ANM 2010

ANM 2010
3^rd International Conference on Advanced Nano Materials
12-15 September 2010 - Agadir, Morocco

Abstract

	ANMM335
	BAND STRUCTURE AND MAGNETO- TRANSPORT PROPERTIES IN II-VI NANOSTRUCTURES SEMICONDUCTORS. APPLICATION TO INFRARED DETECTOR SUPERLATTICES
	Abdelhakim Nafidi
	Group of Condensed Matter Physics, Physics Department, Faculty of Sciences, B.P 8106 Hay Dakhla, University Ibn Zohr, 80000 Agadir, Morocco
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	HgTe is a zero gap semiconductor when it is sandwiched between the wide gap semiconductor CdTe layers yield to a small gap HgTe/CdTe superlattice witch is the key of an infrared detector. Our two samples denoted SL1 and SL2, grown by molecular beam epitaxy (MBE) on a CdTe (111) substrate at 180 °C, had a period d=d1+d2 (90 layers) of HgTe(d1=5,6 nm) / CdTe(d2 =3 nm) and (100 layers) of HgTe(d1=18 nm) / CdTe (d2=4.4 nm). Our calculations of the specters 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. In the SL1, X-ray diffraction, conductivity, Hall effect, Seebek and Shubnikov-de Haas effects and angular dependence of the transverse magnetoresistance were measured. The profile of the (222) Bragg reflection indicated a modulated structure. At 4.2 K, the sample exhibits p type conductivity with a Hall mobility of 8200 cm2/Vs. This allowed us to observe the Shubnikov-de Haas effect with p = 1,80 10¹² cm^-2. Using the calculated effective mass (m*_HH = 0,297 m₀) of the degenerated heavy holes gas, the Fermi energy (2D) was EF=14 meV in agreement with 12 meV of thermoelectric power α. In intrinsic regime, α~T^-3/2 and R_H T^3/2 indicates a gap Eg =E₁-HH₁= 190 meV in agreement with calculated Eg(Γ, 300 K) =178 meV. The formalism used here predicts that the system is semiconductor for d1/d2 = 1,87 and d2 < 140 Å. Here, d2=30 Å and Eg (Γ,4.2 K) = 111 meV so this sample is a two-dimensional modulated nanostructure medium-infrared detector semiconductor (7µm<λ<11µm). This superlattice is a stable alternative for application in medium infrared optoelectronic devices than the random alloys Hg_0.8Cd_0.2Te because the small composition x=0.22, with Eg (Γ, 300 K) =183 meV, is difficult to obtain while growing the ternary alloys and the transverse effective masse in superlattice is two orders higher than in the alloy. So the tunnel length is small in the superlattice. In the SL2, the angular dependence of the transverse magnetoresistance follows the two-dimensional (2D) behaviour with Shubnikov-de Haas oscillations. While, the hall voltage goes to zero when the field is parallel to the plane. At low temperature, the sample exhibits p type conductivity with a hole mobility of 900 cm²/V.s. A reversal the sign of the weak-field Hall coefficient occurs at 25 K with an electron mobility of 3.104 cm²/Vs. In intrinsic regime, the measured Eg ≈ 38 meV agree with calculated Eg(Γ,300K)=34 meV witch coincide with the Fermi level energy. The formalism used here predicts that the system is semi metallic when the ratio d1/d2 is greater than 4. In our case, d1/d2 =4.1 and the gap Eg(Γ,4.2K) =3 meV. In spite of it, this sample exhibits a semi metallic p type conduction mechanism, with a quasi-two-dimensional behavior and is a far-infrared detector (50 µm<λ< 450 µm). The investigated thicknesses of the SL2 sample situate it at the semiconductor to semimetal electronic transition. In conclusion, the HgTe/CdTe nano-superlattice is a stable alternative for application in infrared optoelectronic devices than the alloys Hg_1-xCd_xTe.