nAlGaInP obtained here is in very good agreement with previous k⋅p calculations. (Far)-infrared magnetooptic generalized ellipsometry may open up new avenues for non-destructive characterization of free-carrier properties in complex semiconductor heterostructures.
INTRODUCTION The accurate optical measurement of the “inertial” effective mass m* of free-charge carriers has been a long term goal.1 The square of the free-charge-carrier (unscreened) plasma frequency ω∗p2 and broadening γp can be derived from the dielectric function ε.2 Under simplified assumptions about the free-carrier momentum distribution function - a single-species carrier plasma taken as example - ω∗p2 and γp translate into the coupled quantities N/m* and m*µ.3 For determination of the effective mass m* and the free-carrier mobility µ, the free-carrier concentration N must be known from a different experiment. Usually, the electrical Hall effect is measured to access N, which requires ohmic contacts to the sample. No distinction can be ma
Data Loading...
