Correlation between ban structure and magneto-transport properties in HgTe/CdTe two-dimensional far-infrared detector superlattice

Abstract

Theoretical calculations of the electronic properties of n-type HgTe/CdTe superlattices (SLs) have provided an agreement with the experimental data on the magneto-transport behaviour. We have measured the conductivity, Hall mobility, Seebeck and Shubnikov-de Haas effects and angular dependence of the magnetoresistance. Our sample, grown by MBE, had a period d = d1 + d2 (124 layers) of d1 = 8.6 nm (HgTe)/d2 = 3.2 nm (CdTe). Calculations of the spectras of energy E(d2), E(kz) and E(kp), respectively, in the direction of growth and in plane of the superlattice; were performed in the envelope function formalism. The energy E(d2,Γ, 4.2 K), shown that when d2 increase the gap Eg decrease to zero at the transition semiconductor to semimetal conductivity behaviour and become negative accusing a semimetallic conduction. At 4.2 K, the sample exhibits n type conductivity, confirmed by Hall and Seebeck effects, with a Hall mobility of 2.5×105 cm2/V s. This allowed us to observe the Shubnikov-de Haas effect with n = 3.20×1012 cm−2. Using the calculated effective mass (m∗ E1(EF ) = 0.05m0) of the degenerated electrons gas, the Fermi energy (2D) was EF = 88 meV in agreement with 91 meV of thermoelectric power α. In intrinsic regime, α ∼ T −3/2 and RH T 3/2 indicates a gap Eg = E1−H H1 = 101 meV in agreement with calculated Eg(Γ, 300 K) = 105 meV. The formalism used here predicts that the system is semiconductor for d1/d2 = 2.69 and d2 < 100 nm. Here, d2 = 3.2 nm and Eg(Γ, 4.2 K) = 48 meV so this sample is a two-dimensional modulated nano-semiconductor and far-infrared detector (12 µm < λc < 28 µm).