ELECTRON MOBILITIES AND QUANTUM HALL-EFFECT IN MODULATION-DOPED HGTE-CDTE SUPERLATTICES

Photoassisted molecular-beam epitaxy and controlled modulation doping have been used to grow HgTe-CdTe superlattices with n-type carrier concentrations of up to 3 x 10(17) cm-3. It is found that in contrast to Hg1-xCdxTe alloys where the electron mobility decreases strongly with donor concentration, mu-n in the modulation-doped superlattices is nearly independent of N(D) at large N(D). We also discuss an observation of the quantum Hall effect associated with carriers distributed throughout the interior of a HgTe-CdTe superlattice. Whereas previous reports of quantized steps in the Hall conductivity have involved a small number of conduction channels (hence a small fraction of the superlattice periods), we observe plateaus at multiples of almost-equal-to 200e2/h in a number of 200-period superlattices with high doping levels. This indicates participation by nearly all wells in the superlattice, and implies that the controlled doping is extremely uniform.