ELECTROPHYSICAL MEASUREMENTS SOLID SOLUTIONS OF InxAl1–xAs

Abstract

Purpose. Layers of InxAl1-xAs, grown at the Novosibirsk Institute of Semiconductor Physics of the Siberian Branch of the Russian Academy of Science that are deliberately unalloyed by means of the MBE method on a semi-insulating substrate InP are widely used in micro-and optoelectronics of the microwave range [1, 2] for broadband wireless communication (satellite, mobile), as well as incomputational logic circuits [3, 4]. The average composition of the solid solution x, according to xray diffraction is 0.490 and 0.5235 (sample C2159 and C2100, respectively), which provides for a good correspondence of the crystal lattice constants in the heterostructure InxAl1–xAs/InP and the possibility of forming a heterojunction with a qualitative interface. The main purpose of this paper is to study the structure of InxAl1–xAs at room temperature. Since InAs and AlAs are semiconductors with crystal structure of sphalerite type [5], the width of the band gap of solid solution InxAl1–xAs is calculated using the model calculation method of interpolation schemes. In [6] it is proved that the empirical Vegard’s law is satisfi ed for the lattice parameter of solid solutions InxAl1–xAs. The best correspondence of the solid solution InxAl1–xAs with the lattice parameter InP (a0 = 5.8690) occurs when the composition value is x ≈ 0.5 [5, 7]. The paper uses the band gap values for binary compounds AlAs and InAs from [5, 7] and the references provided in them. The temperature dependence of the band gap is described by Varshni’s empirical expression. Methods and methodology. Ge/Au/Ni/Au contacts, annealed to the form a ohmic contact, and Ti/Au barrier contacts were applied to the epitaxial layer of the samples. C–V curves of heterostructures InxAl1–xAs/InP were measured at frequencies of the test signal in the range of 103–106 Hz at room temperature. The measurement results demonstrate a pronounced modulation of the charge region with frequencies of the test signal at 104–105 Hz. At lower frequencies a steady leakage currents appear. The paper presents the C–V curves obtained at different frequencies of the test signal. They were further studied in the format of 1/C2(V). It should be noted that the slopes on all the dependences of 1/С2(V) are constant, that is, in the depletion region the graph represents a straight line, which indicates a constant concentration of charge carriers [8]. Results. The effective centre of the energy distribution of the surface state density was estimated using the experimental temperature dependences of the differential conductivity [9, 10]. The maximum curve, whose estimate corresponds to the energy value of 0.49 eV, was observed for the dependences of G(T). As the frequency of the test signal increases, the maximum shifts to higher temperatures. At 106 Hz it completely disappears, presumably due to the application of the through current of differential conductivity. We may thus conclude that the presence of the characteristic maximum of the curve is associated with the parameter of the donor-type centre that causes the phenomenon of current fl ow in the layer with both positive and negative potential on the contact. Conclusion. The electrophysical study shows that a modulation of the spatial charge occurs in the heterostructure InxAl1–xAs/InP, and the processes of current passage are associated with the presence in the band gap of a solid solution InxAl1–xAs of a deep centre with effective energy is 0.49 eV.

Keywords

• solid solutions
• charge localization center
• differential conductivity
• capacity.