Betko, J.

Fedor, J.

Hasenöhrl, S.

Morvic, M.

Novák, J.

Università del Salento: ESE - Salento University Publishing

Temperature dependent magnetoresistance characterization of ordered strainedInGaP grown by MOVPES. Hasenöhrl 1) ,  J. Betko 1) ,  M. Morvic 1) ,  J. Novák 1) ,  J. Fedor 1)1) Institute of Electrical Engineering, Slovak Academy of Sciences, Dubravska cesta 9, 841 04 Bratislava, Slovak Republic1. IntroductionThe MOVPE grown InGaP exhibits tendency to a CuPt−B type of ordering. Physical properties of epitaxial layerswith various degree of order are different. The unequal distribution of the atoms with regard to the crystallographicdirections in ordered layers leads to anisotropic behaviour of material features [1]. In our first report on transportanisotropy in InxGa1− xP [2] we revealed, that the resistivity anisotropy is a feature observable in samples with thehighest degree of order grown at 640 oC. The evaluation of electrical properties using the van der Pauw (vdP)method [3] showed that the layers even slightly mismatched from substrate are electrically anisotropic. The layerexactly lattice−matched to the substrate at the growth temperature showed Hall concentration and Hall mobilitycorresponding with theoretical calculations from [4]. Samples tensile or compressive strained at the growthtemperature exhibited higer Hall mobilities; at 77 K up to 16 000 cm2 V−1s−1. Because these layers exibited alsostructural defects described in [5] we concluded, that the layer inhomogeneity has significant impact on parametersdetermined from measurement in vdP configuration.2. Experimental procedureA set of InxGa1−xP layers was prepared on the GaAs(100) semiinsulating substrates with a 300 nm thick undopedGaAs buffer layer. The low−pressure organometallic chemical vapour phase epitaxy (OMVPE) was operated at atotal pressure of 20 mbar and a growth temperature of 640 oC. Ordering in the layers was confirmed by TEM. Thedegree of the order calculated from 6 K photoluminescence (PL) spectrum peak position for lattice−matched layerwas 0.39. Changing the layer composition xIn  from 0.39 to 0.55 induced the epitaxial strain which influence onelectrical parameters in ordered layers was studied. A set of layers under study is summarized in Table 1.Magnetoresistance measurements were performed on stripe samples using the four−point probe method. 1×8mm2 stripes were prepared by cleaving in two mutually perpendicular crystallographic directions ([011] and[0−11]) and contacted with In alloyed 4 min. at 400 oC in forming gas. The temperature dependentmagnetoresistance measurements were done in LHe continuous flow cryostat with samples in the dark rangingfrom 5K to 300 K. A current of 10 µA was applied to the samples. The magnetic field was varied from −540 to+540 mT. On the stripes also two short−distance contacts were prepared to measure the geometricalmagnetoresistance effect (GMR). GMR measurements were used to calculate so called GMR mobility which isclose to the Hall mobility. Both magnetoresistances, measured with four−point probe (magnetoresistivity) and withtwo short distance contacts (geometrical magnetoresistance), are illustrated in Fig. 1.10th European Workshop on MOVPE, Lecce (Italy) 8−11 June 2003 PS.IV.04S. Hasenöhrl et al 3. Results and discussionSamples with the lattice mismatch lower than ±1×10−3 exhibit a negative magnetoresistance at low magnetic fieldsand at low temperatures. After the simulations we ascribe this feature to the phenomenon of carrier weaklocalization. This is an indication of existence of region with the two−dimensional electron gas (2DEG) probablyat the GaAs−InGaP interface. However, values of Hall mobility estimated from magnetoresistance curvessimulations are much lower than those usually measured in GaAs 2DEG structures with AlGaAs as a barrier. Thelow Hall mobility in the 2DEG and the dependence of resistivity on the crystallographic orientation can be10th European Workshop on MOVPE, Lecce (Italy) 8−11 June 2003 PS.IV.04S. Hasenöhrl et al explained by the strong influence of InGaP barrier/GaAs well interface on carrier transport in the well. There issignificant role of the crystallographic anisotropy of ordered InGaP layer and the interface strain in mismatchedstructures. The resistivity dependence on the crystallographic orientation is higher in samples with higher latticemismatch. Layers with the lattice mismatch higher than ±1×10−3 are electrically anisotropic with strong resistivitydependence on the crystallographic orientation. Samples having [0−11] misfit lines oriented across the stripe probeexhibit considerably higher resistance and magnetoresistance effect than that in samples without misfit. Thisindicates that the [0−11] misfit lines induce high resistance regions across the sample, so the sample becomesinhomogeneous. Therefore, a shortening of the Hall electric field and consequently a large magnetoresistanceeffect occure due to alternating low and high resistive regions across the current flow. As a consequence, themagnetoresistances measured on four contacts stripe probe and between two short−distance contacts are the same,Fig.2. In Tab. 2 the ratio of the van der Pauw resistances R(011)/R(0−11), the resistivity (ro), the Hall mobility(µH), the GMR mobility (µGMR), and the ratio (C) of the "physical" (measured on four contacts probe) and GMR(measured on two short−distance contacts probe) magnetoresistances measured with van der Pauw (vdP) and stripesamples are presented.4. ConclusionIn conclusion, the magnetoresistance measurements on the stripe samples confirmed the anisotropic behaviour oftransport parameters in strained ordered InGaP.References[1] T. Suzuki, MRS Bulletin 22 (1997) 36.[2] Novák, J., Hasenöhrl, S., Kúdela, R., Kucera, M., Wüllner, D., Wehmann, H.−H.: Appl. Phys. Lett. 73 (1998)369.[3] Hasenöhrl S., Novák J., Kúdela R., Betko J., Morvic M., Fedor J.: J. Cryst. Growth 248 (2003) 369.[4] C. Besikci and M. Razeghi, IEEE Trans. on Electron Devices 41 (1994) 1066.[5] S. Hasenöhrl, R. Kúdela, J. Novák, T.O. Tuomi and L. Knuuttila,  Mat. Sci. Eng. B 88 (2002) 134.10th European Workshop on MOVPE, Lecce (Italy) 8−11 June 2003 PS.IV.04S. Hasenöhrl et al 

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Temperature dependent magnetoresistance characterization of ordered strained InGaP grown by MOVPE

ESE - Salento University Publishing

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Temperature dependent magnetoresistance characterization of ordered strained InGaP grown by MOVPE

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