Correlation Between Band 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 magneto-resistance. Our sample, grown by MBE, had a period d=d ₁+d ₂ (124 layers) of $d_{1}=8.6~\mathrm{nm}~\mathrm{(HgTe)} /d_{2}=3.2~\mathrm{nm}~\mathrm{(CdTe)}$. Calculations of the spectras of energy E(d ₂), E(k _z ) and E(k _p ), respectively, in the direction of growth and in plane of the superlattice; were performed in the envelope function formalism. The energy E(d ₂,Γ,4.2 K), shown that when d ₂ increase the gap E _g 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 $2.5 \times 10^{5}~\mathrm{cm}^{2}/ \mathrm{V\,s}$. This allowed us to observe the Shubnikov-de Haas effect with n=3.20×10¹² cm⁻². Using the calculated effective mass ($m^{*}_{E1}(E_{F}) = 0.05 m_{0}$) of the degenerated electrons gas, the Fermi energy (2D) was E _F =88 meV in agreement with 91 meV of thermoelectric power α. In intrinsic regime, α∼T ^−3/2 and R _H T ^3/2 indicates a gap E _g =E ₁−HH ₁=101 meV in agreement with calculated E _g (Γ,300 K)=105 meV. The formalism used here predicts that the system is semiconductor for d ₁/d ₂=2.69 and d ₂<100 nm. Here, d ₂=3.2 nm and E _g (Γ,4.2 K)=48 meV so this sample is a two-dimensional modulated nano-semiconductor and far-infrared detector (12 μm<λ _c <28 μm).